CLINICAL MICROBIOLOGY REVIEWS, July 2005, p. 465–483
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Vol. 18, No. 3
Enterotoxigenic Escherichia coli in Developing Countries:
Epidemiology, Microbiology, Clinical Features,
Treatment, and Prevention
Firdausi Qadri,1Ann-Mari Svennerholm,2A. S. G. Faruque,1
and R. Bradley Sack3*
International Centre for Diarrhoeal Disease Research, Bangladesh, and Centre for Health and
Population Research, Mohakhali, Dhaka 1212, Bangladesh1; Department of Medical
Microbiology and Immunology, Go ¨teborg University, 40530 Go ¨teborg, Sweden2; and
Department of International Health, Bloomberg School of Public Health,
Johns Hopkins University, Baltimore, Maryland3
From Discovery to Present Understanding of Public Health Importance......................................................466
LT and ST Enterotoxins........................................................................................................................................466
Colonization Factors ..............................................................................................................................................467
ETEC Strains in Animals......................................................................................................................................469
Age-Related Infections in Children and Adults..................................................................................................469
Relation to Presence of LT, ST, and Colonization Factors..............................................................................470
Single Versus Mixed Infections ............................................................................................................................471
Seasonality of ETEC...............................................................................................................................................471
Comparison of ETEC Diarrhea and Cholera in Children and Adults...........................................................471
Presence of ETEC in Food and Water in the Environment.............................................................................472
ETEC Infections and Malnutrition......................................................................................................................473
Infections in International Travelers...................................................................................................................473
CLINICAL FEATURES .............................................................................................................................................474
Mortality from ETEC Diarrhea............................................................................................................................474
TREATMENT AND MANAGEMENT .....................................................................................................................475
Multidrug Resistance Patterns.............................................................................................................................476
Nutritional and Micronutrient Therapy..............................................................................................................477
Purified CFs and Enterotoxoids ...........................................................................................................................477
Inactivated Whole-Cell Vaccines...........................................................................................................................478
Live Oral ETEC Vaccines......................................................................................................................................478
Acute infectious diarrhea is the second most common cause of
death in children living in developing countries, surpassed only by
acute respiratory diseases accounting for approximately 20% of
all childhood deaths (96). The major etiologic agents that account
for the estimated 1.5 million deaths per year are enterotoxigenic
Escherichia coli (ETEC), rotavirus, Vibrio cholerae, and Shigella
spp. (88, 96); all are known to be endemic in essentially all de-
veloping countries. Whereas V. cholerae, Shigella spp., and rota-
virus can be readily detected by standard assays, ETEC is more
difficult to recognize and therefore is often not appreciated as
being a major cause of either infantile diarrhea or of cholera-like
disease in all age groups. Since ETEC is a major cause of travel-
er’s diarrhea in persons who travel to these areas, the organism is
regularly imported to the developed world (18, 58, 75).
* Corresponding author. Mailing address: Department of Interna-
tional Health, Johns Hopkins Bloomberg School of Public Health, 615
North Wolfe Street, Room W5035, Baltimore, MD 21205. Phone:
(410) 955-2719. Fax: (410) 502-6733. E-mail: email@example.com.
Among the six recognized diarrheagenic categories of Esch-
erichia coli (118), ETEC is the most common, particularly in
the developing world (214). Specific virulence factors such as
enterotoxins and colonization factors differentiate ETEC from
other categories of diarrheagenic E. coli. ETEC belongs to a
heterogeneous family of lactose-fermenting E. coli, belonging
to a wide variety of O antigenic types, which produce entero-
toxins, which may be heat labile and/or heat stable, and colo-
nization factors which allow the organisms to readily colonize
the small intestine and thus cause diarrhea (118, 155, 211).
This review summarizes data on the recognition and impor-
tance of ETEC diarrhea in developing countries, emphasizing
on its prevalence, toxin types, colonization factors, and mor-
bidity in different population groups at risk. We have reviewed
information on ETEC since its discovery almost 50 years ago
(43) and used clinical and laboratory data from hospital and
community-based studies around the world, in both urban and
rural settings, to present a comprehensive picture of ETEC-
mediated diarrheal disease with regard to epidemiology, diag-
nosis, treatment, and prevention through the use of vaccines.
We hope that this review may increase the knowledge and
awareness of the importance of ETEC infections, particularly
in the developing world.
From Discovery to Present Understanding of Public
E. coli was first suspected as being a cause of children’s
diarrhea in the 1940s, when nursery epidemics of severe diar-
rhea were found to be associated with particular serotypes of
E. coli (27). These specific serotypes, designated enteropatho-
genic E. coli, were epidemiologically incriminated as the cause
of the outbreaks. Studies of rabbit ileal loops with these strains
in 1961 (199) showed only a poor correlation of fluid accumu-
lation with the incriminated E. coli serotypes and were not
definitive. Later, however, in volunteer experiments it was con-
firmed that ingestion of large numbers of these organisms
resulted in diarrhea, and the ingested strains were recovered in
the feces (98). Extensive work has been done with this group of
enteropathogenic E. coli and has recently been reviewed (118).
The history of enterotoxigenic E. coli begins in 1956 in Cal-
cutta (43). De and his colleagues injected live strains of E. coli,
isolated from children and adults with a cholera-like illness,
into isolated ileal loops of rabbits and found that large
amounts of fluid accumulated in the loops, similar to that seen
with Vibrio cholerae. However, they did not test the filtrates of
these cultures to determine whether they produced an entero-
toxin. These findings were not followed up until 1968, when
Sack reported studies, also in Calcutta, of adults and children
with a cholera-like illness, who had almost pure growth of E.
coli in both stool and the small intestine (154). These E. coli
isolates were found to produce a strong cholera-like secretory
response in rabbit ileal loops, both as live cultures and as
culture filtrates (74). The patients were also found to have
antitoxin responses to the heat-labile enterotoxin produced by
these organisms (163). At about the same time, similar studies
were being done with animals that also demonstrated strains of
E. coli to be responsible for diarrheal disease in several animal
species: pigs, calves, and rabbits (80, 177, 178). Studies of these
animal enterotoxigenic E. coli paralleled and sometimes pre-
ceded those done with human strains; these organisms were
also found to produce enterotoxins and specific colonization
These findings from Calcutta were soon confirmed by oral
challenge of human volunteers (49, 100) and by corroboration
of studies in Dhaka, Bangladesh (61, 113, 117, 149). ETEC
were shown in these studies to be most frequently found in
children; such findings have been subsequently corroborated in
multiple studies in developing countries (23, 24). Thus, in most
studies in the developing world, ETEC have been shown to be
the most common bacterial enteric pathogen, accounting for
approximately 20% of cases, as shown in Table 1, which sum-
marizes findings from some of the more detailed studies done
in several different countries.
LT and ST Enterotoxins
Following the initial discovery of ETEC in humans, there
was an intensive effort to further characterize its mechanisms
of pathogenesis and means of laboratory identification. Over a
period of several years, its major virulence mechanisms were
identified. ETEC produce one or both of two enterotoxins,
heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST),
that have been fully characterized, cloned, and sequenced, and
their genetic control in transmissible plasmids was identified
(70, 138, 179). ETEC also produces one more of many defined
colonization factors (pili/fimbrial or nonfimbrial), also under
plasmid control (65, 66). The full sequence of laboratory
events leading to the better understanding of virulence factors
TABLE 1. Enterotoxin profiles and presence of colonization factors in enterotoxigenic E. coli strains isolated from symptomatic children in
different regions of the worlda
Parameter BangladeshMexico PeruEgyptArgentinaIndiaNicaragua
Prevalence of ETEC (% of subjects)
Toxin profile (% of subjects)
Prevalence of CF (%)
No. of subjects tested
aData are from Bangladesh (24[a], 132[b]), Mexico (38[c]), Peru (19[d]), Egypt (1[e], 139[f]), Argentina (207[g]), India (180[h]), and Nicaragua (126[i]). NT, not
466 QADRI ET AL.CLIN. MICROBIOL. REV.
in ETEC has been reviewed in a number of publications (66,
157, 116, 118, 158, 211) and will not be elucidated further in
this article. Only a brief summary of the actions of these two
enterotoxins will be given.
LT was found to be very similar physiologically, structurally,
and antigenically to cholera toxin and to have a similar mode
of action. The molecular mass (84 kDa) and the subunit struc-
ture of the two toxins were essentially identical, with an active
(A) subunit surrounded by five identical binding (B) subunits
(70, 83). Following colonization of the small intestine by ETEC
and release of the LT, the LTB subunits bind irreversibly to
GM1 ganglioside, and the A subunit activates adenylate cy-
clase, which results in increases in cyclic AMP, which stimu-
lates chloride secretion in the crypt cells and inhibits neutral
sodium chloride in the villus tips. When these actions exceed
the absorptive capacity of the bowel, purging of watery diar-
rhea results (70).
ST is a nonantigenic low-molecular-weight peptide, consist-
ing of 18 to 19 amino acids. There are two variants, STp and
STh, named from their initial discovery from pigs and humans,
respectively, and which have identical mechanisms of action.
Released in the small intestine, ST binds reversibly to guany-
late cyclase, resulting in increased levels of cyclic GMP (138).
ST has also been implicated in the control of cell proliferation
via elevation of intracellular calcium levels (174). As with LT,
chloride secretion by the crypt cells is then increased and
inhibition of neutral sodium chloride absorption occurs, lead-
ing to outpouring of diarrheal stool. The relative proportions
of LT, ST, and LT/ST toxin-producing ETEC seems to vary
from one geographic area to another in patients with ETEC
diarrhea or asymptomatic carriers (Tables 1, 2, and 3). The
rate of isolation from asymptomatic children has varied be-
tween 0% and 20% in numerous studies carried out with chil-
dren in different settings but has in most instances been lower
than the rates in children with diarrhea (7, 8, 19, 38, 79, 88,
143). On average ETEC is seen at least two to three times
more frequently in symptomatic than asymptomatic children
More than 22 colonization factors (CFs) have been recog-
nized among human ETEC and many more are about to be
characterized (66). The CFs are mainly fimbrial or fibrillar
proteins, although some CFs are not fimbrial in structure (60,
61, 66). Notable among these is CS6, an antigen increasingly
TABLE 2. Examples of case-control studies of symptomatic versus asymptomatic children infected with ETEC of different toxin types
No. of subjects (% positive)
Sao Paulo, Brazil1982AN
All ETEC cases
All ETEC cases
All ETEC cases
All ETEC cases
All ETEC cases
All ETEC isolates
All ETEC isolates
Ethiopia 1982A 184
New Caledonia1993B 13
aThe assays used for detection of enterotoxins on ETEC were adrenal cell and infant mouse (A), DNA probes (B), and GM-1 ELISA (C).
bBased on number of specimens analyzed; the rest are based on number of subjects tested.
VOL. 18, 2005 ETEC IN DEVELOPING COUNTRIES467
being isolated in recent studies. The CFs allows the organisms
to colonize the small bowel, thus allowing expression of either
or both LT and ST in close proximity to the intestinal epithe-
lium. Studies with humans as well as experimental animals
have shown that CF-positive bacteria but not their isogenic
CF-negative mutants colonize and induce diarrhea (60, 66, 100,
A nomenclature for the CFs designating them as coli surface
antigen (CS) was introduced in the mid-1990s (66). A list
showing the old and new classifications of the CFs can be seen
in Table 4. All except CFA/I have the CS designation in the
present designation. Some of the better-characterized CFs can
be subdivided into different families, i.e., the colonization fac-
tor I-like group (including CFA/I, CS1, CS2, CS4, CS14, and
CS17) (66) and the coli surface 5-like group (with CS5, CS7,
CS18, and CS20) (204) and those that are unique (CS3, CS6,
and CS10 to CS12). Within each of these families there are
cross-reactive epitopes that have been considered as candi-
dates for vaccine development (147).
Of the wide range of CFs, the most commonly present on
diarrheagenic strains include CFA/1, CS1, CS2, CS 3, CS4,
CS5, CS6, CS7, CS14, CS17, and CS21 (66). These have been
found on ETEC strains worldwide in various frequencies (Ta-
ble 5). However, CFs have not been detected on all ETEC, and
on roughly 30 to 50% of strains worldwide no known CFs could
be detected. This could be due to the absence of CFs, to loss of
CF properties on subculture of strains, or to lack of specific
tools for their detection.
Besides determination of the toxins and CFs, serotyping, i.e.,
determination of O serogroups associated with the cell wall
lipopolysaccharides and H serogroups of the flagella, has been
used to identify and characterize ETEC (124). In early studies
in, e.g., Bangladesh, it was suggested that typing of the most
prevalent serotypes might be used to identify ETEC (112).
However, as shown in numerous studies in different countries,
clinical ETEC isolates may belong to a large number of sero-
types. Furthermore, ETEC serotype profiles may change over
Based on an extensive database analysis of ETEC from a
number of different countries all over the world, Wolf reported
that in the ETEC antigen the largest variety was the O antigen
(211). Thus, 78 different O groups were detected in the 954
ETEC isolates included in the study (hereafter called the
ETEC database). In addition, there were several rough strains
that lacked side chains, thus being nontypeable with regard to
O antigen, or strains that had unknown serogroups. The most
common O groups in this retrospective study were O6, O78,
O8, O128, and O153; these accounted for over half of the
In a more recent study in Egypt, a large variation of O
groups was also recorded, with 47 O groups being represented
among the 100 ETEC strains isolated; however, an entirely
different O group pattern was recorded than in the database,
the most common O groups in the Egyptian study being O159
and O43 (128).
Considerably fewer H serogroups than O serogroups are
associated with ETEC. Thus, a total of 34 H groups were
identified among the 730 ETEC strains included in the ETEC
database (211). Five H types accounted for over half of those
strains and they were widespread. Similarly, five different H
types accounted for almost half of 100 ETEC strains isolated
prospectively from Egyptian children, although different H
types predominated from those reported for the ETEC data-
TABLE 3. Toxin profile of ETEC strains isolated from children
with diarrhea selected during different years in various
% of strains
aETEC from children with diarrhea or asymptomatic carriers.
TABLE 4. Past and present designations for colonization factors
aAbbreviations: F, fimbrial; f, fibrillae; nF, nonfimbrial; H, helical. All except
CFA/I have the CS designation (66).
468QADRI ET AL.CLIN. MICROBIOL. REV.
There are clearly preferred combinations of serotypes, CFs,
and toxin profiles in ETEC. For instance, certain H groups are
strongly associated with an O serogroup, such as O8:H9, O78:
H12, and O25:H42, and some O and H serogroups are asso-
ciated with one or more CFs (112, 214). In a study of ETEC
isolated from children in Argentina, it was shown that most
CFs were expressed by strains exhibiting a limited array of
serotypes, while the ETEC strains that lacked detectable CFs
belonged to many different serotypes (207). However, the sig-
nificance of these different combinations regarding enhanced
virulence (211) or for vaccine development is still unclear.
Serotyping appears to give an indication of the variety of
strains that are present in a particular ETEC type in a certain
geographical area. A close genetic relationship has been found
within ETEC strains belonging to a certain serotype, which is
different from that noted in other serotypes, and the pattern of
genetic relatedness did not change over a period of 15 years
(125). The loss of CFs and toxin phenotypes did not affect the
genetic relatedness of these strains and their clonal relation-
ship, which suggests that serotype analysis can be coupled to
genetic typing for studying the clustering of strains for epide-
miological and pathogenetic studies of ETEC. Altogether, the
great variation in O and H serogroups in ETEC makes sero-
typing less suitable for identification of these bacteria and
makes O and H antigens less attractive as putative candidate
antigens in an ETEC vaccine.
ETEC Strains in Animals
ETEC is also a major cause of severe diarrheal disease in
suckling and weanling animals (66, 115). Animal ETEC strains
are known to produce enterotoxins similar to those of human
strains and to possess species-specific CFs. The LT from ani-
mal strains, designated LT1, is similar to the LT produced by
human ETEC; however, another variety designated LTII is
only found in animals and is not associated with clinical dis-
ease. Animal strains produce two major types of ST, desig-
nated STa (STI) and STb (STII). STa, which is a small mole-
cule of ca. 2.0 kDa, was the first of the enterotoxins to be
identified in animals (177). As in humans, both STh (STIb) and
STp (STIa) may be produced by animal strains. Animal strains
(rarely human strains) can also produce STb, a slightly larger
ST (ca. 5 kDa), which does not activate intracellular nucleotide
levels and whose mechanism of action is poorly understood
Like human ETEC, animal strains also have distinct binding
proteins (adhesins and fimbriae), which allow the organisms to
attach and colonize the small intestinal mucosa. Indeed, ETEC
CFs display a remarkable species specificity, and colonization
factors are clearly different from those of human and animal
ETEC. Their genetic control may be in plasmids or in the
chromosome. The most common of these have been desig-
nated K88, K99, and 987P, but there are at least another eight
or more, which have other designations. The animal coloniza-
tion factors are now being identified by F numbers, such as F4,
F5, and F6 instead of K88, K99, and 987P (65). Because of the
specificity of these adhesins, animal ETEC strains normally do
not infect humans. This is in contrast to other diarrheagenic E.
coli, such as those that produce Shiga-like toxins, e.g., O157:
H7, which are found in animals, mainly cows, and produce
severe disease in humans (92)
Age-Related Infections in Children and Adults
Studies over the last few years have documented that ETEC
is usually a frequent cause of diarrhea in infants younger than
2 years of age (132, 139, 183). In Egypt it was found to be the
most common cause of diarrhea in the study infants, account-
ing for about 70% of the first episodes (139). The incidence
was higher in males than females. In a detailed investigation in
children 0 to 5 years in Bangladesh, 90% of cases of ETEC
diarrhea reporting to the hospital were children aged from 3
months to 2 years (132). In an ongoing birth cohort study in
Bangladesh, it was found to be the most common cause of
diarrhea in children 0 to 2 years of age, accounting for 18% of
The susceptibility of infants and young children has also
been observed in other settings which have poor public health
and hygiene conditions. The characteristics of the toxin types
and CFs present on ETEC strains isolated from young children
vary among countries where ETEC is endemic (139, 183, 215).
A comparison is shown for Bangladesh and other developing
TABLE 5. Colonization factor profiles of ETEC isolated from children with diarrhea in different countries
% of strains expressing indicated CF
CS7 CS17CS14 Other
CS1?3 CS2?3 CS3CS4?6 CS5?6 CS6
aIndicates % of ETEC with any CF.
bETEC from children with diarrhea or asymptomatic carriers.
VOL. 18, 2005ETEC IN DEVELOPING COUNTRIES469
countries (Tables 1 to 5). Studies to better understand the
natural infection pattern of ETEC are being conducted with
cohorts of infants to discern the infection and reinfection pat-
tern as well as the age group most at risk for infection. In
studies of infants in West Africa, Egypt, and Bangladesh, the
rate of ETEC infections in community-based studies increased
from about 3 to 6 months of age, similar to the surveillance
data of hospitalized patients in a diarrheal hospital in Bang-
ladesh (139, 183, 215). The age at which a primary ETEC
infection can be documented depends to some extent on the
phenotype of ETEC that is infecting the child. In a study in
Guinea Bissau, it was reported that in the youngest age group,
3 months, ETEC strains producing STh and LT were most
common, whereas at 6 to 7 months ETEC strains producing
STp, STpLT, and SThLT predominated (183).
The incidence of ETEC infections in developing countries
decreases after 5 years of age with a decrease of infections
between the ages of 5 to 15 years (Table 6). The incidence
increases again in those over 15 years of age and about 25% of
ETEC illness is seen in adults (113, 132). Limited epidemio-
logical information is available for adults, and those available
are mostly from India and Bangladesh. It was in these settings
that ETEC was first described extensively and was shown to be
a cause of adult diarrhea resembling cholera in the severity of
infection (113, 149, 154). It thus became obvious that adults
with severe dehydrating cholera-like illness attributable to
ETEC infections are not uncommon (132, 214). In hospitalized
patients, adults often present with more severe forms of ETEC
diarrhea than children and infants (Table 7). Interestingly,
further analyses have shown that the elderly are also suscepti-
ble to ETEC infections requiring hospitalization (62). ETEC
was found to be the second most frequently isolated (13%)
bacterial pathogen after V. cholerae O1 (20%). In this age
group (?65 years), patients also presented with more severe
dehydration than children.
The reason why ETEC infections decrease after infancy and
increase at adulthood may be due to both environmental and
immunological factors. Data obtained from studies in animals
indicated changes with age in the presence of intestinal cell
receptors for K99 fimbrial antigen produced by ETEC infect-
ing animals (148). Another factor could be the immunogenet-
ics and diversity between individuals, which may prevent or
predispose to ETEC infections (33, 69) or increased immune
responses due to repeated infections in early childhood, which
may decrease due to fewer infections during adolescence (Ta-
Relation to Presence of LT, ST, and Colonization Factors
Indeed, ETEC expressing LT only have been considered less
important as pathogens, especially since they are more fre-
quently isolated (than the other two toxin types) from healthy
persons than from patients (33). This could be related to the
low prevalence of CFs on the LT-producing ETEC strains (66,
110). Thus, in many epidemiological studies, the CFs have
been detected on less than 10% of LT-producing ETEC
strains, compared to over 60% of the ST- and LT/ST-express-
ing ETEC. However, it cannot be excluded that LT-producing
ETEC strains may be highly pathogenic, given that they may
have been isolated from sick patients with severe dehydrating
diarrhea (Table 8).
A comparison of the toxin pattern of the infecting strains in
TABLE 6. Toxin profiles of ETEC isolated from patients of
different age groups in a hospital in Bangladesha
No. (%) of subjects aged:
0–23 mo 24–59 mo5–14 yr
aData are from the surveillance for ETEC from 1996 to 2000 from patients
with diarrhea enrolled in the 2% systemic routine surveillance system at the
ICDDR in Bangladesh (185). The numbers of patients and percent positive for
the respective toxins are shown. Data are from patients infected with ETEC as
a single pathogen.
TABLE 7. Clinical characteristics of adults and children hospitalized with ETEC, V. cholerae O1, and rotavirus diarrhea in Dhaka,
Bangladesh, from 1996 to 2002a
% of adults % of children
(N ? 478)
V. cholerae O1
(N ? 1,417)
(N ? 1107)
V. cholerae O1
(N ? 865)
(N ? 3,406)
Stool with blood
aData are from 15,558 patients seen at the diarrhea hospital in Bangladesh based on the routine surveillance for enteric pathogens (185). The age of the children
ranged from 0.1 to 36 months (median, 0.83 years) and that of the adults from 15 to 80 years (median, 30 years), *, P ? 0.001 in comparisons (*) between adults with
ETEC or V. cholerae O1 diarrhea; (†) between children with ETEC or rotavirus diarrhea in comparison to V. cholerae O1 diarrhea; (‡) between adults and children
with ETEC diarrhea. For rotavirus diarrhea only, data from children are given.
470 QADRI ET AL.CLIN. MICROBIOL. REV.
patients hospitalized with diarrhea in the different age groups
shows that the toxin phenotype did not change with age (132)
(Table 6). In longitudinal studies with infants, both LT and ST
phenotypes of ETEC were found to be associated with diar-
rhea (1, 37). This has been shown to be the case also in
hospital- (7, 8) as well as community-based studies (1, 37).
However, in hospital-based studies (132), ETEC producing
both LT and ST or ST alone were found to cause relatively
more severe disease than that caused by LT-producing ETEC
strains (Table 8).
Although over 22 CFs have been detected on ETEC (Table
4), only six to eight are more frequently isolated from diarrheal
stools (Table 5). Of these, CFA/I and CS1 to CS6 are the
predominant types (66). These CFs are mostly present on
ETEC producing ST or both LT and ST. It is believed that
immunity to strains that express the nonimmunogenic ST is
derived from the anti-CF response to the protein adhesins.
Thus, in the development of vaccines, these CFs as well as LT
are being included to give a broad-spectrum protection (189,
The relationship between the presence of colonization fac-
tors and the disease-producing capability in ETEC diarrhea
has been analyzed in many different epidemiological settings.
In community-based studies the risk of diarrhea increased
when a CF was present on the infecting strain (1). In Bang-
ladesh the presence or absence of CFs on ETEC could not be
associated with the severity of diarrhea in hospitalized patients
(Table 8) (132). Studies in Mexico suggest that there is a
reduced risk of diarrhea in infants if there was reinfection with
ETEC producing the same compared with different CFs (38).
In volunteer challenge studies, protection was observed to
ETEC with the same CF as that present on the vaccine strain
(97). Some CFs are seen more often in infants than in adults,
suggesting that natural immunity to infection may develop.
Thus, studies in Bangladesh have shown that almost all ETEC
expressing CS7 and CS17 were isolated from children less than
3 years of age (132). LT-producing ETEC strains expressing
CS7 were also most pathogenic in a birth cohort in West Africa
whereas CF-negative strains were not, suggesting that the pres-
ence of a CF, even in the absence of ST, enhances the virulence
of ETEC (183).
Single Versus Mixed Infections
Coinfection with ETEC and other enteric pathogens is com-
mon, which may lead to problems in determining whether the
symptoms are caused by the actual ETEC infection and un-
derstanding the actual pathogenesis of the infection (134, 182).
Mixed infections are frequent and may be seen in up to 40% of
cases (7, 17, 127, 132, 139). The presence of enteric pathogens
in asymptomatic persons is also known to be high in areas of
poor sanitation. The incidence of mixed infections seems to
increase with age in studies in Bangladesh and fewer copatho-
gens were seen in infants than in older children and adults with
ETEC diarrhea (134). In cases of mixed infections in children,
rotavirus is the most common, followed by other bacterial
enteropathogens, e.g., V. cholerae, Campylobacter jejuni, Shi-
gella spp., Salmonella spp., and Cryptosporidium (7, 67, 166). In
traveler’s diarrhea, enteroaggregative E. coli and Campy-
lobacter spp. have been common pathogens together with
ETEC (2, 127).
Seasonality of ETEC
Several studies have reported that ETEC diarrhea and
asymptomatic infections are most frequent during warm peri-
ods of the year (1, 8, 79, 103, 132, 139, 167, 183), suggesting
that travelers to these regions are also more at risk to develop
ETEC infections during the warm seasons. In Bangladesh,
ETEC follows a very characteristic biannual seasonality with
two separate peaks, one at the beginning of the hot season, that
is, the spring, and another peak in the autumn months, just
after the monsoons, but it remains endemic all year (8, 94, 132,
146) (Fig. 1). Such a seasonality may be initiated by climate
and spread by environmental factors. As the atmospheric tem-
perature increases when spring sets in after the cooler winter
months, there is increased growth of bacteria in the environ-
ment and this continues in the summer months. Furthermore,
with the advent of rains in the monsoon season, there is en-
hanced contamination of surface water with fecal material and
the surface water can thus become heavily contaminated (146).
A seasonality for the different toxin phenotypes has also been
suggested, with ST-producing ETEC strains being more com-
mon in the summer (1, 139) whereas LT-producing ETEC
strains are present all year round and do not show any season-
ality (Fig. 2).
Comparison of ETEC Diarrhea and Cholera in Children
In Bangladesh cholera and ETEC diarrhea are still endemic
(134, 165). Both diseases share a biannual periodicity, peaking
once in the spring and again in the autumn (Fig. 1) and re-
maining endemic all year (63). In the spring ETEC infections
appear to be more prevalent than V. cholerae O1 infections
(Fig. 1). In a recent 4-year study, carried out for the surveil-
lance for cholera in rural Bangladesh (165), it was found that
ETEC and not V. cholerae was often the cause of the diarrhea
in some of these field areas (215). It is also not surprising to
have concomitant outbreaks of both ETEC and V. cholerae
during peak seasons and during outbreaks (31, 63). Active
screening for ETEC needs to be carried out in outbreaks and
TABLE 8. Association of severity of disease with toxin type and
presence of known colonization factors on ETEC in children up to 3
years of age in rural Bangladesh during a 2-year surveillancea
CF and toxin
No. (%) with symptoms that were:
aCF types were studied with a panel of 13 different monoclonal antibodies
against the most prevalent CFs (66, 132). The degree of dehydration of the child
from whom the ETEC strain was isolated is indicated. The strains were isolated
from children in the hospital at Matlab in Bangladesh. Data are from patients
infected with ETEC as a single pathogen. A significant difference (P ? 0.05) was
only seen between ETEC strains positive for ST (P ? 0.001) or LT/ST (P ?
0.001) and LT. The latter were isolated at significantly lower frequencies from
children with moderate dehydration. Chi square for trends was used for statis-
VOL. 18, 2005ETEC IN DEVELOPING COUNTRIES 471
epidemics for both epidemiological and public health pur-
A large proportion of patients with ETEC infection have
short stays in the hospital and only about 5% of patients need
to be hospitalized for longer periods of time. The length of stay
at the hospital is similar for patients infected with any of the
three toxin phenotypes of ETEC. Few patients go on to
chronic illness (?14 days). Patients with ETEC diarrhea and
cholera have similar clinical characteristics and differ mainly in
the rates of severe dehydration (Table 7).
Presence of ETEC in Food and Water in the Environment
Diarrhea due to ETEC, like other diarrheal illnesses, may be
the result of ingestion of contaminated food and water (26, 40,
87, 99, 121, 122). In any situation where drinking water and
sanitation are inadequate, ETEC is usually a major cause of
diarrheal disease. Surface waters in developing countries have
been found to harbor these organisms (14, 121) and transmis-
sion can occur while bathing and/or using water for food prep-
aration. These forms of transmission are common in area
where it is endemic both in the local populations and in inter-
national travelers to these areas (see the later section on trav-
Transmission of ETEC by processed food products outside
of the developing world is less commonly seen but well docu-
mented. In 1977, Sack et al. found that of 240 isolates of E. coli
from food of animal origin in the United States, 8% were
found to contain ETEC which produced either or both LT and
ST (164). None of these food products were associated with
diarrheal outbreaks. In studies carried out in the 1970s in
Sweden, however, outbreaks of diarrhea due to food-borne
ETEC were reported (41). Similar findings were reported from
Brazil in 1980 (144); 1.5% of 1,200 E. coli strains from pro-
cessed hamburger or sausage were found to be ETEC. ETEC
transmission on cruise ships has now been reported on several
occasions (40). These findings suggested that since ETEC is
not uncommonly found in meat and cheese products, these
organisms have the potential for producing diarrheal out-
breaks in different parts of the world.
Contaminated weaning food is also a likely cause of ETEC
diarrhea in infants (139, 146). Contaminated food and water
sources both contribute to seasonal outbreaks which affect
tourists. Thus, ETEC is a cause of traveler’s diarrhea more
often in the warm than in the cool season. In a study in Bolivia
it has been shown that ETEC could be isolated from a sewage-
contaminated river (121). Furthermore, contaminated food
and water were found to be the source of ETEC infections in
Surface water sources in Bangladesh, in both rural and ur-
ban areas, are highly contaminated with ETEC. Thus, recently
in a study in Bangladesh, ETEC strains were obtained from
clinical samples as well from ponds, rivers, and lakes around
the clinical field site. In this study it was found that 32% of
water samples obtained from the surface water sources were
contaminated with ETEC and that the toxin and CF pheno-
FIG. 1. Estimated numbers of enterotoxigenic E. coli and V. cholerae O1 isolated from diarrheal stools of children under 5 years of age from
surveillance carried out from 1996 to 2002 at the International Centre for Diarrheal Disease Research hospital in Dhaka, Bangladesh. The figure
indicates monthly isolation of ETEC (Œ) and Vibrio cholerae O1 (■).
FIG. 2. Monthly incidence of ETEC diarrhea in Abu Homas, Egypt,
showing that ST-producing ETEC was more common in warmer months,
while LT-producing ETEC was present at similar levels throughout the
year. Reproduced from reference 139 with permission.
472 QADRI ET AL.CLIN. MICROBIOL. REV.
types of strains isolated from the clinical and environmental
samples were comparable (14). Furthermore, pulsed-field gel
electrophoretic analysis of the ETEC strains showed that those
present in the environment were similar to the clinical isolates,
supporting that, as seen for V. cholerae, surface waters may be
a major source for the survival and spread of ETEC.
Studies in communities where personal hygiene, education,
and general living conditions are poor have shown that infec-
tion can spread within family groups. In one study on ETEC
infections in Bangladesh, the bacteria were spread to 11% of
contacts in a 10-day study period (25); transmission was de-
pendent on socioeconomic status and living conditions. Con-
taminated food and water and the mothers themselves, who
are food handlers, seem to be the reservoirs for such infections
(54). It is not surprising therefore that the possession of a
sanitary latrine significantly decreased the risk of ETEC diar-
rhea in children in Egypt (1). On the White Mountain Apache
reservation in Whiteriver, Arizona, where ETEC was found to
be an important cause of diarrhea in children, these organisms
were also found in river water, sites of large gatherings of
Apaches on festive occasions (162). Although ETEC has been
detected as a cause of diarrhea in Apache children in Arizona
(162), where water and sanitation were suboptimal, subsequent
studies in the developed world where water supplies and san-
itation are optimal show very low frequencies of ETEC in
children with diarrhea (156).
ETEC Infections and Malnutrition
As for other diarrheal diseases, preexisting malnutrition can
lead to more severe enteric infections, including those caused
by ETEC, possibly due to the immunocompromised nature of
the host that also predisposes these individuals to a greater
bacterial load on the mucosal surfaces of the gut than the
well-nourished child (28).
In a study in India, diarrheal illness including that caused by
ETEC was found to be more severe in children with malnutri-
tion (107). Micronutrient deficiency such as vitamin A and zinc
is quite common in developing countries and generally in-
creases the morbidity due to diarrheal illnesses (137, 140),
although the effect on the morbidity of ETEC diarrhea has not
yet specifically been studied. It has been estimated that in
Bangladesh over 40% of children younger than 5 years of age
may have zinc deficiency (131, 168). Supplementation with zinc
increases the adaptive immune responses to cholera vaccina-
tion in children and adults (9, 91, 131) and in children with
shigellosis (140). The effect of micronutrient deficiency on the
morbidity and protective immune responses in ETEC diarrhea
has not been specifically studied but is an area that needs
attention. However, repeated diarrheal episodes including
those induced by ETEC may be an important cause in predis-
posing the child to malnutrition (22, 106).
Other factors, such as breast feeding, may have the capacity
to prevent ETEC diarrhea. Factors in milk such as specific
secretory immunoglobulin A antibodies and receptor ana-
logues (85) as well as innate and anti-inflammatory factors may
all contribute to decrease the infection. Hyperimmune bovine
colostrum containing high titers of ETEC CF antibodies has
been shown to provide temporary protection against ETEC
challenge (64) but is not suitable for public health application
(198). Breast feeding reduces overall diarrhea and mortality
(71, 205). A reduction in diarrheal episodes has been seen in
infants who had been breastfed for the first 3 days of life,
irrespective of other dietary practices, emphasizing the positive
effects of colostrum (34). Studies in Bangladesh have shown
that breast milk antibodies against cholera toxin and lipopoly-
saccharide do not protect children from colonization with V.
cholerae but do protect against disease in those that are colo-
Protection from cholera in breastfed infants of mothers im-
munized with killed cholera vaccine could not be correlated to
antibacterial and antitoxic antibodies in breast milk, suggesting
that the reduced transmission of pathogens from the mother to
the infant had a protective effect (35). Since secretory immu-
noglobulin A antibodies to CFs and enterotoxin are present in
breast milk samples from mothers in developing countries (39,
84, 187), it would be natural to assume that breastfed infants
should be protected from ETEC diarrhea. However, epidemi-
ological studies show that partial breast feeding does not result
in a reduced risk of ETEC diarrhea. However, in data obtained
in various studies, it appears that exclusive breast feeding prac-
tices have a positive effect of decreasing the severity and/or
incidence of ETEC infections (34, 102, 136). This effect is short
term and does not last long after infancy, and an overall pro-
tection is not seen in the crucial first 2 to 3 years of life (1, 34,
The limited capacity of breast milk to protect against ETEC
diarrhea in developing countries can also be attributed to other
social and behavioral factors. These include the introduction of
contaminated water and weaning food in the child’s diet, lead-
ing to increased symptomatic as well as asymptomatic ETEC
infections. In Mexico, the incidence of diarrhea increased even
in the first 3 months of age if a barley drink was given to the
infant (102). Since mixed feeding is started quite early in life in
a majority of infants in developing countries, sometimes as
soon as after birth, contaminated water may also be the cause
of a multitude of infections (146). The importance of personal
hygiene rather than breastfeeding appeared to be more pro-
tective against ETEC diarrhea in Egypt (1).
Infections in International Travelers
ETEC remains endemic all year round but is highest during
the warm season, reflecting the seasonal difference of ETEC
and other bacterial enteropathogens in the country visited
(109, 175), suggesting that travelers are more vulnerable to the
diarrheal illnesses at these times. In travelers, the phenotypes
of ETEC strains vary from country to country, e.g., LT-only
ETEC was more commonly isolated from visitors to Jamaica,
58% (90), and LT/ST ETEC was most often seen in visitors to
India, 45% (90), and ST-only ETEC in visitors to Kenya, 51%
(175). Thus, strains that are circulating in a particular country,
infecting primarily children, and contaminating the water and
food sources (as well as the hands of the food handlers) may
determine the type of ETEC infecting the travelers. Travelers
to such countries do not know the cause of their diarrheal
illness since it cannot be identified on site, outside of research
studies. The data available suggest that from 20 to 40% of
traveler’s diarrhea cases (18, 90, 159, 175) may be caused by
ETEC, and the children resident in those countries have rates
VOL. 18, 2005ETEC IN DEVELOPING COUNTRIES 473
of 20% of hospitalized diarrheal episodes caused by ETEC.
Thus, ETEC seems to be the most frequent cause of traveler’s
diarrhea in North Americans and Europeans visiting develop-
ing countries (58, 145, 150, 175, 213).
The diarrheal disease caused by ETEC that was first recog-
nized consisted of a cholera-like illness in both adults and
children in Calcutta (161). Since then, many studies around the
world have shown that ETEC-induced diarrhea may range
from very mild to very severe. There are, however, short-term,
asymptomatic carriers of the organisms (20).
The diarrhea produced by ETEC is of the secretory type: the
disease begins with a sudden onset of watery stool (without
blood or inflammatory cells) and often vomiting, which lead to
dehydration from the loss of fluids and electrolytes (sodium,
potassium, chloride, and bicarbonate) in the stool (25, 157).
The loss of fluids progressively results in a dry mouth, rapid
pulse, lethargy, decreased skin turgor, decreased blood pres-
sure, muscle cramps, and eventually shock in the most severe
forms. The degree of dehydration is categorized from mild to
severe, and this clinical distinction is important in the provision
of adequate therapy. The patients are afebrile. Usually the
diarrhea lasts only 3 to 4 days and is self-limited; if hydration
is maintained, the patients survive, and without any sequelae.
With adequate treatment, the mortality should be very low
The pathophysiology of the illness caused by ETEC is es-
sentially the same as that caused by Vibrio cholerae (94) and the
clinical picture is identical, especially in adults (Table 7). Stud-
ies with human volunteers have shown that the infecting dose
is high for both diseases. For ETEC, the dose is around 106to
1010CFU, with lower doses being less pathogenic (100). The
need for a large infectious dose, the proliferation of the bac-
teria in the small bowel through colonization factors and the
production of enterotoxins, and the watery, secretory type of
diarrhea which produces clinical dehydration are comparable
in both diseases. Both organisms produce an immunologic
protective response, reflecting the observation that the attack
rates are higher in children and decrease with age (24, 134).
In Bangladesh, the majority of cases of acute watery diar-
rhea, especially in children, are caused by three pathogens,
rotavirus, V. cholerae, and ETEC (7, 8, 24). Hospital-based
studies during the early 1980s have demonstrated that the
purging rate is higher in cholera compared to the other two
illnesses (114). A comparison of the clinical features of the
disease in adults with ETEC and V. cholerae infections seeking
care at the hospital in Bangladesh shows that ETEC disease
differs significantly from V. cholerae infections in the severity of
dehydration (Table 7), although both infections can result in
severe dehydration. In comparison to children, adults with
ETEC diarrhea seem to have more dehydrating illness, requir-
ing longer hospitalization and more intravenous fluid manage-
ment. This may be because of more delay in reaching a treat-
ment facility. In children, rotavirus and ETEC diarrhea share
similar clinical characteristics but differ from cholera in being
less severe (Table 7).
It should be mentioned that the adult form of ETEC-related
disease (of considerable severity) seems to be identified more
in the Indian subcontinent. There are few (if any) reports of
ETEC in adults, other than in traveler’s diarrhea. This may be
due to the lack of diagnosis in adults, again because of the lack
of easily available laboratory techniques.
Mortality from ETEC Diarrhea
Mortality data due to ETEC infections are difficult to esti-
mate. Similar to cholera, if patients with severe ETEC disease
reach an adequate treatment center, mortality should be very
low, ?1%. Although untreated cholera patients may have a
high mortality (?50%), untreated ETEC patients would be
expected to have a lower mortality rate based on the lesser
severity of illness overall. In a World Health Organization
report it has been suggested that there are 380,000 deaths
annually in children less than 5 years of age that are caused by
ETEC (214). However, there are no well-documented mortal-
ity figures for ETEC-induced diarrhea, because the microbio-
logic diagnosis cannot be done easily in many settings, and
therefore only rates for cholera, which is cultured easily, can be
accurately determined. ETEC-related deaths at present would
be counted as diarrheal deaths in many countries. It is pre-
sumed, however, that there is significant mortality in patients
not receiving treatment.
Since ETEC must be recognized by the enterotoxins it pro-
duces, diagnosis must depend upon identifying either LT
and/or ST. Because the assays necessary were very cumber-
some, it was thought that some other marker could be a proxy
in identification. Initially the serogroups of ETEC were iden-
tified and found to be relatively few, and therefore it was
thought that perhaps serotyping could be used to differentiate
ETEC from other E. coli, including the enteropathogenic
strains whose characteristic serotypes were known (124). Se-
rotyping was found to be of limited use in Bangladesh (113,
152, 186) and when it became clear that a very large number of
E. coli serotypes could be enterotoxigenic, this was abandoned.
Direct identification of the enterotoxins of ETEC has
evolved over the past 35 years. Physiologic assays, the rabbit
ileal loop model for LT (43), and the infant mouse assay (44)
for ST were initially used as the gold standards before other
simpler assays could be identified. Because LT was strongly
immunogenic whereas ST was not, diagnostic assays developed
along different lines. In 1974 the direct action of LT on two
tissue culture cell lines, Y1 adrenal cells (46) and Chinese
hamster ovarian cells (78), was found to be provide physiolog-
ical responses that could be detected by morphological changes
in tissue culture. These changes were specific for LT and could
be neutralized by antitoxin. The two tissue culture assays were
widely used for LT recognition until the development of the
enzyme-linked immunosorbent assay technology in 1977 (217).
Other assays such as staphylococcal coagglutination (32), pas-
sive latex agglutination (173), immunoprecipitation in agar,
and the Biken test (86) were found to be specific but were not
474QADRI ET AL.CLIN. MICROBIOL. REV.
used widely for diagnostic purposes. Enzyme-linked immu-
nosorbent assays became a widely used method for detecting
LT, particularly using microtiter GM1 ganglioside methods
(190, 196). Subsequently, combined GM1 enzyme-linked im-
munosorbent assays for ST and LT were developed (196, 197)
and have been used in different epidemiological studies (1, 16,
126, 128, 132).
ST testing in infant mice continued to be used widely and
could be enhanced by the use of culture pools, thereby mini-
mizing the numbers of infant mice. In 1981 Gianella developed
a radioimmunoassay for ST which compared favorably with the
infant mouse assay (68).
In 1980, methods using molecular diagnostic techniques be-
gan. Moseley et al. (104) showed that the genes controlling the
enterotoxins could be detected using32P-labeled DNA probes
derived from plasmids for both LT and ST. This method was
shown to be specific and sensitive and could detect as few as 1
to 100 CFU per gram of material (53, 82). Variations of this
technology, including both polynucleotide and oligonucleotide
probes with both radioactive and nonradioactive labeling, have
been found to be useful in detecting ETEC both in clinical and
environmental samples and is widely used (7, 53, 82).
In 1993, PCR was first used in ETEC diagnosis (123). It was
found to be useful for diagnosis directly on fecal material as
well as of isolated colonies (172). It was also adapted to a
multiplex form so that the diagnosis of LT- and ST-producing
organisms as well as other diarrheagenic E. coli can be made
simultaneously (181, 200, 208, 209).
During recent years DNA probes, with either radioactive or
nonradioactive detections or GM1 enzyme-linked immunosor-
bent assays using monoclonal antibodies against ST or LT have
been the most widely used methods for detection of ETEC
toxins (7, 133, 183, 188).
For detection of ETEC colonization factors a number of
different methods have been used during the years. Initially the
capacity of E. coli CFs to agglutinate certain species of eryth-
rocytes in a mannose-resistant manner was used for demon-
stration of CFA/I and CS1, CS2, and CS3 (60). This nonprecise
method was soon replaced by more specific slide agglutination
and immunodiffusion tests initially using polyclonal sera and
subsequently monoclonal antibodies against different CFs (5,
76, 110). Other methods that were used included nonspecific
salting-out tests (16) and binding to tissue culture cell lines
(42). These assays have now been replaced by different molec-
ular methods, e.g., DNA probes and PCR methods against
most of the known CFs or dot blot assays using several differ-
ent anti-CF monoclonal antibodies (133, 139, 180, 182).
The method of choice varies from one laboratory to another
and is dependent on the capability of the investigator and the
level of development of the laboratory where the work is being
carried out. The phenotypic methods can be set up relatively
easily in different laboratories and are useful for prospective
studies; most reagents are not available commercially but may
be obtained from different laboratories. One point to bear in
mind is that the virulence antigens are encoded by plasmid
genes and can be easily lost or become silenced due to the loss
of regulatory genes (182). The more recently developed DNA
probe methods have the capacity to detect the structural genes
for toxins and CFs and thus have the advantage of detecting
ETEC from samples which have been stored for long periods
of time and where phenotypic changes may have taken place.
These procedures are more difficult to adapt to field sites in
developing countries, where laboratory facilities may be inad-
equate for molecular microbiological methods. Furthermore,
in some instances ETEC CFs can only be detected by molec-
ular but not phenotypic methods, since they are not exposed on
the bacterial surfaces due to mutation of genes required for
surface expression (119).
Unfortunately, in spite of all these available techniques,
there are still no simple, readily available methods that can be
used to identify these organisms in minimally equipped labo-
ratories. For that reason many laboratories conducting studies
on diarrhea in developing countries do not include ETEC in
their routine diagnostic capabilities, and special research or
referral laboratories are necessary to identify these bacteria.
TREATMENT AND MANAGEMENT
The treatment of diarrheal disease due to ETEC is the same
as that for cholera or any other acute secretory diarrheal dis-
ease. The correction and maintenance of hydration is always
most important. Antimicrobials are useful only when the diag-
nosis or suspicion of ETEC-related diarrhea or cholera is
made. Provision of adequate nutrition is critical in children in
the developing world, where all diarrheal diseases are fre-
quent. The guidelines for therapy of all diarrheas have been
widely disseminated by the World Health Organization (216).
Rapid rehydration using intravenous fluids (such as Ringer’s
lactate) is required initially for all patients with severe dehy-
dration. After restoration of blood pressure and major signs of
dehydration, patients can be put on oral rehydration solutions
for the remainder of therapy. For all other patients with lesser
degrees of dehydration, therapy with oral rehydration solutions
alone can be used until the diarrhea ceases. Details of man-
agement of acute gastroenteritis in children have recently been
summarized by King and colleagues (6, 95).
The use of antimicrobials in the treatment of ETEC diar-
rhea is problematic, since an etiologic diagnosis cannot be
made rapidly. This differs from the treatment of cholera, an
epidemic disease, where clinical findings and rapid laboratory
tests can readily lead to correct diagnosis. In cholera treat-
ment, antimicrobials are an integral part of therapy because
they lead to a marked decrease in stool output and shortening
of the disease (30, 95). Because childhood diarrheas, however,
are caused not only by ETEC but also by other bacterial and
viral agents, and the clinical presentations are not sufficient to
differentiate them, it has been difficult to study the effect of
antimicrobials in children with ETEC disease and antimicro-
bials are not used routinely in treatment of childhood diarrhea.
One study in Bangladeshi adults in which tetracycline was used
to treat ETEC diarrhea (determined retrospectively) showed
only a minimal effect on the severity or duration of diarrhea
Antimicrobials, however, are of definite benefit in the treat-
VOL. 18, 2005 ETEC IN DEVELOPING COUNTRIES475
ment of diarrhea of travelers, a diarrheal syndrome in which
the clinical symptom is well recognized and ETEC is known to
be the most frequent pathogen (90). It should be noted, how-
ever, that antimicrobials used for traveler’s diarrhea will treat
not only ETEC but also most of the other known causes (en-
teroaggregative E. coli, Shigella, and Campylobacter) of the
The antimicrobial treatment of traveler’s diarrhea has
changed over the years because of increasing antimicrobial
resistance (58). When ETEC were first recognized, the bacte-
ria were usually highly sensitive to all antimicrobials, including
tetracyclines and trimethoprim-sulfamethoxazole (159). How-
ever, with time, antibiotic resistance emerged, necessitating the
use of newer antimicrobials for treatment of traveler’s diar-
rhea. Antimicrobials that have been used in effective treatment
include doxycycline, trimethoprim-sulfamethoxazole, erythro-
mycin, norfloxacin, ciprofloxacin, ofloxacin, azithromycin, and
rifamycin. A summary of these studies over the years is given in
several references (58, 159). The general history of the evolv-
ing antibiotic resistance patterns in ETEC is given in Table 9.
At present, recommendations for treating ETEC can only be
stated for surety in the treatment of traveler’s diarrhea, where
ETEC are known to be the most frequent cause (51). For
adults we recommend a short course of ciprofloxacin, 500 mg
every 12 h for 1 day, which usually stops the illness within 24 h.
The new nonabsorbable antimicrobial rifaximin (50) has only
recently become available and is effective for treatment of
traveler’s diarrhea in adults, using 200 mg two times a day for
3 days. For children, we empirically recommend azithromycin,
10 mg/kg/day for 2 days, although there have been no studies to
In areas where ETEC is endemic, antimicrobial treatment is
usually not given because the diagnosis cannot be easily made
microbiologically and there are no controlled studies to pro-
Multidrug Resistance Patterns
Which antibiotic can be used has changed since the late
1970s, when doxycycline and trimethoprim-sulfamethoxazole
were the drugs of choice. Due to increasing microbial resis-
tance of ETEC, newer drugs have been used. A fluoroquino-
lone such as ciprofloxacin, levofloxacin, or ofloxacin is cur-
rently the drug of choice, since no significant resistance to
these drugs has yet developed (58, 59). A newer nonabsorbed
drug, rifaxamin, has also been shown to be as effective as a
fluoroquinolone and has only recently been approved for use
in the United States (50). Multidrug resistance is increasing in
ETEC due to the widespread use of chemotherapeutic agents
in countries where diarrhea is endemic. Antimicrobial sensi-
tivities, however, have only been studied extensively in inter-
national travelers and during common source outbreaks of
disease or specific epidemiologic studies in areas where diar-
rhea is endemic. The primary reason for this is the difficulty of
recognizing the organisms.
Although no sensitivities were reported in ETEC strains first
isolated in Calcutta in 1968, when ETEC strains were used in
volunteer studies (49), they were sensitive to ampicillin, which
was used for treatment. ETEC strains described for the first
time in Apache children in Arizona in 1971 (162) showed a
completely uniform sensitivity pattern.
Because of the high sensitivity of ETEC to doxycycline, and
because it has a long half-life and high levels in stool, this drug
was first chosen to study antibiotic prophylaxis among travelers
to developing countries (75, 111, 151). The first studies of
doxycycline prophylaxis were done in Peace Corps volunteers
in Kenya (150) and Morocco (160), who showed high degrees
of protection (?85%). In the Kenyan study (150) all ETEC
strains were sensitive to tetracycline, and only a few were
resistant to streptomycin and sulfonamide in the Moroccan
study (160). An interesting finding in these two traveler’s di-
arrhea studies (150, 160) and the study in Apaches (162) was
that nontoxigenic E. coli strains showed more antimicrobial
resistance than ETEC. This pattern was also seen in a study of
large numbers of ETEC isolated before 1978 (45), suggesting
that there may be some protective effect of harboring entero-
toxin plasmids; it was also shown that ST-producing strains
were more likely to be resistant to antimicrobials than either
LT or LT/ST strains.
In 1973, Gyles (81) found that a single conjugative plasmid
carried genes for both antibiotic resistance and enterotoxin
production, the result of recombination of an R factor with an
enterotoxin-carrying plasmid. A few years later, Echeverria
(56) found that antibiotic resistance and the ability to produce
enterotoxin were frequently transferred together and sug-
gested that the widespread use of antibiotics could result in an
increase of enterotoxigenic strains. Plasmids coding for both
antibiotic resistance and ST could be transferred in vitro to E.
coli K-12 (56) and in vivo in suckling mice, suggesting that
antibiotic selective pressure could result in a wider distribution
of ETEC (105). This hypothesis, however, has never been
A marked increase in resistance in ETEC began to be re-
ported in 1980, when it was found that during a cruise ship
outbreak the epidemic strain O25:NM was resistant to tetra-
cycline and sulfathiazole (104) and in a hospital outbreak, all
TABLE 9. Changing pattern of antimicrobial sensitivity of ETEC from its identification to the presenta
Yr and subjectsa
Sensitive to all antimicrobials (Mexico, India, U.S.A., Kenya, Morocco)
Single antibiotic resistance appears (Mexico, Bangladesh)
Multiple antimicrobial resistance appears (Tet, Amp, SXT, Doxy, Nal, Ery, S)
(Somalia, Middle East, Bangladesh)
Resistance to Cip and fluoroquinolones and multiple resistance (India, Japan)
49, 150, 154, 160
47, 48, 104, 186, 213
31, 89, 176
2001–present, T/EP31, 108
aT, travelers, including army and service personnel stationed in or visiting ETEC-endemic countries; EP, endemic population. Tet, tetracycline; Amp, ampicillin;
SXT, trimethoprim-sulfamethoxazole; nal, nalidixic acid; Ery, erythromycin; S, streptomycin; Doxy, doxycyline; Cip, ciprofloxacin.
476 QADRI ET AL.CLIN. MICROBIOL. REV.
isolates of the epidemic strain were also resistant to tetracy-
During a study of traveler’s diarrhea in Mexico, in 1989 to
1990, 49% of 74 ETEC strains were resistant to doxycycline,
9% to trimethoprim-sulfamethoxazole, 35% to ampicillin, but
none to norfloxacin or aztreonam (47) and in studies of out-
breaks of ETEC diarrhea aboard three different cruise ships
during 1997 to 1998, tetracycline resistance as high as 84%
(27/32) was reported while 30% were resistant to more than
three antimicrobials (40). This was a marked change from
previous outbreaks before 1990 when no ETEC were resistant
to more than three antimicrobials.
More recently, studies from Bangladesh and India have also
shown multiple antimicrobial resistance of ETEC isolates. A
comparison of the resistance pattern in strains isolated recently
with those obtained 30 years back highlights the increase of
resistance to commonly used drugs (48). Studies of ETEC
strains isolated between 1999 and 2001 show intermediate to
complete resistance to multiple drugs and combined resistance
to four to six drugs (including erythromycin, ampicillin, cotri-
moxazole, tetracycline, streptomycin, and doxycycline); how-
ever, not a single strain was found to be resistant to ciprofloxa-
cin. In studies in India, multidrug resistance including
resistance to nalidixic acid and to fluoroquinolones is increas-
ing (31). In Bangladesh, ETEC strains are still sensitive to
drugs which are generally used for the treatment of invasive
diarrhea, but there needs to be more awareness of changing
drug sensitivity patterns of ETEC when erythromycin is used
for treatment of acute watery diarrhea in children.
Nutritional and Micronutrient Therapy
Recently it has been found that the addition of zinc to the
therapy of diarrhea in children with diarrhea leads to shorter
duration of illness and a decrease in mortality from diarrhea
(15, 21). These studies have been done in areas of the world
where chronic zinc deficiency in children is known to occur.
Nutritional therapy for all childhood diarrheas, including
those due to ETEC, is an integral part of diarrhea treatment.
Episodes of diarrhea due to any cause, including ETEC, result
in decreased nutritional status and thus inhibit growth in chil-
dren (106). Attention to providing food, particularly breast
milk, early in the course of therapy is essential. Additional food
during and following the diarrheal episode will help in
catch-up growth (3).
Prevention of ETEC infection is clearly related to water and
sanitation, including food preparation and distribution. In the
developing world, such major improvements will be a long time
coming (57). It is estimated that it would take US$200 billion
to make the improvements necessary to prevent fecally spread
diseases in South America alone (135). Other methods on a
microscale are presently being done: building safe-water tube
wells, chlorination/filtration/heating of drinking water, and
building and improving latrines. These attempts to block trans-
mission are certainly effective if implemented but cannot solve
the problem quickly. Therefore, there is much interest in the
development of vaccines for prevention of ETEC disease.
Based on the great impact of ETEC infections on morbidity
and mortality, and probably also on nutritional status (106),
particularly of children in areas where they are endemic, an
effective ETEC vaccine is highly desirable. Such a vaccine is
feasible since epidemiologic evidence and results from exper-
imental challenge studies with human volunteers have demon-
strated that specific immunity against homologous strains fol-
lows ETEC infection. Furthermore, multiple infections with
antigenically diverse ETEC strains seem to lead to broad-
spectrum protection against ETEC diarrhea (38). Experimen-
tal studies with animals and indirect evidence from clinical
trials (191) suggest that protective immunity against ETEC is
mediated by secretory immunoglobulin A antibodies directed
against the CFs, other surface antigens, and LT; ST, which is a
small peptide, does not elicit neutralizing antibodies following
To provide broad-spectrum protection, an ETEC vaccine
should probably contain fimbrial antigens representative of the
most prevalent ETEC pathogens. The great diversity of ETEC
serotypes, with regard to both O and H antigens, makes such
antigens less attractive as vaccine components. Since CFA/I
and CS1 to CS6 are the most common human ETEC fimbriae,
they are key candidate immunogens in an ETEC vaccine.
Other fimbrial CFs may also be considered, based on their
relative importance in certain geographic areas (see Table 5).
Since a majority of ETEC strains that produce both LT and ST
or ST only produce CFs, it has been postulated that a multi-
valent ETEC vaccine containing CFA/I and CS1 to CS6 may
provide protection against approximately 50 to 80% of ETEC
strains in most geographic areas (189). If an LT toxoid such as
the nontoxic B subunit LTB or a mutant LT is included, a
multivalent toxoid-CF vaccine might provide relatively broad
protection against 80 to 90% of ETEC strains worldwide. In-
clusion of, e.g., CS7, CS12, CS14, and CS17 might expand the
potential spectrum of coverage to up to 90% of all ETEC
strains (189). A number of different strategies have been taken
to deliver fimbrial and toxin antigens of ETEC to the human
immune system to elicit protective immune responses and
functional immunological memory.
Purified CFs and Enterotoxoids
Various purified CFs have been tested as oral immunogens
but have been considered less suitable since they are expensive
to prepare and sensitive to proteolytic degradation (101). To
protect the fimbriae from degradation in the stomach, purified
CFs have been incorporated into biodegradable microspheres.
However, no significant protection was induced by any formu-
lation of purified CFs against subsequent challenge with ETEC
expressing the homologous CFs, either when immunizing with
high doses of a combination of CS1 and CS3 or recombinantly
produced CS6 (93, 101). Since LTB as well as the immunolog-
ically cross-reactive cholera toxin B subunit are strongly im-
munogenic, lack toxicity, are stable in the gastrointestinal mi-
lieu, and are capable of binding to the intestinal epithelium,
they are suitable candidate antigens to provide anti-LT immu-
nity. The cholera toxin B subunit has also afforded significant
protection against ETEC producing LT or LT/ST both in coun-
VOL. 18, 2005 ETEC IN DEVELOPING COUNTRIES477
tries where ETEC is endemic and in travelers (36, 127), but it
is possible that an LT toxoid might be slightly more effective
than cholera toxin B subunit.
An alternative administration route that has been consid-
ered is to give an ETEC vaccine by the transcutaneous route.
Such administration of E. coli CS6 together with LT has in-
duced immune responses against CS6 in about half of the
volunteers and anti-LT responses in all of them (77). Work is
in progress to evaluate E. coli LT as a candidate vaccine after
transcutaneous immunization (73).
Inactivated Whole-Cell Vaccines
Another approach that has been extensively attempted is to
immunize orally with killed ETEC bacteria that express the
most important CFs on the bacterial surface together with an
appropriate LT toxoid, i.e., cholera toxin B subunit or LTB
(189). A vaccine that consists of a combination of recombi-
nantly produced cholera toxin B subunit and formalin-inacti-
vated ETEC bacteria expressing CFA/1 and CS1 to CS5 as well
as some of the most prevalent O antigens of ETEC has been
extensively studied in clinical trials in travelers as well as in
children in areas where ETEC is endemic. This recombinant
cholera toxin B (rCTB)-CF ETEC vaccine has been shown to
be safe and gave rise to significant immunoglobulin A immune
responses in the intestine and increased levels of circulating
antibody-producing cells in a majority of adult Swedish volun-
teers (4). The vaccine has also been well tolerated and given
rise to mucosal immune responses against the different CFs of
the vaccine in 70% to 100% of volunteers of different age
groups from 18 months to 45 years in Egypt and Bangladesh
(130, 134, 169–171). However, due to an increased frequency
of vomiting in the youngest children (6 to 18 months), a re-
duced dose of the vaccine, i.e., a quarter dose that can be given
safely and with retained immunogenicity to Bangladeshi in-
fants, has been identified (129).
In an initial pilot study, the rCTB-CF ETEC vaccine was
shown to confer 82% protective efficacy (P ? 0.05) against
ETEC disease in European travelers going to 20 different
countries in Africa, Asia, and Latin America (213). However,
the number of cases fulfilling the inclusion criteria was low. In
a large placebo-controlled trial in nearly 700 American travel-
ers going to Mexico and Guatemala, the rCTB-CF ETEC
vaccine was shown to be effective (protective efficacy, 77%; P
? 0.039) against nonmild ETEC diarrheal illness, i.e., disease
that interfered with the travelers? daily activities (153, 193).
However, in a recent pediatric study in rural Egypt, the vaccine
did not confer significant protection in the 6- to 18-month-old
children tested (194).
Live Oral ETEC Vaccines
The potential of live ETEC vaccines has been suggested
based on previous findings in human volunteers that a live
vaccine strain expressing different CSs afforded highly signifi-
cant protection against challenge with wild-type ETEC ex-
pressing the corresponding CS factors (97). For example, dif-
ferent live multivalent Shigella/ETEC hybrid vaccines have
been constructed in which important fimbrial CFs are ex-
pressed along with mutated LT (10). Such vaccine candidates
have expressed CS2 and CS3 fimbriae or CFA/I, CS2, CS3, and
CS4 as well as a detoxified version of human LT (12). These
candidate vaccine strains are presently being evaluated for
safety and immunogenicity in different animal models, includ-
ing macaques. The ultimate goal is to produce five different
Shigella strains that can express the most important CFs and an
LT toxoid simultaneously in the gut.
Another approach has been to utilize attenuated ETEC
strains as vectors of key protective antigens, e.g., CS1 and CS3
(203). Evaluation of such mutated strains, PTL002 and
PTL003, in human volunteers has shown that they are safe and
immunogenic when given in a single dose.
The only vaccine that has been evaluated for protective
efficacy in a field trial in young children in areas where ETEC
is endemic so far is the rCTB-CF ETEC vaccine. Since this
vaccine did not induce significant protection in this important
target group, intense efforts should be made to improve the
immunogenicity of this or modified ETEC vaccine candidates.
As yet, no alternative ETEC vaccine is within reach to be
licensed within the next 3 to 5 years.
Based on the multitude of information presented in this
review, we make the following conclusions. ETEC is an under-
recognized but extremely important cause of diarrhea in the
developing world where there is inadequate clean water and
poor sanitation. It is the most frequent bacterial cause of di-
arrhea in infants, children, and adults living in developing
countries and the most common cause of diarrhea in interna-
tional travelers visiting these areas. ETEC diarrhea is most
frequently seen in children, suggesting that a protective im-
mune response occurs with age.
The pathogenesis of ETEC-induced diarrhea, including the
production of enterotoxins and colonization in the small intes-
tine, is similar to that of cholera. ETEC diarrhea could well be
misdiagnosed as cholera because the diseases have common
clinical syndromes and seasonalities. Treatment of ETEC di-
arrhea by rehydration is similar to that for cholera, but antibi-
otics are used routinely for ETEC only in the specific circum-
stances of traveler’s diarrhea.
The frequency and thus importance of ETEC in our under-
standing of diarrheal agents on a worldwide scale is partly
hampered by the difficulty in recognizing the organisms; no
TABLE 10. Major improvements needed
Develop simple, rapid diagnostic methods for ETEC
Set up formal reference center for testing to help standardize
procedures and make reagents available to regions where ETEC
Active screening for ETEC in diarrhea epidemics and outbreaks in
developing countries to better understand its role as a major
cause of “non-vibrio cholera”
Create awareness of the problems of ETEC diarrhea worldwide,
especially in child health programs
Direct efforts and funds directed to the development of a broad-
based multivalent ETEC vaccine
Evaluate markers of protective immunity
Design strategies to develop effective ETEC vaccines for use in
478 QADRI ET AL.CLIN. MICROBIOL. REV.
simple diagnostic tests are presently available, and identifica-
tion depends on specific reagents and technological expertise.
Like V. cholerae, ETEC is transmitted by the fecal-oral route
from contaminated food and water. Since ETEC is a multiva-
lent pathogen, it leads to repeated infections that may ad-
versely affect the nutritional status of children. Protective strat-
egies for infections are not simple, since they include
improvements in hygiene and development of effective ETEC
vaccines. Although antimicrobials are not used routinely in
treatment of children with ETEC diarrhea, the emerging prob-
lem of multiple antimicrobial resistance will definitely affect
the drugs used for traveler’s diarrhea. Serious efforts need to
be made to improve the awareness of the importance of ETEC,
particularly on the health of infants and children living in the
developing world (Table 10).
This work was supported by the International Centre for Diarrheal
Disease Research, Bangladesh (ICDDR, B), Centre for Health and
Population Research. We acknowledge with gratitude the commitment
of the National Institute of Allergy and Infectious Disease (NIH grant
AI39129) and the Swedish Agency for Research and Economic Coop-
eration (Sida-SAREC, grant no. 2001-3970) to the Centre’s research
1. Abu-Elyazeed, R., T. F. Wierzba, A. S. Mourad, L. F. Peruski, B. A. Kay, M.
Rao, A. M. Churilla, A. L. Bourgeois, A. K. Mortagy, S. M. Kamal, S. J.
Savarino, J. R. Campbell, J. R. Murphy, A. Naficy, and J. D. Clemens. 1999.
Epidemiology of enterotoxigenic Escherichia coli diarrhea in a pediatric
cohort in a periurban area of lower Egypt. J. Infect. Dis. 179:382–389.
2. Adachi, J. A., J. J. Mathewson, Z. D. Jiang, C. D. Ericsson, and H. L.
DuPont. 2002. Enteric pathogens in Mexican sauces of popular restaurants
in Guadalajara, Mexico, and Houston, Texas. Ann. Intern. Med. 136:884–
3. Ahmed, T., M. Ali, M. M. Ullah, I. A. Choudhury, M. E. Haque, M. A.
Salam, G. H. Rabbani, R. M. Suskind, and G. J. Fuchs. 1999. Mortality in
severely malnourished children with diarrhoea and use of a standardised
management protocol. Lancet 353:1919–1922.
4. Ahren, C., M. Jertborn, and A. M. Svennerholm. 1998. Intestinal immune
responses to an inactivated oral enterotoxigenic Escherichia coli vaccine and
associated immunoglobulin A responses in blood. Infect. Immun. 66:3311–
5. Ahren, C. M., L. Gothefors, B. J. Stoll, M. A. Salek, and A. M. Svenner-
holm. 1986. Comparison of methods for detection of colonization factor
antigens on enterotoxigenic Escherichia coli. J. Clin. Microbiol. 23:586–591.
6. Alam, N. H., and H. Ashraf. 2003. Treatment of infectious diarrhea in
children. Paediatr. Drugs 5:151–165.
7. Albert, M. J., A. S. Faruque, S. M. Faruque, R. B. Sack, and D. Ma-
halanabis. 1999. Case-control study of enteropathogens associated with
childhood diarrhea in Dhaka, Bangladesh. J. Clin. Microbiol. 37:3458–3464.
8. Albert, M. J., S. M. Faruque, A. S. Faruque, P. K. Neogi, M. Ansaruzzaman,
N. A. Bhuiyan, K. Alam, and M. S. Akbar. 1995. Controlled study of
Escherichia coli diarrheal infections in Bangladeshi children. J. Clin. Mi-
9. Albert, M. J., F. Qadri, M. A. Wahed, T. Ahmed, A. S. Rahman, F. Ahmed,
N. A. Bhuiyan, K. Zaman, A. H. Baqui, J. D. Clemens, and R. E. Black.
2003. Supplementation with zinc, but not vitamin A, improves seroconver-
sion to vibriocidal antibody in children given an oral cholera vaccine. J. In-
fect. Dis. 187:909–913.
10. Altboum, Z., E. M. Barry, G. Losonsky, J. E. Galen, and M. M. Levine.
2001. Attenuated Shigella flexneri 2a Delta guaBA strain CVD 1204 ex-
pressing enterotoxigenic Escherichia coli (ETEC) CS2 and CS3 fimbriae as
a live mucosal vaccine against Shigella and ETEC infection. Infect. Immun.
11. Baqui, A. H., R. B. Sack, R. E. Black, K. Haider, A. Hossain, A. R. Alim, M.
Yunus, H. R. Chowdhury, and A. K. Siddique. 1992. Enteropathogens
associated with acute and persistent diarrhea in Bangladeshi children less
than 5 years of age. J. Infect. Dis. 166:792–796.
12. Barry, E. M., Z. Altboum, G. Losonsky, and M. M. Levine. 2003. Immune
responses elicited against multiple enterotoxigenic Escherichia coli fimbriae
and mutant LT expressed in attenuated Shigella vaccine strains. Vaccine
13. Begaud, E., P. Jourand, M. Morillon, D. Mondet, and Y. Germani. 1993.
Detection of diarrheogenic Escherichia coli in children less than ten years
old with and without diarrhea in New Caledonia using seven acetylamin-
ofluorene-labeled DNA probes. Am. J. Trop. Med. Hyg. 48:26–34.
14. Begum, Y. A., K. A. Talukder, G. B. Nair, A. M. Svennerholm, R. B. Sack,
and F. Qadri. Enterotoxigenic Escherichia coli isolated from surface water
in urban and rural Bangladesh. J. Clin. Microbiol., in press.
15. Bhandari, N., R. Bahl, S. Taneja, T. Strand, K. Molbak, R. J. Ulvik, H.
Sommerfelt, and M. K. Bhan. 2002. Substantial reduction in severe diar-
rheal morbidity by daily zinc supplementation in young north Indian chil-
dren. Pediatrics 109:e86.
16. Binsztein, N., M. J. Jouve, G. I. Viboud, L. Lopez Moral, M. Rivas, I.
Orskov, C. Ahren, and A. M. Svennerholm. 1991. Colonization factors of
enterotoxigenic Escherichia coli isolated from children with diarrhea in
Argentina. J. Clin. Microbiol. 29:1893–1898.
17. Black, R. E. 1993. Epidemiology of diarrhoeal disease: implications for
control by vaccines. Vaccine 11:100–106.
18. Black, R. E. 1990. Epidemiology of travelers’ diarrhea and relative impor-
tance of various pathogens. Rev. Infect. Dis. 12(Suppl. 1):S73–S79.
19. Black, R. E. 1993. Persistent diarrhea in children of developing countries.
Pediatr. Infect. Dis. J. 12:751–764.
20. Black, R. E. 1990. Prevention in developing countries. J. Gen. Intern. Med.
21. Black, R. E. 2003. Zinc deficiency, infectious disease and mortality in the
developing world. J. Nutr. 133:1485S–9S.
22. Black, R. E., K. H. Brown, and S. Becker. 1984. Effects of diarrhea associ-
ated with specific enteropathogens on the growth of children in rural Ban-
gladesh. Pediatrics 73:799–805.
23. Black, R. E., G. Lopez de Romana, K. H. Brown, N. Bravo, O. G. Bazalar,
and H. C. Kanashiro. 1989. Incidence and etiology of infantile diarrhea and
major routes of transmission in Huascar, Peru. Am. J. Epidemiol. 129:785–
24. Black, R. E., M. H. Merson, I. Huq, A. R. Alim, and M. Yunus. 1981.
Incidence and severity of rotavirus and Escherichia coli diarrhoea in rural
Bangladesh. Implications for vaccine development. Lancet i:141–143.
25. Black, R. E., M. H. Merson, B. Rowe, P. R. Taylor, A. R. Abdul Alim, R. J.
Gross, and D. A. Sack. 1981. Enterotoxigenic Escherichia coli diarrhoea:
acquired immunity and transmission in an endemic area. Bull. W.H.O.
26. Blanco, J. E., M. Blanco, and J. Blanco. 1995. [Enterotoxigenic, verotoxi-
genic, and necrotoxigenic Escherichia coli in food and clinical samples.
Role of animals as reservoirs of strains pathogenic for humans]. Microbio-
27. Bray, J. 1945. Isolation of antigenically homogeneous strains of Bact coli
neapolitanum from summer diarrhoea of infants. J. Pathol. Bacteriol. 57:
28. Brown, K. H. 2003. Diarrhea and malnutrition. J. Nutr. 133:328S–332S.
29. Caeiro, J. P., M. T. Estrada-Garcia, Z. D. Jiang, J. J. Mathewson, J. A.
Adachi, R. Steffen, and H. L. DuPont. 1999. Improved detection of ente-
rotoxigenic Escherichia coli among patients with travelers’ diarrhea, by use
of the polymerase chain reaction technique. J. Infect. Dis. 180:2053–2055.
30. Carpenter, C. C., D. Barua, C. K. Wallace, R. B. Sack, P. P. Mitra, A. S.
Werner, T. P. Duffy, A. Oleinick, S. R. Khanra, and G. W. Lewis. 1965.
Clinical and physiological observations during an epidemic outbreak of
non-vibrio cholera-like disease in Calcutta. Bull. W.H.O. 33:665–671.
31. Chakraborty, S., J. S. Deokule, P. Garg, S. K. Bhattacharya, R. K. Nandy,
G. B. Nair, S. Yamasaki, Y. Takeda, and T. Ramamurthy. 2001. Concom-
itant infection of enterotoxigenic Escherichia coli in an outbreak of cholera
caused by Vibrio cholerae O1 and O139 in Ahmedabad, India. J. Clin.
32. Chapman, P. A., and C. M. Daly. 1993. Evaluation of non-radioactive
trivalent DNA probe (LT, ST1a, ST1b) for detecting enterotoxigenic Esch-
erichia coli. J. Clin. Pathol. 46:309–312.
33. Clemens, J., S. Savarino, R. Abu-Elyazeed, M. Safwat, M. Rao, T. Wierzba,
A. M. Svennerholm, J. Holmgren, R. Frenck, E. Park, and A. Naficy. 2004.
Development of pathogenicity-driven definitions of outcomes for a field
trial of a killed oral vaccine against enterotoxigenic Escherichia coli in
Egypt: application of an evidence-based method. J. Infect. Dis. 189:2299–
34. Clemens, J. D., M. R. Rao, J. Chakraborty, M. Yunus, M. Ali, B. Kay,
F. P. L. van Loon, A. Naficy, and D. A. Sack. 1997. Breastfeeding and the
risk of life-threatening enterotoxigenic Escherichia coli diarrhea in Bang-
ladeshi infants and children. Pediatrics 100:E2.
35. Clemens, J. D., D. A. Sack, J. Chakraborty, M. R. Rao, F. Ahmed, J. R.
Harris, F. van Loon, M. R. Khan, M. Yunis, S. Huda, et al. 1990. Field trial
of oral cholera vaccines in Bangladesh: evaluation of anti-bacterial and
anti-toxic breast-milk immunity in response to ingestion of the vaccines.
36. Clemens, J. D., D. A. Sack, J. R. Harris, J. Chakraborty, P. K. Neogy, B.
Stanton, N. Huda, M. U. Khan, B. A. Kay, M. R. Khan, et al. 1988.
Cross-protection by B subunit-whole cell cholera vaccine against diarrhea
associated with heat-labile toxin-producing enterotoxigenic Escherichia
coli: results of a large-scale field trial. J. Infect. Dis. 158:372–377.
VOL. 18, 2005ETEC IN DEVELOPING COUNTRIES479
37. Cravioto, A., R. E. Reyes, R. Ortega, G. Fernandez, R. Hernandez, and D.
Lopez. 1988. Prospective study of diarrhoeal disease in a cohort of rural
Mexican children: incidence and isolated pathogens during the first two
years of life. Epidemiol. Infect. 101:123–134.
38. Cravioto, A., R. E. Reyes, F. Trujillo, F. Uribe, A. Navarro, J. M. De La
Roca, J. M. Hernandez, G. Perez, and V. Vazquez. 1990. Risk of diarrhea
during the first year of life associated with initial and subsequent coloniza-
tion by specific enteropathogens. Am. J. Epidemiol. 131:886–904.
39. Cruz, J. R., F. Cano, and P. Caceres. 1991. Association of human milk SIgA
antibodies with maternal intestinal exposure to microbial antigens. Adv.
Exp. Med. Biol. 310:193–199.
40. Daniels, N. A., J. Neimann, A. Karpati, U. D. Parashar, K. D. Greene, J. G.
Wells, A. Srivastava, R. V. Tauxe, E. D. Mintz, and R. Quick. 2000. Trav-
eler’s diarrhea at sea: three outbreaks of waterborne enterotoxigenic Esch-
erichia coli on cruise ships. J. Infect. Dis. 181:1491–1495.
41. Danielsson, M. L., R. Mollby, H. Brag, N. Hansson, P. Jonsson, E. Olsson,
and T. Wadstrom. 1979. Enterotoxigenic enteric bacteria in foods and
outbreaks of food-borne diseases in Sweden. J. Hyg. (London) 83:33–40.
42. Darfeuille-Michaud, A., D. Aubel, G. Chauviere, C. Rich, M. Bourges, A.
Servin, and B. Joly. 1990. Adhesion of enterotoxigenic Escherichia coli to
the human colon carcinoma cell line Caco-2 in culture. Infect. Immun.
43. De, S. N., K. Bhattacharya, and J. K. Sarkar. 1956. A study of the patho-
genicity of strains of Bacterium coli from acute and chronic enteritis.
J. Pathol. Bacteriol. 71:201–209.
44. Dean, A. G., Y. C. Ching, R. G. Williams, and L. B. Harden. 1972. Test for
Escherichia coli enterotoxin using infant mice: application in a study of
diarrhea in children in Honolulu. J. Infect. Dis. 125:407–411.
45. DeBoy, J. M., 2nd, I. K. Wachsmuth, and B. R. Davis. 1980. Antibiotic
resistance in enterotoxigenic and non-enterotoxigenic Escherichia coli.
J. Clin. Microbiol. 12:264–270.
46. Donta, S. T., and D. M. Smith. 1974. Stimulation of steroidogenesis in
tissue culture by enterotoxigenic Escherichia coli and its neutralization by
specific antiserum. Infect. Immun. 9:500–505.
47. DuPont, H. L., C. D. Ericsson, J. J. Mathewson, F. J. de la Cabada, and
D. A. Conrad. 1992. Oral aztreonam, a poorly absorbed yet effective therapy
for bacterial diarrhea in US travelers to Mexico. JAMA 267:1932–1935.
48. DuPont, H. L., D. G. Evans, D. J. Evans, Jr., and T. K. Satterwhite. 1981.
Antitoxic immunity in cholera and enterotoxigenic Escherichia coli (ETEC)
diarrhea. Pharmacol. Ther. 13:249–255.
49. DuPont, H. L., S. B. Formal, R. B. Hornick, M. J. Snyder, J. P. Libonati,
D. G. Sheahan, E. H. LaBrec, and J. P. Kalas. 1971. Pathogenesis of
Escherichia coli diarrhea. N. Engl. J. Med. 285:1–9.
50. DuPont, H. L., Z. D. Jiang, C. D. Ericsson, J. A. Adachi, J. J. Mathewson,
M. W. DuPont, E. Palazzini, L. M. Riopel, D. Ashley, and F. Martinez-
Sandoval. 2001. Rifaximin versus ciprofloxacin for the treatment of travel-
er’s diarrhea: a randomized, double-blind clinical trial. Clin. Infect. Dis.
51. Dupont, H. L., and L. Mattila. 2003. Antimicrobial treatment: an algorith-
mic approach, p. 227–237. In C. D. Ericsson et al. (ed.), Travelers’ diarrhea.
BC Decker Inc., Hamilton, Canada.
52. Echeverria, P., C. Pitarangsi, B. Eampokalap, S. Vibulbandhitkit, P.
Boonthai, and B. Rowe. 1983. A longitudinal study of the prevalence of
bacterial enteric pathogens among adults with diarrhea in Bangkok, Thai-
land. Diagn. Microbiol. Infect. Dis. 1:193–204.
53. Echeverria, P., J. Seriwatana, O. Chityothin, W. Chaicumpa, and C. Ti-
rapat. 1982. Detection of enterotoxigenic Escherichia coli in water by filter
hybridization with three enterotoxin gene probes. J. Clin. Microbiol. 16:
54. Echeverria, P., J. Seriwatana, U. Leksomboon, C. Tirapat, W. Chaicumpa,
and B. Rowe. 1984. Identification by DNA hybridisation of enterotoxigenic
Escherichia coli in homes of children with diarrhoea. Lancet 1:63–66.
55. Echeverria, P., D. N. Taylor, U. Lexsomboon, M. Bhaibulaya, N. R. Black-
low, K. Tamura, and R. Sakazaki. 1989. Case-control study of endemic
diarrheal disease in Thai children. J. Infect. Dis. 159:543–548.
56. Echeverria, P., L. Verhaert, C. V. Ulyangco, S. Komalarini, M. T. Ho, F.
Orskov, and I. Orskov. 1978. Antimicrobial resistance and enterotoxin
production among isolates of Escherichia coli in the Far East. Lancet
57. Editorial. 2004. Clean water alone cannot prevent disease. Lancet 364:816.
58. Ericsson, C. D. 2003. Travellers’ diarrhoea. Int. J. Antimicrob. Agents
59. Ericsson, C. D., H. L. DuPont, and J. J. Mathewson. 1997. Single dose
ofloxacin plus loperamide compared with single dose or three days of
ofloxacin in the treatment of traveler’s diarrhea. J. Travel Med. 4:3–7.
60. Evans, D. G., D. J. Evans, Jr., W. S. Tjoa, and H. L. DuPont. 1978.
Detection and characterization of colonization factor of enterotoxigenic
Escherichia coli isolated from adults with diarrhea. Infect. Immun. 19:727–
61. Evans, D. J., Jr., and D. G. Evans. 1973. Three characteristics associated
with enterotoxigenic Escherichia coli isolated from man. Infect. Immun.
62. Faruque, A. S., M. A. Malek, A. I. Khan, S. Huq, M. A. Salam, and D. A.
Sack. 2004. Diarrhoea in elderly people: aetiology, and clinical character-
istics. Scand J. Infect. Dis. 36:204–208.
63. Faruque, A. S., M. A. Salam, S. M. Faruque, and G. J. Fuchs. 1998.
Aetiological, clinical and epidemiological characteristics of a seasonal peak
of diarrhoea in Dhaka, Bangladesh. Scand J. Infect. Dis. 30:393–396.
64. Freedman, D. J., C. O. Tacket, A. Delehanty, D. R. Maneval, J. Nataro, and
J. H. Crabb. 1998. Milk immunoglobulin with specific activity against pu-
rified colonization factor antigens can protect against oral challenge with
enterotoxigenic Escherichia coli. J. Infect. Dis. 177:662–667.
65. Gaastra, W., and F. K. de Graaf. 1982. Host-specific fimbrial adhesins of
noninvasive enterotoxigenic Escherichia coli strains. Microbiol. Rev. 46:
66. Gaastra, W., and A. M. Svennerholm. 1996. Colonization factors of human
enterotoxigenic Escherichia coli (ETEC). Trends Microbiol. 4:444–452.
67. Geyer, A., H. H. Crewe-Brown, A. S. Greeff, P. J. Fripp, A. D. Steele, T. V.
Van Schalkwyk, and C. G. Clay. 1993. The microbial aetiology of summer
paediatric gastroenteritis at Ga-Rankuwa Hospital in South Africa. East
Afr. Med. J. 70:78–81.
68. Giannella, R. A., K. W. Drake, and M. Luttrell. 1981. Development of a
radioimmunoassay for Escherichia coli heat-stable enterotoxin: comparison
with the suckling mouse bioassay. Infect. Immun. 33:186–192.
69. Gibbons, R. A., R. Sellwood, M. Burrows, et al. 1977. Inheritance of resis-
tance to neonatal Escherichia coli diarrhea in the pig: examination of the
genetic system. Theor. Appl. Genet 51:65–70.
70. Gill, D. M., and S. H. Richardson. 1980. Adenosine diphosphate-ribosyla-
tion of adenylate cyclase catalyzed by heat-labile enterotoxin of Escherichia
coli: comparison with cholera toxin. J. Infect. Dis. 141:64–70.
71. Giugliani, E. R., and C. G. Victoria. 2000. [Complementary feeding]. J. Pe-
diatr. (Rio. J.) 76(Suppl. 3):S253–262.
72. Glass, R. I., A. M. Svennerholm, B. J. Stoll, M. R. Khan, K. M. Hossain,
M. I. Huq, and J. Holmgren. 1983. Protection against cholera in breast-fed
children by antibodies in breast milk. N. Engl. J. Med. 308:1389–1392.
73. Glenn, G. M., D. N. Taylor, X. Li, S. Frankel, A. Montemarano, and C. R.
Alving. 2000. Transcutaneous immunization: a human vaccine delivery
strategy using a patch. Nat. Med. 6:1403–1406.
74. Gorbach, S. L., J. G. Banwell, B. D. Chatterjee, B. Jacobs, and R. B. Sack.
1971. Acute undifferentiated human diarrhea in the tropics. I. Alterations
in intestinal micrflora. J. Clin. Investig. 50:881–889.
75. Gorbach, S. L., B. H. Kean, D. G. Evans, D. J. Evans, Jr., and D. Bessudo.
1975. Travelers’ diarrhea and toxigenic Escherichia coli. N. Engl. J. Med.
76. Gothefors, L., C. Ahren, B. Stoll, D. K. Barua, F. Orskov, M. A. Salek, and
A. M. Svennerholm. 1985. Presence of colonization factor antigens on fresh
isolates of fecal Escherichia coli: a prospective study. J. Infect. Dis. 152:
77. Guerena-Burgueno, F., E. R. Hall, D. N. Taylor, F. J. Cassels, D. A. Scott,
M. K. Wolf, Z. J. Roberts, G. V. Nesterova, C. R. Alving, and G. M. Glenn.
2002. Safety and immunogenicity of a prototype enterotoxigenic Escherichia
coli vaccine administered transcutaneously. Infect. Immun. 70:1874–1880.
78. Guerrant, R. L., L. L. Brunton, T. C. Schnaitman, L. I. Rebhun, and A. G.
Gilman. 1974. Cyclic adenosine monophosphate and alteration of Chinese
hamster ovary cell morphology: a rapid, sensitive in vitro assay for the
enterotoxins of Vibrio cholerae and Escherichia coli. Infect. Immun. 10:320–
79. Guerrant, R. L., L. V. Kirchhoff, D. S. Shields, M. K. Nations, J. Leslie,
M. A. de Sousa, J. G. Araujo, L. L. Correia, K. T. Sauer, K. E. McClelland,
et al. 1983. Prospective study of diarrheal illnesses in northeastern Brazil:
patterns of disease, nutritional impact, etiologies, and risk factors. J. Infect.
80. Gyles, C. L., and D. A. Barnum. 1969. A heat-labile enterotoxin from strains
of Eschericha coli enteropathogenic for pigs. J. Infect. Dis. 120:419–426.
81. Gyles, C. L., S. Palchaudhuri, and W. K. Maas. 1977. Naturally occurring
plasmid carrying genes for enterotoxin production and drug resistance.
82. Hill, W. E., J. M. Madden, B. A. McCardell, D. B. Shah, J. A. Jagow, W. L.
Payne, and B. K. Boutin. 1983. Foodborne enterotoxigenic Escherichia coli:
detection and enumeration by DNA colony hybridization. Appl. Environ.
83. Holmgren, J. 1981. Actions of cholera toxin and the prevention and treat-
ment of cholera. Nature 292:413–417.
84. Holmgren, J., L. A. Hanson, B. Carlson, B. S. Lindblad, and J. Rahimtoola.
1976. Neutralizing antibodies against Escherichia coli and Vibrio cholerae
enterotoxins in human milk from a developing country. Scand. J. Immunol.
85. Holmgren, J., A. M. Svennerholm, and M. Lindblad. 1983. Receptor-like
glycocompounds in human milk that inhibit classical and El Tor Vibrio
cholerae cell adherence (hemagglutination). Infect. Immun. 39:147–154.
86. Honda, T., Q. Akhtar, R. I. Glass, and A. K. Kibriya. 1981. A simple assay
to detect Escherichia coli producing heat labile enterotoxin: results of a
field study of the Biken tests in Bangladesh. Lancet ii:609–610.
87. Huerta, M., I. Grotto, M. Gdalevich, D. Mimouni, B. Gavrieli, M. Yavzori,
480QADRI ET AL.CLIN. MICROBIOL. REV.
D. Cohen, and O. Shpilberg. 2000. A waterborne outbreak of gastroenteritis
in the Golan Heights due to enterotoxigenic Escherichia coli. Infection
88. Huilan, S., L. G. Zhen, M. M. Mathan, M. M. Mathew, J. Olarte, R. Espejo,
U. Khin Maung, M. A. Ghafoor, M. A. Khan, Z. Sami, et al. 1991. Etiology
of acute diarrhoea among children in developing countries: a multicentre
study in five countries. Bull. W.H.O. 69:549–555.
89. Hyams, K. C., A. L. Bourgeois, B. R. Merrell, P. Rozmajzl, J. Escamilla,
S. A. Thornton, G. M. Wasserman, A. Burke, P. Echeverria, K. Y. Green, et
al. 1991. Diarrheal disease during Operation Desert Shield. N. Engl.
J. Med. 325:1423–1428.
90. Jiang, Z. D., B. Lowe, M. P. Verenkar, D. Ashley, R. Steffen, N. Tornieporth,
F. von Sonnenburg, P. Waiyaki, and H. L. DuPont. 2002. Prevalence of
enteric pathogens among international travelers with diarrhea acquired in
Kenya (Mombasa), India (Goa), or Jamaica (Montego Bay). J. Infect. Dis.
91. Karlsen, T. H., H. Sommerfelt, S. Klomstad, P. K. Andersen, T. A. Strand,
R. J. Ulvik, C. Ahren, and H. M. Grewal. 2003. Intestinal and systemic
immune responses to an oral cholera toxoid B subunit whole-cell vaccine
administered during zinc supplementation. Infect. Immun. 71:3909–3913.
92. Karmali, M. A. 1998. The nature of immunity to the Escherichia coli Shiga
toxins (verocytotoxins) and options for toxoid immunization. Jpn. J. Med.
Sci. Biol. 51(Suppl.):S26–35.
93. Katz, D. E., A. J. DeLorimier, M. K. Wolf, E. R. Hall, F. J. Cassels, J. E. van
Hamont, R. L. Newcomer, M. A. Davachi, D. N. Taylor, and C. E. McQueen.
2003. Oral immunization of adult volunteers with microencapsulated ente-
rotoxigenic Escherichia coli (ETEC) CS6 antigen. Vaccine 21:341–346.
94. Khan, M. U., R. Eeckels, A. N. Alam, and N. Rahman. 1988. Cholera,
rotavirus and ETEC diarrhoea: some clinico-epidemiological features.
Trans. R. Soc. Trop. Med. Hyg. 82:485–488.
95. King, C. K., R. Glass, J. S. Bresee, and C. Duggan. 2003. Managing acute
gastroenteritis among children: oral rehydration, maintenance, and nutri-
tional therapy. Morb. Mortal. Wkly. Rep. Recomm. Rep. 52:1–16.
96. Kosek, M., C. Bern, and R. L. Guerrant. 2003. The global burden of
diarrhoeal disease, as estimated from studies published between 1992 and
2000. Bull. W.H.O. 81:197–204.
97. Levine, M. M. 1990. Modern vaccines. Enteric infections. Lancet 335:958–
98. Levine, M. M., E. J. Bergquist, D. R. Nalin, D. H. Waterman, R. B. Hornick,
C. R. Young, and S. Sotman. 1978. Escherichia coli strains that cause
diarrhoea but do not produce heat-labile or heat-stable enterotoxins and
are non-invasive. Lancet i:1119–1122.
99. Levine, M. M., C. Ferreccio, V. Prado, M. Cayazzo, P. Abrego, J. Martinez,
L. Maggi, M. M. Baldini, W. Martin, D. Maneval, et al. 1993. Epidemio-
logic studies of Escherichia coli diarrheal infections in a low socioeconomic
level peri-urban community in Santiago, Chile. Am. J. Epidemiol. 138:849–
100. Levine, M. M., D. R. Nalin, D. L. Hoover, E. J. Bergquist, R. B. Hornick,
and C. R. Young. 1979. Immunity to enterotoxigenic Escherichia coli. Infect.
101. Levine, M. M., and A. M. Svennerholm. 2001. Enteric vaccines: present and
future, 2nd ed. BC Decker, New York, NY.
102. Long, K. Z., J. W. Wood, E. Vasquez Gariby, K. M. Weiss, J. J. Mathewson,
F. J. de la Cabada, H. L. DuPont, and R. A. Wilson. 1994. Proportional
hazards analysis of diarrhea due to enterotoxigenic Escherichia coli and
breast feeding in a cohort of urban Mexican children. Am. J. Epidemiol.
103. Lopez-Vidal, Y., J. J. Calva, A. Trujillo, A. Ponce de Leon, A. Ramos, A. M.
Svennerholm, and G. M. Ruiz-Palacios. 1990. Enterotoxins and adhesins of
enterotoxigenic Escherichia coli: are they risk factors for acute diarrhea in
the community? J. Infect. Dis. 162:442–447.
104. Lumish, R. M., R. W. Ryder, D. C. Anderson, J. G. Wells, and N. D. Puhr.
1980. Heat-labile enterotoxigenic Escherichia coli induced diarrhea aboard
a Miami-based cruise ship. Am. J. Epidemiol. 111:432–436.
105. Martinez, L. Y., M. M. Arenas, M. Y. Montes, L. J. Martinez, and B. E.
Baca. 1987. Antibiotic resistance and plasmid pattern of enterotoxigenic
ST-a strains of Escherichia coli isolated in Puebla, Mexico. Can. J. Micro-
106. Mata, L. 1992. Diarrheal disease as a cause of malnutrition. Am. J. Trop.
Med. Hyg. 47:16–27.
107. Mathur, R., V. Reddy, A. N. Naidu, Ravikumar, and K. A. Krishnamachari.
1985. Nutritional status and diarrhoeal morbidity: a longitudinal study in
rural Indian preschool children. Hum. Nutr. Clin. Nutr. 39:447–454.
108. Matsushita, S., M. Kawamura, M. Takahashi, K. Yokoyama, N. Konishi, K.
Hatakeyama, A. Kai, S. Morozumi, K. Morita, N. Watanabe, M. Kanamori,
and Y. Kudoh. 2001. [Increasing fluoroquinolone low-sensitivity in entero-
toxigenic Escherichia coli isolated from diarrhea of overseas travelers in
Tokyo]. Kansenshogaku Zasshi 75:785–791.
109. Mattila, L., A. Siitonen, H. Kyronseppa, I. Simula, P. Oksanen, M. Stenvik,
P. Salo, and H. Peltola. 1992. Seasonal variation in etiology of travelers’
diarrhea. Finnish-Moroccan Study Group. J. Infect. Dis. 165:385–388.
110. McConnell, M. M., M. L. Hibberd, M. E. Penny, S. M. Scotland, T. Cheasty,
and B. Rowe. 1991. Surveys of human enterotoxigenic Escherichia coli from
three different geographical areas for possible colonization factors. Epide-
miol. Infect. 106:477–484.
111. Merson, M. H., G. K. Morris, D. A. Sack, J. G. Wells, J. C. Feeley, R. B.
Sack, W. B. Creech, A. Z. Kapikian, and E. J. Gangarosa. 1976. Travelers’
diarrhea in Mexico. A prospective study of physicians and family members
attending a congress. N. Engl. J. Med. 294:1299–1305.
112. Merson, M. H., F. Orskov, I. Orskov, R. B. Sack, I. Huq, and F. T. Koster.
1979. Relationship between enterotoxin production and serotype in ente-
rotoxigenic Escherichia coli. Infect. Immun. 23:325–329.
113. Merson, M. H., R. B. Sack, S. Islam, G. Saklayen, N. Huda, I. Huq, A. W.
Zulich, R. H. Yolken, and A. Z. Kapikian. 1980. Disease due to enterotoxi-
genic Escherichia coli in Bangladeshi adults: clinical aspects and a con-
trolled trial of tetracycline. J. Infect. Dis. 141:702–711.
114. Molla, A. M., M. Rahman, S. A. Sarker, D. A. Sack, and A. Molla. 1981.
Stool electrolyte content and purging rates in diarrhea caused by rotavirus,
enterotoxigenic E. coli, and V. cholerae in children. J. Pediatr. 98:835–838.
115. Nagy, B., and P. Z. Fekete. 1999. Enterotoxigenic Escherichia coli (ETEC)
in farm animals. Vet. Res. 30:259–284.
116. Nair, G. B., and Y. Takeda. 1998. The heat-stable enterotoxins. Microb.
117. Nalin, D. R., J. C. McLaughlin, M. Rahaman, M. Yunus, and G. Curlin.
1975. Enterotoxigenic Escherichia coli and idiopathic diarrhoea in Bang-
ladesh. Lancet ii:1116–1119.
118. Nataro, J. P., and J. B. Kaper. 1998. Diarrheagenic Escherichia coli. Clin.
Microbiol. Rev. 11:142–201.
119. Nicklasson, M., A. Sjoling, G. Wiklund, and A. M. Svennerholm. 2004.
Molecular genetics of bacteria and phages, p. 135. Cold Spring Harbor
Laboratory, Cold Spring Harbor, NY.
120. Nirdnoy, W., O. Serichantalergs, A. Cravioto, C. LeBron, M. Wolf, C. W.
Hoge, A. M. Svennerholm, D. N. Taylor, and P. Echeverria. 1997. Distri-
bution of colonization factor antigens among enterotoxigenic Escherichia
coli strains isolated from patients with diarrhea in Nepal, Indonesia, Peru,
and Thailand. J. Clin. Microbiol. 35:527–530.
121. Ohno, A., A. Marui, E. S. Castro, A. A. Reyes, D. Elio-Calvo, H. Kasitani,
Y. Ishii, and K. Yamaguchi. 1997. Enteropathogenic bacteria in the La Paz
River of Bolivia. Am. J. Trop. Med. Hyg. 57:438–444.
122. Olsvik, O., Y. Wasteson, A. Lund, and E. Hornes. 1991. Pathogenic Esch-
erichia coli found in food. Int. J. Food Microbiol. 12:103–113.
123. Olsvik, Q., and, S. N. A. 1993. PCR detection of heat-stable, heat-labile,
and Shiga-like toxin genes in Escherichia coli, p. 271–276. In Diagnostic
molecular microbiology. American Society for Microbiology, Washington,
124. Orskov, F., I. Orskov, D. J. Evans, Jr., R. B. Sack, D. A. Sack, and T.
Wadstrom. 1976. Special Escherichia coli serotypes among enterotoxigenic
strains from diarrhoea in adults and children. Med. Microbiol. Immunol.
125. Pacheco, A. B., B. E. Guth, K. C. Soares, L. Nishimura, D. F. de Almeida,
and L. C. Ferreira. 1997. Random amplification of polymorphic DNA
reveals serotype-specific clonal clusters among enterotoxigenic Escherichia
coli strains isolated from humans. J. Clin. Microbiol. 35:1521–1525.
126. Paniagua, M., F. Espinoza, M. Ringman, E. Reizenstein, A. M. Svenner-
holm, and H. Hallander. 1997. Analysis of incidence of infection with
enterotoxigenic Escherichia coli in a prospective cohort study of infant
diarrhea in Nicaragua. J. Clin. Microbiol. 35:1404–1410.
127. Peltola, H., A. Siitonen, H. Kyronseppa, I. Simula, L. Mattila, P. Oksanen,
M. J. Kataja, and M. Cadoz. 1991. Prevention of travellers’ diarrhoea by
oral B-subunit/whole-cell cholera vaccine. Lancet 338:1285–1289.
128. Peruski, L. F., Jr., B. A. Kay, R. A. El-Yazeed, S. H. El-Etr, A. Cravioto,
T. F. Wierzba, M. Rao, N. El-Ghorab, H. Shaheen, S. B. Khalil, K. Kamal,
M. O. Wasfy, A. M. Svennerholm, J. D. Clemens, and S. J. Savarino. 1999.
Phenotypic diversity of enterotoxigenic Escherichia coli strains from a com-
munity-based study of pediatric diarrhea in periurban Egypt. J. Clin. Mi-
129. Qadri, F., T. Ahmed, F. Ahmed, Y. A. Begum, D. A. Sack, and A. M.
Svennerholm. 2003. Presented at the 10th Asian Conference on Diarrhoeal
Diseases and Nutrition, Dhaka, Bangladesh, 7 to 9 December.
130. Qadri, F., T. Ahmed, F. Ahmed, R. Bradley Sack, D. A. Sack, and A. M.
Svennerholm. 2003. Safety and immunogenicity of an oral, inactivated en-
terotoxigenic Escherichia coli plus cholera toxin B subunit vaccine in Ban-
gladeshi children 18–36 months of age. Vaccine 21:2394–2403.
131. Qadri, F., T. Ahmed, M. A. Wahed, F. Ahmed, N. A. Bhuiyan, A. S. Rah-
man, J. D. Clemens, R. E. Black, and M. J. Albert. 2004. Suppressive effect
of zinc on antibody response to cholera toxin in children given the killed, B
subunit-whole cell, oral cholera vaccine. Vaccine 22:416–421.
132. Qadri, F., S. K. Das, A. S. Faruque, G. J. Fuchs, M. J. Albert, R. B. Sack,
and A. M. Svennerholm. 2000. Prevalence of toxin types and colonization
factors in enterotoxigenic Escherichia coli isolated during a 2-year period
from diarrheal patients in Bangladesh. J. Clin. Microbiol. 38:27–31.
133. Qadri, F., J. A. Giron, A. Helander, Y. A. Begum, M. Asaduzzaman, J.
Xicohtencatl-Cortes, E. Negrete, and M. J. Albert. 2000. Human antibody
response to longus type IV pilus and study of its prevalence among ente-
VOL. 18, 2005ETEC IN DEVELOPING COUNTRIES 481
rotoxigenic Escherichia coli in Bangladesh by using monoclonal antibodies.
J. Infect. Dis. 181:2071–2074.
134. Qadri, F., C. Wenneras, F. Ahmed, M. Asaduzzaman, D. Saha, M. J. Albert,
R. B. Sack, and A. M. Svennerholm. 2000. Safety and immunogenicity of an
oral, inactivated enterotoxigenic Escherichia coli plus cholera toxin B sub-
unit vaccine in Bangladeshi adults and children. Vaccine 18:2704–2712.
135. Quick, R. E., L. V. Venczel, O. Gonzalez, E. D. Mintz, A. K. Highsmith, A.
Espada, E. Damiani, N. H. Bean, E. H. De Hannover, and R. V. Tauxe.
1996. Narrow-mouthed water storage vessels and in situ chlorination in a
Bolivian community: a simple method to improve drinking water quality.
Am. J. Trop. Med. Hyg. 54:511–516.
136. Quiroga, M., P. Oviedo, I. Chinen, E. Pegels, E. Husulak, N. Binztein, M.
Rivas, L. Schiavoni, and M. Vergara. 2000. Asymptomatic infections by
diarrheagenic Escherichia coli in children from Misiones, Argentina, during
the first twenty months of their lives. Rev. Inst. Med. Trop. Sao Paulo
137. Rahman, M. M., S. H. Vermund, M. A. Wahed, G. J. Fuchs, A. H. Baqui,
and J. O. Alvarez. 2001. Simultaneous zinc and vitamin A supplementation
in Bangladeshi children: randomised double blind controlled trial. Br.
Med. J. 323:314–318.
138. Rao, M. C. 1985. Toxins which activate guanylate cyclase: heat-stable en-
terotoxins. Ciba Found. Symp. 112:74–93.
139. Rao, M. R., R. Abu-Elyazeed, S. J. Savarino, A. B. Naficy, T. F. Wierzba, I.
Abdel-Messih, H. Shaheen, R. W. Frenck, Jr., A. M. Svennerholm, and J. D.
Clemens. 2003. High disease burden of diarrhea due to enterotoxigenic
Escherichia coli among rural Egyptian infants and young children. J. Clin.
140. Raqib, R., S. K. Roy, M. J. Rahman, T. Azim, S. S. Ameer, J. Chisti, and J.
Andersson. 2004. Effect of zinc supplementation on immune and inflam-
matory responses in pediatric patients with shigellosis. Am. J. Clin. Nutr.
141. Ratchtrachenchai, O. A., S. Subpasu, H. Hayashi, and W. Ba-Thein. 2004.
Prevalence of childhood diarrhoea-associated Escherichia coli in Thailand.
J. Med. Microbiol. 53:237–243.
142. Regua-Mangia, A. H., T. A. Gomes, M. A. Vieira, J. R. Andrade, K. Irino,
and L. M. Teixeira. 2004. Frequency and characteristics of diarrhoeagenic
Escherichia coli strains isolated from children with and without diarrhoea in
Rio de Janeiro, Braz. J. Infect. 48:161–167.
143. Reis, M. H., B. E. Guth, T. A. Gomes, J. Murahovschi, and L. R. Trabulsi.
1982. Frequency of Escherichia coli strains producing heat-labile toxin or
heat-stable toxin or both in children with and without diarrhea in Sao
Paulo. J. Clin. Microbiol. 15:1062–1064.
144. Reis, M. H., J. C. Vasconcelos, and L. R. Trabulsi. 1980. Prevalence of
enterotoxigenic Escherichia coli in some processed raw food from animal
origin. Appl. Environ. Microbiol. 39:270–271.
145. Rosenberg, M. L., J. P. Koplan, I. K. Wachsmuth, J. G. Wells, E. J.
Gangarosa, R. L. Guerrant, and D. A. Sack. 1977. Epidemic diarrhea at
Crater Lake from enterotoxigenic Escherichia coli. A large waterborne
outbreak. Ann. Intern. Med. 86:714–718.
146. Rowland, M. G. 1986. The Gambia and Bangladesh: the seasons and diar-
rhoea. Dialogue Diarrhoea:3.
147. Rudin, A., M. M. McConnell, and A. M. Svennerholm. 1994. Monoclonal
antibodies against enterotoxigenic Escherichia coli colonization factor an-
tigen I (CFA/I) that cross-react immunologically with heterologous CFAs.
Infect. Immun. 62:4339–4346.
148. Runnels, P. L., H. W. Moon, and R. A. Schneider. 1980. Development of
resistance with host age to adhesion of K99?Escherichia coli to isolated
intestinal epithelial cells. Infect. Immun. 28:298–300.
149. Ryder, R. W., D. A. Sack, A. Z. Kapikian, J. C. McLaughlin,
J. Chakraborty, A. S. Mizanur Rahman, M. H. Merson, and J. G. Wells.
1976. Enterotoxigenic Escherichia coli and Reovirus-like agent in rural
Bangladesh. Lancet i:659–663.
150. Sack, D. A., D. C. Kaminsky, R. B. Sack, J. N. Itotia, R. R. Arthur, A. Z.
Kapikian, F. Orskov, and I. Orskov. 1978. Prophylactic doxycycline for
travelers’ diarrhea. Results of a prospective double-blind study of Peace
Corps volunteers in Kenya. N. Engl. J. Med. 298:758–763.
151. Sack, D. A., D. C. Kaminsky, R. B. Sack, I. A. Wamola, F. Orskov, I.
Orskov, R. C. Slack, R. R. Arthur, and A. Z. Kapikian. 1977. Enterotoxi-
genic Escherichia coli diarrhea of travelers: a prospective study of Ameri-
can Peace Corps volunteers. Johns Hopkins Med. J. 141:63–70.
152. Sack, D. A., J. C. McLaughlin, R. B. Sack, F. Orskov, and I. Orskov. 1977.
Enterotoxigenic Escherichia coli isolated from patients at a hospital in
Dacca. J. Infect. Dis. 135:275–280.
153. Sack, D. A., J. Shimko, O. Torres, et al. 2002. Presented at the 42nd
Interscience Conference on Antimicrobial Agents and Chemotherapy, San
154. Sack, R. B. 1968. Proceedings of the 4th Joint Conference, Japan-U.S.
Cooperative Medical Science Program, Unzen, Japan, p. 23–25.
155. Sack, R. B. 1980. Enterotoxigenic Escherichia coli: identification and char-
acterization. J. Infect. Dis. 142:279–286.
156. Sack, R. B. 1978. The epidemiology of diarrhea due to enterotoxigenic
Escherichia coli. J. Infect. Dis. 137:639–640.
157. Sack, R. B. 1975. Human diarrheal disease caused by enterotoxigenic Esch-
erichia coli. Annu. Rev. Microbiol. 29:333–353.
158. Sack, R. B. 1980. Presented at the 43rd Nobel Symp., Stockholm, Sweden.
159. Sack, R. B. 1990. Travelers’ diarrhea: microbiologic bases for prevention
and treatment. Rev. Infect. Dis. 12(Suppl. 1):S59–63.
160. Sack, R. B., J. L. Froehlich, A. W. Zulich, D. S. Hidi, A. Z. Kapikian, F.
Orskov, I. Orskov, and H. B. Greenberg. 1979. Prophylactic doxycycline for
travelers’ diarrhea: results of a prospective double-blind study of Peace
Corps volunteers in Morocco. Gastroenterology 76:1368–1373.
161. Sack, R. B., S. L. Gorbach, J. G. Banwell, B. Jacobs, B. D. Chatterjee, and
R. C. Mitra. 1971. Enterotoxigenic Escherichia coli isolated from patients
with severe cholera-like disease. J. Infect. Dis. 123:378–385.
162. Sack, R. B., N. Hirschhorn, I. Brownlee, R. A. Cash, W. E. Woodward, and
D. A. Sack. 1975. Enterotoxigenic Escherichia-coli-associated diarrheal dis-
ease in Apache children. N. Engl. J. Med. 292:1041–1045.
163. Sack, R. B., B. Jacobs, and R. Mitra. 1974. Antitoxin responses to infections
with enterotoxigenic Escherichia coli. J. Infect. Dis. 129:330–335.
164. Sack, R. B., D. A. Sack, I. J. Mehlman, F. Orskov, and I. Orskov. 1977.
Enterotoxigenic Escherichia coli isolated from food. J. Infect. Dis. 135:313–
165. Sack, R. B., A. K. Siddique, I. M. Longini, Jr., A. Nizam, M. Yunus, M. S.
Islam, J. G. Morris, Jr., A. Ali, A. Huq, G. B. Nair, F. Qadri, S. M. Faruque,
D. A. Sack, and R. R. Colwell. 2003. A 4-year study of the epidemiology of
Vibrio cholerae in four rural areas of Bangladesh. J. Infect. Dis. 187:96–
166. Samuel, S., J. Vadivelu, and N. Parasakthi. 1997. Characteristics of child-
hood diarrhea associated with enterotoxigenic Escherichia coli in Malaysia.
Southeast Asian J. Trop. Med. Public Health 28:114–119.
167. Santosham, M., R. B. Sack, R. Reid, R. Black, J. Croll, R. Yolken, L.
Aurelian, M. Wolff, E. Chan, S. Garrett, et al. 1995. Diarrhoeal diseases in
the White Mountain Apaches: epidemiologic studies. J. Diarrhoeal. Dis.
168. Sarker, S. A., M. M. Rahaman, A. Ali, S. Hossain, and A. N. Alam. 1985.
Prolonged depression of serum zinc concentrations in children following
post-measles diarrhoea. Hum. Nutr. Clin. Nutr. 39:411–417.
169. Savarino, S. J., F. M. Brown, E. Hall, S. Bassily, F. Youssef, T. Wierzba, L.
Peruski, N. A. El-Masry, M. Safwat, M. Rao, M. Jertborn, A. M. Svenner-
holm, Y. J. Lee, and J. D. Clemens. 1998. Safety and immunogenicity of an
oral, killed enterotoxigenic Escherichia coli-cholera toxin B subunit vaccine
in Egyptian adults. J. Infect. Dis. 177:796–799.
170. Savarino, S. J., E. R. Hall, S. Bassily, F. M. Brown, F. Youssef, T. F.
Wierzba, L. Peruski, N. A. El-Masry, M. Safwat, M. Rao, H. El Mohamady,
R. Abu-Elyazeed, A. Naficy, A. M. Svennerholm, M. Jertborn, Y. J. Lee, and
J. D. Clemens. 1999. Oral, inactivated, whole cell enterotoxigenic Esche-
richia coli plus cholera toxin B subunit vaccine: results of the initial eval-
uation in children. PRIDE Study Group. J. Infect. Dis. 179:107–114.
171. Savarino, S. J., E. R. Hall, S. Bassily, T. F. Wierzba, F. G. Youssef, L. F.
Peruski, Jr., R. Abu-Elyazeed, M. Rao, W. M. Francis, H. El Mohamady, M.
Safwat, A. B. Naficy, A. M. Svennerholm, M. Jertborn, Y. J. Lee, and J. D.
Clemens. 2002. Introductory evaluation of an oral, killed whole cell ente-
rotoxigenic Escherichia coli plus cholera toxin B subunit vaccine in Egyp-
tian infants. Pediatr. Infect. Dis. J. 21:322–330.
172. Schultsz, C., G. J. Pool, R. van Ketel, B. de Wever, P. Speelman, and J.
Dankert. 1994. Detection of enterotoxigenic Escherichia coli in stool sam-
ples by using nonradioactively labeled oligonucleotide DNA probes and
PCR. J. Clin. Microbiol. 32:2393–2397.
173. Scotland, S. M., R. H. Flomen, and B. Rowe. 1989. Evaluation of a reversed
passive latex agglutination test for detection of Escherichia coli heat-labile
toxin in culture supernatants. J. Clin. Microbiol. 27:339–340.
174. Sears, C. L., and J. B. Kaper. 1996. Enteric bacterial toxins: mechanisms of
action and linkage to intestinal secretion. Microbiol. Rev. 60:167–215.
175. Shaheen, H. I., K. A. Kamal, M. O. Wasfy, N. M. El-Ghorab, B. Lowe, R.
Steffen, N. Kodkani, L. Amsler, P. Waiyaki, J. C. David, S. B. Khalil, and
L. F. Peruski, Jr. 2003. Phenotypic diversity of enterotoxigenic Escherichia
coli (ETEC) isolated from cases of travelers’ diarrhea in Kenya. Int. J. In-
fect. Dis. 7:35–38.
176. Sharp, T. W., S. A. Thornton, M. R. Wallace, R. F. Defraites, J. L. Sanchez,
R. A. Batchelor, P. J. Rozmajzl, R. K. Hanson, P. Echeverria, A. Z.
Kapikian, et al. 1995. Diarrheal disease among military personnel during
Operation Restore Hope, Somalia, 1992–1993. Am. J. Trop. Med. Hyg.
177. Smith, H. W., and S. Halls. 1967. Observations by the ligated intestinal
segment and oral inoculation methods on Escherichia coli infections in pigs,
calves, lambs and rabbits. J. Pathol. Bacteriol. 93:499–529.
178. Smith, H. W., and M. A. Linggood. 1971. The transmissible nature of
enterotoxin production in a human enteropathogenic strain of Escherichia
coli. J. Med. Microbiol. 4:301–305.
179. So, M., W. S. Dallas, and S. Falkow. 1978. Characterization of an Esche-
richia coli plasmid encoding for synthesis of heat-labile toxin: molecular
cloning of the toxin determinant. Infect. Immun. 21:405–411.
180. Sommerfelt, H., H. Steinsland, H. M. Grewal, G. I. Viboud, N. Bhandari,
W. Gaastra, A. M. Svennerholm, and M. K. Bhan. 1996. Colonization
482QADRI ET AL.CLIN. MICROBIOL. REV.
factors of enterotoxigenic Escherichia coli isolated from children in north
India. J. Infect. Dis. 174:768–776.
181. Stacy-Phipps, S., J. J. Mecca, and J. B. Weiss. 1995. Multiplex PCR assay
and simple preparation method for stool specimens detect enterotoxigenic
Escherichia coli DNA during course of infection. J. Clin. Microbiol. 33:
182. Steinsland, H., P. Valentiner-Branth, H. M. Grewal, W. Gaastra, K. K.
Molbak, and H. Sommerfelt. 2003. Development and evaluation of geno-
typic assays for the detection and characterization of enterotoxigenic Esch-
erichia coli. Diagn. Microbiol. Infect. Dis. 45:97–105.
183. Steinsland, H., P. Valentiner-Branth, M. Perch, F. Dias, T. K. Fischer, P.
Aaby, K. Molbak, and H. Sommerfelt. 2002. Enterotoxigenic Escherichia
coli infections and diarrhea in a cohort of young children in Guinea-Bissau.
J. Infect. Dis. 186:1740–1747.
184. Stintzing, G., R. Mollby, and D. Habte. 1982. Enterotoxigenic Escherichia
coli and other enteropathogens in paediatric diarrhoea in Addis Ababa.
Acta Paediatr. Scand. 71:279–286.
185. Stoll, B. J., R. I. Glass, M. I. Huq, M. U. Khan, J. E. Holt, and H. Banu.
1982. Surveillance of patients attending a diarrhoeal disease hospital in
Bangladesh. Br. Med. J. (Clin. Res. Ed.) 285:1185–1188.
186. Stoll, B. J., B. Rowe, R. I. Glass, R. J. Gross, and I. Huq. 1983. Changes in
serotypes of enterotoxigenic Escherichia coli in Dhaka over time: usefulness
of polyvalent antisera. J. Clin. Microbiol. 18:935–937.
187. Stoll, B. J., A. M. Svennerholm, L. Gothefors, D. Barua, S. Huda, and J.
Holmgren. 1986. Local and systemic antibody responses to naturally ac-
quired enterotoxigenic Escherichia coli diarrhea in an endemic area. J. In-
fect. Dis. 153:527–534.
188. Subekti, D. S., M. Lesmana, P. Tjaniadi, N. Machpud, Sriwati, Sukarma,
J. C. Daniel, W. K. Alexander, J. R. Campbell, A. L. Corwin, H. J. Beecham,
3rd, C. Simanjuntak, and B. A. Oyofo. 2003. Prevalence of enterotoxigenic
Escherichia coli (ETEC) in hospitalized acute diarrhea patients in Den-
pasar, Bali, Indonesia. Diagn. Microbiol. Infect. Dis. 47:399–405.
189. Svennerholm, A. M., C. Ahren, and M. Jertborn. 1997. Oral inactivated
vaccines against enterotoxigenic Escherichia coli, ed. II. Marcel Dekker Inc,
New York, NY.
190. Svennerholm, A. M., and J. Holmgren. 1978. Identification of Escherichia
coli heat-labile enterotoxin by means of a ganglioside immunosorbent assay
(GM1-ELISA) procedure. Curr. Microbiol. 1:19–23.
191. Svennerholm, A. M., and J. Holmgren. 1995. Oral vaccines against cholera
and enterotoxigenic Escherichia coli diarrhea. Adv. Exp. Med. Biol. 371B:
192. Svennerholm, A. M., J. Holmgren, and D. A. Sack. 1989. Development of
oral vaccines against enterotoxinogenic Escherichia coli diarrhoea. Vaccine
193. Svennerholm, A. M., and S. J. Savarino. 2004. Oral inactivated whole cell
B subunit combination vaccine against enterotoxigenic Escherichia coli.,
3rd ed. Marcel Decker, New York, NY.
194. Svennerholm, A. M., and D. Steele. 2004. Progress in enteric vaccine de-
velopment. Best Practice Res. Clin. Gastroentrol. 18:421–445.
195. Svennerholm, A. M., C. Wenneras, J. Holmgren, M. M. McConnell, and B.
Rowe. 1990. Roles of different coli surface antigens of colonization factor
antigen II in colonization by and protective immunogenicity of enterotoxi-
genic Escherichia coli in rabbits. Infect. Immun. 58:341–346.
196. Svennerholm, A. M., and G. Wiklund. 1983. Rapid GM1-enzyme-linked
immunosorbent assay with visual reading for identification of Escherichia
coli heat-labile enterotoxin. J. Clin. Microbiol. 17:596–600.
197. Svennerholm, A. M., M. Wikstrom, M. Lindblad, and J. Holmgren. 1986.
Monoclonal antibodies against Escherichia coli heat-stable toxin (STa) and
their use in a diagnostic ST ganglioside GM1-enzyme-linked immunosor-
bent assay. J. Clin. Microbiol. 24:585–590.
198. Tacket, C. O., G. Losonsky, S. Livio, R. Edelman, J. Crabb, and D. Freed-
man. 1999. Lack of prophylactic efficacy of an enteric-coated bovine hyper-
immune milk product against enterotoxigenic Escherichia coli challenge
administered during a standard meal. J. Infect. Dis. 180:2056–2059.
199. Taylor, J., M. P. Wilkins, and J. M. Payne. 1961. Relation of rabbit gut
reaction to enteropathogenic Escherichia coli. Br. J. Exp. Pathol. 42:43–52.
200. Toma, C., Y. Lu, N. Higa, N. Nakasone, I. Chinen, A. Baschkier, M. Rivas,
and M. Iwanaga. 2003. Multiplex PCR assay for identification of human
diarrheagenic Escherichia coli. J. Clin. Microbiol. 41:2669–2671.
201. Torres, O. 2003. Presented at the meeting on enterotoxigens in Montreux,
202. Tsen, H. Y., L. Z. Jian, and W. R. Chi. 1998. Use of a multiplex PCR system
for the simultaneous detection of heat labile toxin I and heat stable toxin II
genes of enterotoxigenic Escherichia coil in skim milk and porcine stool. J.
Food Prot. 61:141–145.
203. Turner, A. K., T. D. Terry, D. A. Sack, P. Londono-Arcila, and M. J.
Darsley. 2001. Construction and characterization of genetically defined aro
omp mutants of enterotoxigenic Escherichia coli and preliminary studies of
safety and immunogenicity in humans. Infect. Immun. 69:4969–4979.
204. Valvatne, H., H. Steinsland, and H. Sommerfelt. 2002. Clonal clustering
and colonization factors among thermolabile and porcine thermostable
enterotoxin-producing Escherichia coli. APMIS 110:665–672.
205. VanDerslice, J., B. Popkin, and J. Briscoe. 1994. Drinking-water quality,
sanitation, and breast-feeding: their interactive effects on infant health.
Bull. W.H.O. 72:589–601.
206. Viboud, G. I., N. Binsztein, and A. M. Svennerholm. 1993. Characterization
of monoclonal antibodies against putative colonization factors of entero-
toxigenic Escherichia coli and their use in an epidemiological study. J. Clin.
207. Viboud, G. I., M. J. Jouve, N. Binsztein, M. Vergara, M. Rivas, M. Quiroga,
and A. M. Svennerholm. 1999. Prospective cohort study of enterotoxigenic
Escherichia coli infections in Argentinean children. J. Clin. Microbiol. 37:
208. Vidal, R., M. Vidal, R. Lagos, M. Levine, and V. Prado. 2004. Multiplex
PCR for diagnosis of enteric infections associated with diarrheagenic Esch-
erichia coli. J. Clin. Microbiol. 42:1787–1789.
209. Weiner, M., and J. Osek. 2004. Development of a multiplex PCR (m-PCR)
test for rapid identification of genes encoding heat-labile (LTI) and heat-
stable (STI and STII) toxins of enterotoxigenic Escherichia coli (ETEC)
with internal control of amplification. Acta Microbiol. Pol. 53:7–10.
210. Wiedermann, G., H. Kollaritsch, M. Kundi, A. M. Svennerholm, and U.
Bjare. 2000. Double-blind, randomized, placebo controlled pilot study eval-
uating efficacy and reactogenicity of an oral ETEC B-subunit-inactivated
whole cell vaccine against travelers’ diarrhea (preliminary report). J. Travel
211. Wolf, M. K. 1997. Occurrence, distribution, and associations of O and H
serogroups, colonization factor antigens, and toxins of enterotoxigenic
Escherichia coli. Clin. Microbiol. Rev. 10:569–584.
212. Wolf, M. K., D. N. Taylor, E. C. Boedeker, K. C. Hyams, D. R. Maneval,
M. M. Levine, K. Tamura, R. A. Wilson, and P. Echeverria. 1993. Charac-
terization of enterotoxigenic Escherichia coli isolated from U.S. troops
deployed to the Middle East. J. Clin. Microbiol. 31:851–856.
213. Wood, L. V., W. H. Wolfe, G. Ruiz-Palacios, W. S. Foshee, L. I. Corman, F.
McCleskey, J. A. Wright, and H. L. DuPont. 1983. An outbreak of gastro-
enteritis due to a heat-labile enterotoxin-producing strain of Escherichia
coli. Infect. Immun. 41:931–934.
214. World Health Organization. 1999. New frontiers in the development of
vaccines against enterotoxigenic (ETEC) and enterohaemorrhagic (EHEC)
E. coli infections. Weekly Epidemiol. Rec. 13:98–100.
215. World Health Organization. 2004. Report of the Meeting on Future Di-
rections for Research on ETEC Vaccines for Developing Countries. World
Health Organization, Geneva, Switzerland.
216. World Health Organization. 1989. The treatment and prevention of acute
diarrhea, practical guidelines, 2nd ed. World Health Organization, Geneva,
217. Yolken, R. H., H. B. Greenberg, M. H. Merson, R. B. Sack, and A. Z.
Kapikian. 1977. Enzyme-linked immunosorbent assay for detection of
Escherichia coli heat-labile enterotoxin. J. Clin. Microbiol. 6:439–444.
VOL. 18, 2005 ETEC IN DEVELOPING COUNTRIES 483