Household Transmission of STEC O157 • CID 2008:46 (15 April) • 1189
M A J O R A R T I C L E
Preventing Household Transmission of Shiga Toxin–
Producing Escherichia coli O157 Infection: Promptly
Separating Siblings Might Be the Key
Dirk Werber,1,2Brendan W. Mason,1Meirion R. Evans,1and Roland L. Salmon1
1Communicable Disease Surveillance Centre, National Public Health Service for Wales, Temple of Peace and Health, Cathays Park, Cardiff,
United Kingdom, and
2European Programme for Intervention Epidemiology Training
(See the editorial commentary by Ahn et al. on pages 1197–9)
Preventing household transmission of Shiga toxin–producing Escherichia coli O157 (STEC O157)
infection is important because of the ease of interpersonal transmission and the potential disease severity.
We conducted a retrospective cohort study of households associated with an outbreak of STEC O157
infection in South Wales, United Kingdom, in autumn 2005. We investigated whether characteristics of the primary
case patient or the household were predictors for secondary household transmission of STEC O157 infection.
Furthermore, we estimated the proportion of cases that might be prevented by isolation (e.g., hospitalization) of
the primary case patient immediately after the microbiological diagnosis and the number of patients with STEC
O157 who would need to be isolated to prevent 1 case of hemolytic uremic syndrome. Based on dates of symptom
onset, case patients in households were classified as having primary, coprimary, or secondary infection. Secondary
cases were considered to be preventable if the secondary case patient’s symptoms started 11 incubation period (4
days) after the date of microbiological diagnosis of the primary case.
Eighty-nine (91%) of 98 eligible households were enrolled. Among 20 households (22%), 25secondary
cases were ascertained. Thirteen secondary cases (56%) occurred in siblings of the primary case patients;hemolytic
uremic syndrome developed in 4 of these siblings. Presence of a sibling (risk ratio, 3.8; 95% confidence interval,
0.99–14.6) and young age (!5 years) of the primary case patient (risk ratio, 2.03; 95% confidence interval, 0.99–
41.6) were independent predictors for households in which secondary cases occurred. Of the 15 secondary cases
for which complete information was available, 7 (46%) might have been prevented. When restricting isolation to
primary case patients who were aged !10 years and who had a sibling, we estimated the number of patients who
would need to be isolated to prevent 1 case of hemolytic uremic syndrome to be 47 patients (95% confidence
interval, 16–78 patients).
Promptly separating pediatric patients with STEC O157 infectionfromtheiryoungsiblingsshould
On Friday 16 September 2005, the National Public
Health Service for Wales was notified of the first cases
of bloody diarrhea in what became the second-largest
outbreak of Shiga toxin–producing Escherichia coli
(STEC) O157 infection in the United Kingdom .
Received 8 October 2007; accepted 3 January 2008; electronically published
18 March 2008.
Reprints or correspondence: Dr. Dirk Werber, Robert Koch-Institute, Dept. for
Infectious Disease Epidemiology, Seestraße 10, 13353 Berlin, Germany
Clinical Infectious Diseases2008;46:1189–96
? 2008 by the Infectious Diseases Society of America. All rights reserved.
Eventually, there were 157 cases that met the clinical
case definition, 118 of which were microbiologically
confirmed. Primary cases mostly involvedchildrenwho
attended 44 schools (mainly elementary schools) in 4
local authorities. Thirty-one patients were hospitalized,
11 of whom developed hemolytic uremia syndrome
(HUS), and tragically, one 5-year-old child died. The
vehicle of infection was delicatessen meat produced by
a single supplier that was served in school meals
The National Assembly for Wales set up the E. coli
Public Inquiry to undertake a thorough investigation
into the outbreak under The Inquiries Act 2005. The
Act enables a public inquiry to be held when events
have caused or are capable of causing public concern
or if there is public concern that particular events may
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1190 • CID 2008:46 (15 April) • Werber et al.
have occurred. The Inquiry’s terms of reference are “[to] in-
quire into the circumstances that led to the outbreak of E. coli
O157 infection in South Wales in September 2005, and into
the handling of the outbreak; and to consider the implications
for the future and make recommendations accordingly” .
The Inquiry has legal power to call witnesses and to compel
witnesses to give evidence, either in writing or orally, and to
produce any relevant documents.
The Outbreak Control Team had identified the vehicle of
infection by Sunday 18 September. The Inquiry has stated that
the Team “succeeded in identifying a common link between
the cases at a very early stage. They reacted with commendable
speed and applied a precautionary and very wise approach that
led to early steps being taken to remove cooked meat from the
food chain” . However, despite the rapid removal of the
primary source of infection, secondary transmission occurred.
This article investigates the potential of isolating pediatric pa-
tients with STEC O157 infection to prevent secondary house-
STEC O157 infection can cause life-threateningHUS,especially
in children. Secondary infection due to STEC O157, compared
with secondary infection due to most other bacterial enteric
pathogens, through person-to-person transmission is common
 and well documented in various settings (e.g., child day
care facilities [5, 6], nursing homes , and households ).
Considering both the ease of interpersonal transmission and
the potential disease severity, preventing secondary transmis-
sion of this pathogen presents a difficult but important chal-
lenge for infection control. Importantly, even for large food-
borne outbreaks of STEC O157 infection, it has been estimated
that a modestly effective strategy to interrupt secondary trans-
mission could result in a reduction of 5%–11% of symptomatic
cases of STEC O157 infection .
In most countries, including the United States, pediatric pa-
tients with STEC O157 infection are excluded from school or
nursery and, unless hospitalized, usually are cared for at home.
To prevent secondary household spread, personsprovidingcare
are suitably advised about appropriate enteric precautions,
particularly the necessity for thorough andfrequenthandwash-
ing with soap . The effectiveness of measures, such as
prompt isolation of the primary case patient (e.g., by hospi-
talization ), for preventing household transmission has not
yet been investigated. Analyzing the characteristics of house-
holds where secondary transmission has occurred may allow
for a more targeted infection-control policy.
In autumn 2005, a large foodborne outbreak of infection
due to STEC O157:H7 (hereafter referred to as STEC O157)
occurred in South Wales, United Kingdom, predominantly af-
fecting school-aged children in 46 different schools . Sub-
typing of isolates by PFGE suggested that all cases comprised
a single outbreak group. More than 1 case occurred in several
households, and secondary transmission of infection among
household members was frequently suspected. The objectives
of this study were 2 fold. First, we sought to investigatewhether
characteristics of the primary case patient or the household
structure were predictors for households where secondarycases
had occurred. Second, we estimated the proportion of cases
that might be prevented by isolation of the primary casepatient
immediately after microbiological diagnosis and the number of
patients who would need to be isolated (NNI) to prevent 1
case of HUS, to assess the potential effectiveness of this inter-
vention for the prevention and control of STEC O157infection.
MATERIAL AND METHODS
Study design and definitions.
cohort study including non–single-person households inwhich
at least 1 outbreak case of STEC O157 infection occurred from
15 September through 1 November 2005 in the 3 most affected
local authority areas in South Wales (i.e., Caerphilly, Merthyr
Tydfil, and Rhonda-Cynon-Taf). Information from records on
patients and their contacts, collected as part of the outbreak
investigation, was collated through personal interviews with
environmental health officers in December 2005.
A case patient was defined as any person residing in the
study area and presenting with eitheraculture-confirmedSTEC
O157 infection or bloody diarrhea from September through
October 2005 (the working definition for case patients during
the outbreak investigation). A primary case patient was defined
as the person with the earliest date of onset of symptoms in
the household. A household was any residence where a primary
case patient stayed for at least 1 day from the date of onset of
symptoms to the date when a stool specimen last testedpositive
for STEC O157. A household contact was any person who
stayed in the same household as a primary case patient for at
least 1 night or who had, in the judgment of the environmental
health officer, close contact with the primary case patient in
the household environment during the infectious period.Other
case patients in the household were categorized as having co-
primary or secondary infection, depending on the interval be-
tween the date of onset of their symptoms and the date of onset
of symptoms in the primary case patient. Because the median
incubation period for STEC O157 infection has been estimated
to be 3–4 days [14–16], we assumed that the incubation period
for all cases in this outbreak was 4 days. Thus, household con-
tacts whose symptoms started within 4 days after symptom
onset in the primary case patient were classified as having co-
primary infection (coprimary case patients), and those whose
symptoms started ?5 days after symptom onset in the primary
case patient were classified as having secondary infection (sec-
ondary case patients). Asymptomatic excreters, who received
We conducted a retrospective
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Household Transmission of STEC O157 • CID 2008:46 (15 April) • 1191
of cases in household contacts in a large outbreak of Shiga toxin–producing Escherichia coli (STEC) O157
infection in South Wales, United Kingdom, 2005.
Classification of households according to characteristics of primary case patientsand occurrence
Characteristic of the primary case patient
in which a
No. of households in
which a secondary
case did not occur
Symptomatic, culture-confirmed STEC O157 infection
Bloody diarrhea; no evidence of STEC O157 infection
Asymptomatic, culture-confirmed STEC O157 infection
Shiga toxin–producing Escherichia coli O157 infection in South Wales, United Kingdom,
2005, by family relation to the primary case patient.
Secondary attack rates among household contacts in a large outbreak of
Relationship of the secondary case patient
to the primary case patient
No. of secondary
no. of household contactsAttack rate, %
Other close contactsa
aIncluded other family members, friends, neighbors, and other contacts.
Secondary cases included asymptomatic cases thatoccurredingrandparents(
), and a sibling ( ).np 1
diagnoses by screening of household contacts, were also con-
sidered to be secondary case patients if their infections were
identified within 1 month after symptom onset in primary case
patients who attended outbreak-associated schools. Because of
the possibility of transmission within a school, we excluded
households if the secondarycasepatientattendedaschoolother
than the school attended by the primary case patient but that
was also considered to be a site of the outbreak.
The unitof analysiswasthehousehold,
and the primary outcome measure was a secondary case oc-
curring in the household. We examined 8 risk factors. The 5
following variables related to the primary case patient: age, sex,
presence of culture-confirmed infection with symptoms, hos-
pitalization, and development of HUS (HUS was diagnosed
clinically by pediatric nephrologists in patients with acuteonset
of microangiopathic hemolytic anemia,thrombocytopenia,and
renal injury). The other 3 following variables related to house-
hold contacts: presence of a sibling, total number of household
contacts, and number of household contacts living at the main
residence of the primary case patient (defined as the residence
where the primary case patient spent most nights of the week).
Secondary attack rates among all household contacts and
among subgroups of these contacts (e.g., siblings) were cal-
culated. We computed the proportion of households where a
secondary case occurred among exposed and unexposedhouse-
holds for all dichotomous exposures and divided the 2 attack
rates to obtain unadjusted risk ratios (RRs) with 95% CIs. For
continuous variables, median values were calculated for house-
holds in which a secondary case occurred and households in
which a secondary case did not occur. Bivariable significance
testing was performed using Fisher’s exact test for dichotomous
variables and the Wilcoxon rank sum test for continuous var-
iables. Stata, release 9.0 (Stata), was used for statistical analysis.
A multivariable Poisson regression model with robust error
variance was used  to obtain adjusted RRs for the age of
the primary case patient and the presence of a sibling in the
household. To examine the effect of other variables, we added
them in a stepwise fashion according to their P value in bi-
variable analysis. Variables were retained in the multivariable
model if their P value was !.1. We included age as a binary
variable andselectedacutoff (age,5years)basedonthefindings
of a previous study of household transmission of STEC O157
infection . Using the variables retained in the final model,
we classified households as being at risk for having secondary
cases in the household and calculated the sensitivity and the
positive predictive value (PPV) of this categorization. This al-
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1192 • CID 2008:46 (15 April) • Werber et al.
coli O157 infection in South Wales, United Kingdom, 2005. HUS, hemolytic uremic syndrome.
Number of days between symptom onset in primary and secondary case patients in a large outbreak of Shiga toxin–producingEscherichia
lowed us to retrospectively assess how accurately households
in which secondary cases occurred could have been identified.
We also estimated the proportion of symptomatic cases that
potentially could have been prevented by isolating all primary
case patients immediately after these patients received their
microbiological diagnosis. This was done by calculating the
proportion of secondary cases patients who experienced the
onset of symptoms ?5 days after corresponding patients re-
ceived their microbiological diagnosis. We used this number as
the estimate of the absoluterisk reduction(ARR)amonghouse-
holds in which secondary cases occurred, had such an inter-
vention been applied.
To estimate the NNI to prevent 1 case of HUS, we modified
the standard calculation for the “number needed to treat”mea-
sure (1/ARR) [18, 19] by multiplying the ARR by the propor-
tion of households in which secondary cases occurred (Psecondary
cases). This approach took into account the fact that somehouse-
holds where the intervention would be applied were not at risk
(i.e., households in which a secondary case did not occur). We
then multiplied this estimate by a factor of 10 on the basis of
the assumption that the risk of patients with STEC O157 in-
fection developing HUS, which is strongly age dependent, is
estimated to be ∼10% [20–22],
Because it is probably impractical to strictly isolate all primary
case patients, we also calculated this measure for primary case
patients from at-risk households only (NNIHHatrisk). To perform
this calculation, we used the same formula but replaced the
proportion of households in which secondary cases occurred
with the PPV for classifying households as being at risk for
having secondary cases.
HH at risk
We calculated 95% CIs for the NNI measure, assuming that
the estimated proportions were independent and following a
binomial distribution, taking into account the Gaussian prop-
agation of errors of single estimates contained in the formulas.
in which at least 1 case occurred. Households were excluded,
because a nonprimary case patient attended a school that was
associated with the outbreak (n p 5
complete ( ), and the household was a single-personn p 3
household ( ). At least 1 secondary case occurred in 20n p 1
households (22%) (table 1). Altogether, 469 householdcontacts
were ascertained, 107 of whom were siblings (median number
of contacts per household, 5; range, 1–19); 278 (59%) were
household contacts living in the main residence of the primary
The median age of the 89 primary case patients was 7 years
(range, 1–59 years), and 75% were !10 years of age. In 11
households, the primary case patient was an adult. No sec-
ondary case was observed in contacts of these households.Also,
fewer contacts lived in these households, comparedwithhouse-
holds in which the primary case patient was not an adult (me-
dian number of contacts, 3 vs. 5;
case patients, 56 (63%) had both gastroenteritis and a culture-
confirmed STEC infection (table 1).
There were 25 secondary case patients (secondaryattackrate,
5%) living in 20 households; 24 of these patients had culture-
confirmed STEC O157 infection. The median difference in
dates of symptom onset between case patients with primary
and secondary infection was 9 days (range, 5–26 days) (figure
1). In 18 (90%) of 20 households in which a secondary case
occurred, the primary case patient had symptomatic, culture-
confirmed STEC O157 infection (table 1). Fourteen secondary
case patients (56%) were female, and 5 were asymptomatic;the
median age of these patients was 7 years (range, 1–71 years).
All 25 secondary cases occurred infamilymembers,22ofwhom
lived at the same residence as the primary case patients (sec-
ondary attack rate, 8%) and 3 of whom (all adult caregivers)
), the information was in-
). Of the 89 primaryP p .012
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Household Transmission of STEC O157 • CID 2008:46 (15 April) • 1193
lived at a different residence (secondary attack rate, 2%). Four-
teen secondary case patients (56%) were siblings of the primary
case patient (median age, 3 years; range, 1–8 years), and 6 were
mothers (table 2). HUS developed in 4 of the 107 siblings
(secondary attack rate for HUS among siblings, 3.7%; 95% CI,
1.0%–9.3%). In 18 (90%) of the households in which a sec-
ondary case occurred, a sibling of the primary case patientlived
in the household (table 3).
Risk factor analysis.
Primary case patients who stayed in
households in which secondary cases occurred were signifi-
cantly younger (median age, 5 years; range, 1–10 years) than
such patients who stayed in households in which a secondary
case did not occur (median age, 8 years; range, 2–59 years;
) (table 3). A higher number of household contacts
P ! .001
who lived in the main residence with the primary case patient
stayed in households in which secondary cases occurred than
stayed in households in which a secondary case did not occur
(median number of such contacts, 4 vs. 3;
dichotomous risk factors, all of the households in which the
primary case patient was male, was aged !5 years, had a sibling,
or had symptomatic culture-confirmed STEC O157 infection
had a higher risk of having a secondary case in the household
In the final regression model, secondary cases were more
likely to occur in households in which the primary case patient
had a sibling (RR, 3.81) and the primary case patient was aged
!5 years (RR, 2.03) (table 3). The strongest point estimate of
effect was for households in which the primary case patients
had symptomatic, culture-confirmed STEC O157 infections
Potentially preventable cases and NNI.
mation was available for 15 of the 25 secondary case patients
(for 5 patients, there was no date of symptom onset, because
they were asymptomatic, and for 5 more patients,thedatewhen
the primary case patient received the microbiological diagnosis
was unknown). Seven (46%) of the 15 secondary cases were
considered to be preventable. This equates to an estimatedARR
of 0.5 (95% CI, 0.2–0.7) for immediate isolation of all primary
case patients. Of the 89 households, 35 (39%) were retrospec-
tively classified as at risk for having a secondary case (table 4).
Among these households were 16 (80%) of the 20 households
with secondary case patients, including all 4 households with
secondary case patients with HUS.
The NNI to prevent 1 case of HUS was estimated to be 95
(95% CI, 38–200). If the isolation policy was restricted to pri-
mary case patients in at-risk households only, 47 (95% CI, 16–
78) primary case patients aged !10 years would need to be
isolated to prevent 1 case of HUS. Furthermore,isolationwould
be required in only 39% of all households, although 4 (20%)
of the 20 households in which secondary cases occurred would
be missed because they were incorrectly classified as not being
P p .02
at risk. These households included the only 2 in which the
primary case patient did not have his or her infection micro-
case patients were adult caregivers of a primary case patient
who lived at another residence.
In this cohort study, basic information about primary case
patients and their households was predictive of households
where secondary cases of STEC O157 infection occurred.
Household transmission occurred mostly from children (aged
!10 years) with culture-confirmed infection to their young sib-
lings. Young age of the primary case patient (!5 years) and the
presence of a sibling independently increased the risk of house-
holds having secondary cases. Isolation of all symptomatic pri-
mary patients immediately after they receive microbiological
diagnoses of STEC O157 infection could potentially decrease
the number of secondary household cases by 50%. By focusing
on households where the primary case patient is aged !10 years
and has a sibling, we estimated the NNI to prevent 1 case of
HUS to be 47 patients (95% CI, 16–78 patients). This suggests
a large preventive potential for this intervention.
Our results are in concordance with a previous study of
sporadic STEC O157 infection in Wales , in which young
age of the primary case patient (!5 years) and of the household
contact conferred the greatest risk of transmittingandacquiring
STEC O157 infection, respectively. Young age has also been
documented as a risk factor for secondary spread in a study
of household transmission of gastroenteritis, irrespective of the
infectious agent . The secondary attack rate in our study
(5% among all household contacts and 8% among contacts
living in the main household of the primary case patient) is
similar to that found in the study of sporadic STEC O157
infection in Wales (4%–15%)  and in the study of all-cause
gastroenteritis (9%) . However, some caution must be ex-
ercised when comparing secondary attack rates among studies,
because these rates largely depend on the definitions of cases,
households, and household contacts.
Diarrheal illness in a family member is a risk factor for
developing HUS [24, 25]. A Canadian study estimated that
contact with a household member with diarrhea accounted for
150% of pediatric HUS study cases ,underpinningtheneed
for an appropriate prevention measure. To prevent the house-
hold transmission of STEC O157 and, probably, of other path-
ogens causing gastroenteritis, a key strategy appears to be the
prompt separation of primary patients from their sibling(s) or
other young household members. For instance, either the pri-
mary patient or the vulnerable sibling(s) could be temporarily
cared for by relatives or friends, as suitably advised. Alterna-
tively, primary case patients could be isolated in a hospital,
although in a large outbreak, such as this one, not enough
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1194 • CID 2008:46 (15 April) • Werber et al.
coli O157 infection in South Wales, United Kingdom, 2005.
Risk factors for households having a secondary case patient in a large outbreak of Shiga toxin–producing Escherichia
risk ratio (95% CI)
No. of households
total no. of
households Attack rate, %
No. of households
total no. of
households Attack rate, % Risk ratio (95% CI)P
Age !5 years
Had a sibling living in
1/425 19/8423 1.10 (0.19–6.32)…
18/56 32 2/3306 5.30 (1.31–21.42) 5.00 (1.24–20.14).023
transmission in a large outbreak of Shiga toxin–producing Escherichia coli O157 infection in South Wales, United
Kingdom, 2005, based on variables retained in a multivariable risk factor model.
Positive predictive value (PPV) and sensitivity for classifying households as at risk for secondary
Age of the
case patient, years
At-risk household Household not at risk
In which a
In which a
did not occur
In which a
In which a
did not occur
symptoms and a sibling. PPV was defined as the proportion of at-risk households in which secondary cases occurred. Sensitivity was
defined as the proportion of households in which secondary cases occurred that were correctly classified as being at risk.
At-risk households were defined as households where the primary case patient with the culture-confirmed infection had
single rooms may be available. Hospitalization of pediatric pri-
mary patients would have severaladvantages.First,asubstantial
proportion of patients will be hospitalized anyway (20% in this
outbreak), some of whom will develop HUS, and in these in-
stances, will be hospitalized sooner. Second, hospitalization
should achieve the largest risk reduction, because the source is
removed from the community, infection control is performed
by professionals rather than by lay caregivers, and the patients
are usually hospitalized in single rooms. Third, early intrave-
nous volume expansion—requiring expeditious hospitaliza-
tion—might mitigate the risk of patients developingsevere(oli-
goanuric) forms of HUS . An informed decision about case
management should consider the family and household struc-
ture, timeliness of microbiological diagnosis, and abilityorwill-
ingness of caregivers to adhere to advice regarding hygiene.
One-half of the secondary case patients became ill during
the first 8 days after symptom onset in the primary casepatient.
Thus, household transmission frequently occurred early during
the course of disease. Because time is of the essence, rapid
microbiological diagnosis of STEC O157 infection is vital for
pediatric patients with young siblings living in the same house-
hold. In addition, vascular injury leading to HUS could already
be under way by the time that STEC-infected patients seek
medical care . It has, therefore, been suggested that hos-
pitalization be considered on clinical grounds, even before mi-
crobiological diagnosis is made for patients with acute bloody
diarrhea, particularly if no fever is documented in a medical
setting and for those with very painful diarrhea . In this
study, the median interval between symptom onset and culture
confirmation was 5.5 days, and therefore, we believe that, at
least in outbreaks of STEC O157 infection, prompt hospitali-
zation on clinical grounds (i.e., without waiting for micribiol-
ogical confirmation of STEC O157 infection) should be seri-
ously considered. Otherwise, crucial time may already have
elapsed by the time that the microbiological diagnosis is
Risk for secondary transmission was much higher in house-
holds in which the primary case patient was symptomatic and
had a culture-confirmed STEC O157 infection than in those
in which the primary case patient had either no symptoms or
unconfirmed infection. Conversely, household transmission
was seldom observed when the primary case patient did not
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Household Transmission of STEC O157 • CID 2008:46 (15 April) • 1195
have a culture-confirmed infection. It is possible that some of
these primary case patients were misclassified and did not ac-
tually have STEC O157 infection. Alternatively, there may have
been few organisms present in stool specimens from these pa-
tients. Thus, infection may have gone unrecognized by the
conventional culture-based detection methods used in this out-
break, which are less sensitive than those based on detecting
Shiga toxin genes by PCR . It would also be a plausible
explanation for why the risk for secondary spread was lower
in these households.
This study has a number of limitations, mainly related to
some of the underlying assumptions. For example, we assumed
that household transmission always resulted from person-to-
person transmission, although there is evidence that household
transmission may also occur through contaminated objects
(e.g., through towel sharing ). Therefore, isolation of pe-
diatric patients with STEC O157 infection should always be
accompanied by other enteric precautions in the household,
such as separate washing of bed linen, towels, and soiled cloth-
ing and appropriate cleaning of toilet seats and flush handles
. Furthermore, a few secondary case patients may have
acquired infection outside the household (e.g., in school). The
assumption that the incubation period for all cases was 4 days,
although in line with published data on incubation periods,
may have led to some misclassification of household contact
cases. When performing sensitivity analysis on the data set,
assuming incubation periods of 3 days and 7 days, we obtained
a similar strength of association for the identified risk factors
(data not shown). Finally, we were not able to obtain more-
detailed exposure information about households that might
have allowed us to more precisely characterize the circum-
stances in which secondary transmission had occurred. How-
ever, clinicians in general practice are already flooded with
guidelines , and therefore, it is debatable whether using a
more accurate but more complex characterization of at-risk
households would help in formulating practical and easy-to-
remember prevention guidelines.
The secondary attack rate for HUS among siblings in this
outbreak of STEC O157 infection was 4%, indicating that a
case of STEC O157 infection in a child should be considered
to be a medicalemergency.Bycomparison,thesecondaryattack
rate is estimated to be 10 times lower for meningococcaldisease
. As a corollary, the number of household contacts needed
to be treated with chemoprophylaxis to prevent 1 secondary
household case of meningococcal disease is estimated to be 218
persons . This is considerably more than the number of
patients with STEC O157 infection that we estimated would
need to be isolated to prevent 1 case of HUS, even allowing
for failures in isolating the patients. Therefore, we conclude
that prompt separation of pediatric patients with STEC O157
infection from their young siblings should be considered.
We thank our National Public Health Service colleagues; the environ-
mental health officers in Caerphilly, Merthyr Tydfil, and Rhonda-Cynon-
Taf County Borough Councils; laboratory staff and other members of the
Outbreak Control Team, for their willingness and determination in sup-
porting this study; and GuangYong Zou and Matthias an der Heiden, for
Potential conflicts of interest.
All authors: no conflicts.
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