An outbreak of Cryptosporidium hominis infection at an
Illinois recreational waterpark
L. M. CAUSER1,2*, T. HANDZEL1,2, P. WELCH3, M. CARR4, D. CULP4, R. LUCHT4,
K. MUDAHAR4, D. ROBINSON4, E. NEAVEAR3, S. FENTON3, C. ROSE3,
L. CRAIG3, M. ARROWOOD1, S. WAHLQUIST1, L. XIAO1, Y.-M. LEE1, L. MIREL1,
D. LEVY1, M. J. BEACH1, G. POQUETTE3AND M. S. DWORKIN5
1Division of Parasitic Diseases, National Center of Infectious Diseases, Centers for Disease Control and
Prevention, Atlanta, GA, USA
2Epidemic Intelligence Service, Division of Applied Public Health Training, Epidemiology Program Office,
Centers for Disease Control and Prevention, Atlanta, GA, USA
3Tazewell County Health Department, Tremont, IL, USA
4Illinois Department of Public Health, Springfield, IL, USA
5Illinois Department of Public Health, Chicago, IL, USA
(Accepted 31 March 2005, first published online 3 June 2005)
Cryptosporidium has become increasingly recognized as a pathogen responsible for outbreaks of
diarrhoeal illness in both immunocompetent and immunocompromised persons. In August 2001,
an Illinois hospital reported a cryptosporidiosis cluster potentially linked to a local waterpark.
There were 358 case-patients identified. We conducted community-based and waterpark-based
case-control studies to examine potential sources of the outbreak. We collected stool specimens
from ill persons and pool water samples for microscopy and molecular analysis. Laboratory-
confirmed case-patients (n=77) were more likely to have attended the waterpark [odds ratio (OR)
16.0, 95% confidence interval (CI) 3.8–66.8], had pool water in the mouth (OR 6.0,
95% CI 1.3–26.8), and swallowed pool water (OR 4.5, 95% CI 1.5–13.3) than age-matched
controls. Cryptosporidium was found in stool specimens and pool water samples. The chlorine
resistance of oocysts, frequent swimming exposures, high bather densities, heavy usage by diaper-
aged children, and increased recognition and reporting of outbreaks are likely to have
contributed to the increasing trend in number of swimming pool-associated outbreaks of
cryptosporidiosis. Recommendations for disease prevention include alteration of pool design to
separate toddler pool filtration systems from other pools. Implementation of education
programmes could reduce the risk of faecal contamination and disease transmission.
Cryptosporidium spp. (Cryptosporidium), a chlorine-
resistant protozoan parasite, was first identified as
a cause of illness in humans in 1976 . Since that
recognized as a pathogen responsible for outbreaks
of diarrhoeal illness in both immunocompetent and
* Author for correspondence: Dr L. M. Causer, Division of
Parasitic Diseases, National Center of Infectious Diseases, Centers
for Disease Control and Prevention, 4770 Buford Highway, NE,
Mailstop F-22, Atlanta, GA 30341, USA.
Use of trade names and commercial sources is for identification
only and does not imply endorsement by CDC or the U.S.
Department of Health and Human Services.
Data presented (poster) at the Annual Meeting of Infectious
Disease Society of America, 24–27 October 2002, Chicago, IL, and
51st Annual Epidemic Intelligence Service Conference, 22–26 April
2002, Atlanta, GA, USA.
Epidemiol. Infect. (2006), 134, 147–156.
f 2005 Cambridge University Press
Printed in the United Kingdom
be person-to-person, animal-to-animal, animal-to-
person, foodborne, and waterborne, and occurs
via the faecal–oral route with the ingestion of
viable oocysts . Reported outbreaks have been
associated with day-care centres [3–7], contaminated
drinking water [8, 9], food [10–12], and recreational
water facilities (both chlorinated and non-chlorinated
trend in the number of recreational water-associated
outbreaks of cryptosporidiosis suggesting a need for
public health efforts to be focused on improving the
understanding and prevention of this illness in aquatic
facilities. Swimming is enjoyed by adults and children
alike, and in the United States swimming is the second
most popular exercise activity with >360 million
annual visits to recreational water venues . The
chlorine resistance of Cryptosporidium, the frequent
exposures to swimming, high bather densities, and
heavy use by diaper-aged children who have a high
prevalence of Cryptosporidium  have all con-
tributed to this increasing trend in recreation water
facility-associated outbreaks. In addition, improved
recognition and increased reporting of such outbreaks
may play a role in contributing to this increasing
In this paper we report an outbreak of crypto-
poridiosis associated with a recreational waterpark
where transmission appears to have occurred de-
spite a well-maintained and managed swimming
On 13 August 2001, the Illinois Department of Public
Health (IDPH) was notified of a cluster of three
cases of diarrhoeal illness associated with exposure
to a recreational waterpark in central Illinois. Crypto-
sporidium was identified in stool samples of ill
patients. Following the collection of pool water
samples, the waterpark was closed and all pools
within the waterpark were hyperchlorinated (to main-
tain free chlorine levelsof 20 ppmfor 8 h)toinactivate
Cryptosporidium. An investigation of the outbreak
was conducted by Tazewell County Health Depart-
ment (TCHD), IDPH and CDC to confirm the
risk exposure and identify any additional risk
factors associated with illness. This research was
conducted in compliance with all applicable federal
regulations governing the protection of human sub-
A laboratory-confirmed case was defined as a person
living in or visiting central Illinois between 1 July and
31 August 2001 with a positive Cryptosporidium stool
test and at least one symptom of either diarrhoea,
vomiting, or abdominal cramps. A clinical case was
defined as a person living in or visiting central Illinois
between 1 July and 31 August 2001, with o1 day with
o3 loose (or watery) stools in 24 h. A control was de-
fined as a person living in or visiting central Illinois
toms of illness during the same time period. Controls
were matched by age and residential neighbourhood.
A descriptive study and two case-control studies
(community-based and waterpark-based) were con-
ducted. Through the local media and community
networks, ill persons were encouraged to contact
TCHD. In order to identify other potentially exposed
persons, case-patients were asked if there were any
other ill persons in their household or if anyone
attending the waterpark with them was ill. Matched
controls were identified by the following hierarchy
of methods: first, through case-patients (who were
asked to identify another healthy person within
5 years of their age), secondly through the local re-
verse-telephone directory based on residential address
of case-patients, and thirdly through canvassing local
schools and community groups. The majority of con-
trols were identified by the first and second methods.
A subset of the case-patients and matched controls
identified for the community-based case-control study
were included in the waterpark-based study.
A standardized telephone-administered question-
naire was used to collect information from potential
case-patients and controls regarding demographics,
symptoms of recent illness (within the previous
month), type of medical attention sought, and diag-
nostic tests performed. Case-patients o12 years of
age were interviewed directly while parents or guard-
ians of case-patients <12 years of age were inter-
viewed as a proxy. In addition, case-patients were
asked if they had recent exposure to persons with simi-
lar illness (or for controls, persons with diarrhoea).
Based on the case definition and the incubation period
for cryptosporidiosis, details of known risk exposures
during the 2 weeks prior to the onset of symptoms for
case-patients (and during a 2-week period between
148L. M. Causer and others
These included consumption of food and drinking
water, contact with young children, recent travel, and
any recreational water activities. When a recreational
water exposure was reported, specific waterpark-
related behaviours were explored. These included time
spent in the water, swimming in certain pools within
the park, getting water in the mouth, swallowing
water, diving into water, having the head under water,
using the waterslide, having water splashed into the
face, and consumption of food and beverages at the
The community-based, case-control study enrolled
all laboratory-confirmed case-patients and matched
controls. The waterpark-based, case-control study
limited enrolment to laboratory-confirmed case-
patients and controls with exposure to the waterpark
on 3 and 4 August, the days with the highest reported
Data were entered using Epi-Info, version 6.04
(CDC, Atlanta, GA, USA). Data analyses were per-
formed using SAS (SAS Institute Inc., Cary, NC,
USA). Odds ratios were calculated using conditional
logistic regression for matched pairs and x2tests were
used to test for statistical significance. Two-sided P
values <0.05 were deemed statistically significant.
Ill persons were encouraged to submit formalin-
preserved stool specimens for Cryptosporidium test-
ing. The local hospital laboratory in Tazewell County,
IDPH laboratory, and CDC, tested stool for
Cryptosporidium using the ProSpecT Cryptosporidium
USA), acid-fast staining, and microscopy. Positive
specimens were concentrated using the formalin-ethyl
acetatetechnique andthenconfirmed bythe Merifluor
(DFA) (Meridian Bioscience Inc., Cincinnati, OH,
USA). Potassium-dichromate-preserved stool speci-
mens were tested by CDC using DFA or polymerase
based polymerase chain reaction–restriction fragment
length polymorphism (PCR–RFLP) tool was used for
genotyping  and a PCR-sequencing tool based on
the 60 kDa glycoprotein (GP60) was used for sub-
The initial environmental assessment attempted to
determine likely routes for parasite contamination of
the pool and subsequent transmission, and to identify
any immediate remediable problems. The environ-
mental investigation included site visits to the water-
park, assessment of the procedures and practices of
the facility, evaluation of water sources, and the phys-
ical environment surrounding the waterpark. Infor-
mation on the occurrences of faecal accidents and
the responses of the pool management were reviewed
together with water chlorination, pH levels and filter
backwash records and procedures. Information was
collected concerning waterpark group rentals, foods
served at the concessions stand, dates and hours of
operation, bather load, water clarity, pool operation
and maintenance records, and pool design (including
filters, turnover, and chlorination equipment). Water-
quality data and treatment processes of the local
water-treatment facility, which distributes water to
the community in which the waterpark is located,
were also reviewed.
Prior to hyperchlorination of the pools at the
waterpark on 13 August 2001, pool water (10 l from
the toddler/wading pool, 10 l from the lap pool, and
10 l from the Lazy River) and backwash material (10 l
of a mix of water and diatomaceous earth filter media
from each filter) were collected for testing. These
samples were tested at CDC for Cryptosporidium
using USEPA Method 1622, which detects oocysts by
immunofluorescence after concentration of the water
sample using immunomagnetic beads to capture
oocysts . Samples also were tested by PCR [25, 26]
and with an electrochemiluminescence (ECL) antigen
From August 13 to 30 September 2001, a total of 358
case-patients (281 clinical cases and 77 laboratory-
confirmed) were identified by the investigation team.
Case-patients were predominantly children (77.9%
<18 years old; median 9 years; range 1–72 years).
Sixty-nine per cent of children were <12 years of age
and were interviewed by a proxy (parent or guardian).
Among the laboratory-confirmed case-patients, the
most commonly reported symptoms were diarrhoea
(94.8%), abdominal cramps (88.0%), and nausea
(76.4%). Symptoms among clinical case-patients were
similar (Table 1). More than half (63.2%) of the lab-
oratory-confirmed case-patients sought medical care,
and seven case-patients (9.0%) were hospitalized as
A Cryptosporidium outbreak at a recreational waterpark149
aresultoftheir illness. Hospitalized case-patientswere
6–71 years of age. The epidemic curve depicting
clinical and laboratory-confirmed cases by date of
symptom onset shows that transmission was occur-
ring from mid July to the end of August (Fig. 1).
Community-based case-control study
There were 77 case-patients and 77 matched controls
Exposures examined for association with cryptospor-
idiosis are presented in Table 2. Swimming at the
waterpark was strongly associated with crypto-
sporidiosis (OR 16.0, 95% CI 3.8–66.8). Having any
contact with a day-care centre (visiting or working at
a day-care centre or a child being in day care) was also
associated with illness (OR 6.0, 95% CI 1.3–26.8).
There appeared to be no statistically significant
association between consumption of drinking water
from any source (bottled, municipal or a private well)
Waterpark-based case-control study
Fifty case-patients and 50 matched controls were
enrolled in the waterpark-based case-control study.
Behaviours significantly associated with cryptospor-
idiosis were getting pool water in the mouth (OR 6.0,
95% CI 1.3–26.7) and swallowing pool water (OR
4.5, 95% CI 1.5–13.3) (Table 3). There was no sig-
nificant association with swimming in a particular
pool, or spending more than one cumulative hour in
the pool water.
Testing of formalin-preserved stool specimens sub-
mitted by symptomatic patients identified 77 positive
specimens (i.e. laboratory-confirmed case-patients).
In addition, 22 potassium-dichromate-preserved stool
specimens from symptomatic patients were examined.
Ten (45.5%) of these were positive by DFA and PCR
for Cryptosporidium. Genotyping revealed Crypto-
sporidium hominis (this species only infects humans)
in all PCR-positive individuals. Subtyping analysis
indicated that all of the 10 C. hominis-positive samples
had a parasite belonging to the subtype family Ia .
Results of the pool-water grab samples and back-
wash samples collected from the waterpark are pre-
sented in Table 4. All samples were PCR negative.
USEPA Method 1622 revealed Cryptosporidium
oocysts in the grab samples from the toddler/wading
pool and lap pool but not the Lazy River, and back-
wash from the toddler/lap/slide (not the river/tree
house backwash) filter system. ECL was positive for
both samples of filter backwash.
Figure 2 shows the layout of the main water features
of the waterpark. The waterpark consisted of a
toddler/wading pool (i.e. zero entry-level pool tran-
sitioning to a depth of 18 in.), a lap pool (depth of 3 ft
6 in. to 5 ft 0 in.), a ‘Lazy River’ (constant depth
along length of 2 ft 6 in.), one major slide/plunge pool
(depth of 2 ft 0 in. to 3 ft 6 in.) and three smaller slide/
plunge pools (depth 18 in.). There was no designated
diving pool. Child-oriented water features included a
tree house climbing structure and bucket drop and
several fountains and water sprays.
Male and female restrooms, both with showers and
diaper changing stations, were available within the
complex. A concessions outlet serving drinks and
snacks was also located within the pool area. The pool
complex was surrounded by a 6 ft high fence on three
sides and a building/entrance to the complex on the
fourth side. The waterpark was open every day of the
week, with restricted access for groups (including
swimming clubs, lessons, and private functions) in the
early mornings and late evenings.
The waterpark employed two diatomaceous earth
(DE) filtration systems; each with automated chlori-
nation pumps using liquid sodium hypochlorite,
12.5%. One DE system filtered water from the tod-
dler pool, lap pool and slide/plunge pools (estimated
water volume 200000 gallons; turnover 3.4 h), while
Table 1. Clinical symptoms and hospitalization from
cases identified in an outbreak of cryptosporidiosis,
Tazewell County, Illinois, 2001
confirmed casesClinical cases
* Denominator varies due to missing responses in ques-
150L. M. Causer and others
the other system filtered water from the Lazy River,
tree house and three small plunge pools (estimated
water volume 255000 gallons; turnover 2.8 h). All the
pools at the waterpark are heated to a set point of
28 xC. During peak times the waterpark generally has
a daily attendance of y1500 bathers. On 3 August
there were 1023 and on 4 August, a Saturday, there
were 1836 bathers.
The pool log records indicated that pH levels of the
chlorinated pool water were monitored 2–3 times per
day and recorded daily. No cyanurates were used.
Waterpark records indicated that one faecal or vomit
accident occurred approximately every 2 days. For
3 August there were two accidents recorded (one
faecal and one vomit both in the lap pool) and for 4
August there were no events recorded, although fur-
ther questioning of staff revealed there had been three
faecal accidents on that day. No distinction in the re-
cords was made between formed stool and diarrhoeal
Routine management of faecal accidents at the
waterpark appears to have followed CDC recom-
mendations for formed stool : removal of organic
material, check of free chlorine levels and if free
chlorine <2 ppm, then addition of chlorine to bring
level the chlorine level >2 ppm, and closure of the
pool to patrons for 20–30 min. No diarrhoeal acci-
dents were reported. Chlorine levels on 3 and 4
August were recorded as being >2 ppm in the lap
pool, toddler pool and the Lazy River. For all the
slide/plunge pools, chlorine levels were <2 ppm
(within acceptable levels of chlorine residual, accord-
ing to the Illinois Swimming Pool and Bathing Beach
code ). The pool records also mention the use of a
vacuum for cleaning the pool floor in some instances
after a faecal accident, a technique not recommended
by CDC as no uniform recommendations for dis-
infection of vacuum systems are available . Staff
reported no maintenance problems during the im-
mediate period prior to the outbreak. However, no
official maintenance logs were kept.
Water-quality data maintained at the local water
treatment facility that supplied the waterpark and the
surrounding community indicated the system was
operating within state regulations. The information
collected on food served at the pool and the source of
that food, did not reveal any additional information
considered pertinent to the investigation.
The outbreak described is the largest reported out-
break of cryptosporidiosis in Illinois. In recent years,
Illinois has reported between 90 and 126 cases of
cryptosporidiosis annually . The case-patients
associated with this outbreak resulted in the state
reporting a total of 483 cryptosporidiosis cases in
2001, the highest since reporting began in 1995. The
results of the epidemiological studies combined with
the results from the laboratory analyses of human
specimens and environmental samples suggest that
the source of the outbreak was human, and was likely
1 3 5 7 9
Date of symptom onset (2001)
11 13 15 17 19 21 23 25 27 29 31 2 4 68 10 12
14 16 18 20 22 24 26 28 30
No. of cases
Fig. 1. Epidemic curve showing laboratory-confirmed case-patients (&, n=77) and clinical case-patients (%, n=281) by
date of symptom onset.
A Cryptosporidium outbreak at a recreational waterpark 151
to have been the result of a diarrhoeal accident from
an infected individual swimming at the waterpark.
The epidemic curves illustrate that 9 August 2001
was the most frequent day for symptom onset and
that 3 August 2001 was the most frequent exposure
day. This is in keeping with the approximate 1-week
incubation period of cryptosporidiosis [32, 33] and is
further evidence that the outbreak was associated with
a visit to the waterpark. The associations between ill-
ness and swimming behaviours such as getting water
in the mouth and swallowing pool water confirm
previously reported risk behaviours .
There were a number of limitations and potential
biases resulting from the study design. Questionnaires
Table 2. Percent exposed, odds ratio (OR), and 95% confidence intervals (CI) for cryptosporidiosis risk
factors evaluated in the community case-control study, Tazewell County, Illinois, 2001
OR 95% CIn#
Other swimming facility
Private well water
Any contact with day-care centre$
Visited a day-care centre
Work at day-care
Child in day-care
Away from home5/73 6.9 4/6220.127.116.11–4.6
* All exposures occurred in the 2 weeks prior to symptom onset (case-patients) or in a 2-week period between 1 July and 31
August 2001 (controls).
# Denominator varies due to missing responses in questionnaire.
$ Visited a day-care centre, or worked at a day-care centre, or child was in day care.
Table 3. Percent exposed, odds ratio (OR), and 95% confidence intervals (CI) for risk factors for
cryptosporidiosis evaluated in the waterpark-based case-control study, Tazewell County, Illinois, 2001
Pool water in mouth
Swallowed pool water
Head under water
Water splashed in face
Dive into water
Use water slide
Use lap pool
Use wading pool
Use ‘Lazy River’
<1 h in the water
Eat concession stand food
Drinks with ice
Drink from water fountain
* Denominator varies due to missing responses in questionnaire.
152 L. M. Causer and others
were administered in some cases more than 1–2 weeks
after symptoms had resolved, and in the case of chil-
dren (<12 years of age), questionnaires were ad-
ministered to parents/caregivers as a proxy for the
child. These techniques may have resulted in infor-
mation bias, however, as case-patients and controls
were asked to recall similar time periods in the past, it
is unlikely that recall bias would have been differential
between the two groups. Similarly, the reporting of
behaviours by proxy is unlikely to have influenced
the associations found as controls were matched
for age. As a result of a variety of publications in
the local media related to the outbreak and the
implicated waterpark, case-patients and controls
may have been aware of the investigation hypothesis,
introducing selection bias and possibly contributing
to the strength of the association found in the com-
munity-based study. Selection bias may also have
been introduced as a result of the methodology
employed to recruit controls for this study. These
selection biases are less likely to have influenced the
behavioural associations found in the waterpark-
The presence of Cryptosporidium oocysts in the
pool waterandbackwash samplesarefurther evidence
that the waterpark pools contained the parasite and
were associated with this outbreak. However, none of
the tests performed on these pool samples indicates
whether the oocysts detected were infectious. ECL
relies on the detection of soluble antigen on the
Fig. 2. Layout of waterpark associated with Cryptosporidium outbreak, Illinois, 2001.
Table 4. Water and diatomaceous earth (DE) backwash samples, results
from USEPA method 1622, ECL and PCR testing
method 1622 ECL PCR
DE backwash samples
(Lazy River/tree house)
n.t., Not tested.
A Cryptosporidium outbreak at a recreational waterpark153
surface of the oocyst and provides a numeric
approximation of oocysts present, while USEPA
Method 1622 testing involves recognition of primarily
intact oocysts. Discordant results between ECL and
USEPA Method 1622 on the backwash samples may
be explained by the higher sensitivity of ECL than
DFA. ECL is an environmental research tool that was
originally developed for testing of source or drinking
water, and later was applied for oocyst detection in
environmental and stool samples. As this method is
still being refined and has not yet been standardized,
results should be interpreted with caution. In
addition, although these water assays are specific they
are insensitive and large-volume water testing poses a
substantial challenge during the investigation of such
The interconnected design of the pools with shared
filtration systems may have contributed to the con-
tamination of multiple pools within the waterpark.
Pool water disinfection and filtration systems are
widely used to prevent such contamination, however,
Cryptosporidium is a chlorine-resistant parasite 
and standard swimming-pool chlorine concentrations
(1–5 mg/l) are not effective in immediately inactivat-
ing Cryptosporidium oocysts. Thus, the organism may
survive for days in the pool water . In addition,
due to the small size of the oocysts (4–6 mm) ,
Cryptosporidium is not effectively removed by fil-
tration systems usually employed in recreational
water facilities. Even DE filters that are designed for
swimming pool use (because pore size decreases
dramatically as the filter removes debris), are not able
to fully remove Cryptosporidium oocysts from swim-
ming pool water in a short period of time .
Although this outbreak was not necessarily due
to poor pool maintenance, deficient maintenance is
reported to be widespread in pools nationwide .
The findings of this investigation suggest that even
a waterpark complying with existing standards and
guidelines may become contaminated with Crypto-
sporidium oocysts and be involved in an outbreak.
The characteristics of the parasite, the limited effec-
tiveness of pool hardware to remove Cryptosporidium
oocysts, and the relatively small infective dose of
Cryptosporidium , makes it important to focus on
other preventive strategies to further reduce the risk
of transmission of cryptosporidiosis. Strategies need
to focus on educating and modifying behaviours of
pool managers, staff, and patrons to reduce the risk
of both contamination of pool water and transmission
For pool management, the importance of a rapid
and adequate response to known and suspected faecal
contaminationeventsshould be emphasized. Manage-
ment of faecal and diarrhoeal episodes should adhere
to CDC recommended guidelines and should include
hyperchlorination for a time period that equates to
a contact time (CT) inactivation value of 9600 (e.g.
free chlorine levels of 20 ppm for 8 h) . Pool
management and staff should ensure the facility
complies with current codes and standards of oper-
ation and insist on patrons’ adherence with regu-
lations and practice of good hygiene when using the
Modification of waterpark design may also help
prevent cross-contamination of pools leading to
expanded transmission of Cryptosporidium. Such de-
sign modifications include separation of the wading/
toddler pool filtration system from other facility
swimming pools to avoid the potential for cross-
contamination and increasing the turnover rate of the
toddler pool to y30 min. Modification of filtration
systems may also be appropriate. As a result of this
outbreak and investigation, the waterpark installed
an ultraviolet system to complement the existing
chlorine pool water disinfection and DE filtration
process. Ultraviolet treatment of water effectively
inactivates Cryptosporidium oocysts [34, 38, 39].
Public education and patron behaviour modifi-
cation are also critical to reduce the risk of illness.
Simple messages to encourage good hygiene are key.
Encouraging parents and guardians to insist on the
avoidance of swimming while symptomatic with di-
arrhoea and during outbreaks for 2 weeks following
resolution of symptoms, to avoid risk behaviours such
as getting pool water in the mouth and swallowing
pool water, to ensure frequent bathroom breaks for
children and toddlers, and to conduct appropriate
diaper changing and hand washing are behaviours
that are likely to prevent pool water contamination
and transmission of cryptosporidiosis, as well as other
illness such as giardiasis and shigellosis.
Early recognition of outbreaks and prompt action
by local health departments may help to limit the
extent of the outbreak. Early notification by staff at
the local hospital, the rapid response by TCHD in
implementation of prevention messages, and hyper-
chlorination of the pool water may have limited the
extent of this outbreak. No secondary laboratory-
confirmed cases were identified, nor was there sub-
stantial evidence of such cases among the clinical
154 L. M. Causer and others
cases, suggesting that efforts to educate the public
and disseminate prevention messages such as hand
washing and avoidance of swimming while ill and for
2 weeks following illness may have been effective.
TCHD also made substantial efforts during the 2001
swimming season to educate the community and to
highlight the public health importance of increasing
efforts to keep ill persons and persons recovering from
in the community were notified of the outbreak early
on as were day-care centres. Without early notifi-
cation about outbreaks and implementation of pre-
vention measures, satellite pool locations have been
known to account for amplification and perpetuation
of such outbreaks .
Although outbreaks are more likely to be reported
in the literature, it is important to consider these in
relation to the background of sporadic cryptospor-
idiosis occurring in the United States, particularly
as sporadic cases of cryptosporidiosis are thought to
account for the majority of reported cases . From
a public health perspective, the risk factors associated
with sporadic cases are similar to those previously
seen among immunocompromised and outbreak-
related cases-patients suggesting that health providers
and the public need to be aware of the multiple modes
of transmission in order to have a substantial impact
on the disease .
Protecting patrons and bathers from transmissible
illnesses such as cryptosporidiosis is in the interest of
both pool management and public health. Public
health agencies may want to consider what change in
number of cases reported through their local surveil-
lance system requires the implementation of measures
to halt further transmission. Achieving a safe swim-
ming environment requires a combination of efforts
by individuals and the community. For further CDC
recommendations for swimmers, pool operators, and
public health officials see ref. .
Practitioner, and staff in the Pekin Hospital Labora-
tory for their astute recognition and rapid reporting
of the first cases to the Tazewell County Health
Department (TCHD) and assistance with follow-up
activities. We gratefully acknowledge all the staff at
TCHD who helped with the administration of our
questionnaires, data management, and patient follow-
up. We also thank the Illinois Department of Public
thankJudy Conway, Infection Control
Health, Division of Laboratories for their assistance
with processing of specimens. All funding for this
evaluation was provided by Centers for Disease
Control and Prevention, Tazewell County Health
Department, and the Illinois Department of Public
1. Nime F, Burek J, Page D, Holscher M, Yardley J. Acute
enterocolitis in a human being infected with the proto-
zoan Cryptosporidium. Gastroenterology 1976; 70:
2. Fayer R, Morgan UM, Upton SJ. Epidemiology of
Cryptosporidium: transmission, detection and identifi-
cation. Int J Parasitol 2000; 30: 1305–1322.
3. Centers for Disease Control and Prevention. Crypto-
sporidiosis among children attending day-care centers:
Georgia, Pennsylvania, Michigan, California, New
Mexico. Morb Mortal Wkly Rep 1984; 33: 509–601.
4. Alpert G, Bell LM, Kirkpatrick CE, et al. Outbreak of
cryptosporidiosis in a day-care center. Pediatrics 1986;
5. Tangermann RH, Gordon S, Wiesner P, Kreckman L.
An outbreak of cryptosporidiosis in a day-care center
in Georgia. Am J Epidemiol 1991; 133: 471–476.
6. Skeels M, Sokolow R, Hubbard C, Andrus J, Baisch J.
Cryptosporidium infection in Oregon public health clinic
patients 1985–88: the value of statewide laboratory
surveillance. Am J Public Health 1990; 80: 305–308.
7. Cordell RL, Addiss DG. Cryptosporidiosis in child care
settings: a review of the literature and recommendations
for prevention and control. Pediatr Infect Dis J 1994;
8. MacKenzie WR, Hoxie NJ, Proctor ME, et al. A mass-
ive outbreak in Milwaukee of Cryptosporidium infection
transmitted through the public water supply. N Engl J
Med 1994; 331: 161–167.
9. Hayes EB, Matte TD, O’Brien TR, et al. Large com-
munity outbreak of cryptosporidiosis due to contami-
nation of a filtered public water supply. N Engl J Med
1989; 320: 1372–1376.
10. Millard PS, Gensheimer KF, Addiss DG, et al. An out-
break of cryptosporidiosis from fresh-pressed apple
cider. J Am Med Assoc 1994; 272: 1592–1596.
11. Centers for Disease Control and Prevention. Foodborne
outbreak of cryptosporidiosis – Spokane, Washington,
1997. Morb Mortal Wkly Rep 1998; 47: 565–567.
12. Centers for Disease Control and Prevention. Foodborne
Cryptosporidiumparvum – Minnesota,
Mortal Wkly Rep 1996; 45: 783–784.
13. Baker M, Russell N, Roseveare C, O’Hallahan J, Palmer
S, Bichan A. Outbreak of cryptosporidiosis linked to
Hutt Valley swimming pool. NZ Public Health Rep
14. Centers for Disease Control and Prevention. Crypto-
sporidium infections associated with swimming pools –
A Cryptosporidium outbreak at a recreational waterpark155
Dane County, Winconsin, 1993. Morb Mortal Wkly Download full-text
Rep 1994; 43: 561–563.
15. Centers for Disease Control and Prevention. Outbreak of
gastroenteritis associated with an interactive water
fountain at a beachside park – Florida, 1999. Morb
Mortal Wkly Rep 2000; 49: 565–568.
16. Centers for Disease Control and Prevention. Protracted
outbreaks of cryptosporidiosis associated with swim-
ming pool use – Ohio and Nebraska, 2000. Morb
Mortal Wkly Rep 2001; 50: 406–410.
17. Centers for Disease Control and Prevention. Outbreak of
cryptosporidiosis associated with a water sprinkler
fountain – Minnesota, 1997. Morb Mortal Wkly Rep
1998; 47: 856–860.
18. Sorvillo FJ, Fujioka K, Nahlen B, Tormey MP,
Kebabjian R, Mascola L. Swimming-associated crypto-
sporidiosis. Am J Public Health 1992; 82: 742–744.
19. Sundkvist T, Dryden M, Gabb R, Soltanpoor N,
Casemore D, Stuart J. Outbreak of cryptosporidiosis
associated with a swimming pool in Andover. Commun
Dis Rep CDR Rev 1997; 7: R190–192.
20. US Bureau of the Census. Statistical abstract of the
United States – 1995, 115th edn. Washington, DC: US
Bureau of the Census, 1995.
21. Meinhardt PL, Casemore DP, Miller KB. Epidemiologic
aspects of human cryptosporidiosis and the role of
waterborne transmission. Epidemiol Rev 1996; 18:
22. Xiao L, Bern C, Limor J, et al. Identification of 5 types
of Cryptosporidium parasites in children in Lima, Peru.
J Infect Dis 2001; 183: 492–497.
23. Alves M, Xiao L, Sulaiman I, Lal AA, Matos O, Antunes
F. Subgenotype analysis of Cryptosporidium isolates
from humans, cattle, and zoo ruminants in Portugal.
J Clin Microbiol 2003; 41: 2744–2747.
24. US Environmental Protection Agency. Method 1622:
Cryptosporidium and Giardia in water by filtration/
IMS/FA. Washington, DC, USA: Office of Research
and Development, US Government Printing Office,
25. Xiao L, Alderisio K, Limor J, Royer M, Lal A.
Identification of species and sources of Cryptosporidium
oocysts in storm waters with a small-subunit rRNA-
based diagnostic and genotyping tool. Appl Environ
Microbiol 2000; 66: 5492–5498.
26. Xiao L, Singh A, Limor J, Graczyk TK, Gradus S, Lal
A. Molecular characterization of Cryptosporidium
oocysts in samples of raw surface water and wastewater.
Appl Environ Microbiol 2001; 67: 1097–1101.
27. Lee Y-M, Johnson PW, Call JL, et al. Development and
application of a quantitative, specific assay for Crypto-
sporidium parvum oocyst detection in high-turbidity
environmental water samples. Am J Trop Med Hyg
2001; 65: 1–9.
28. Strong WB, Gut J, Nelson RG. Cloning and sequence
analysis of a highly polymorphic Cryptosporidium
parvum gene encoding a 60-kilodalton glycoprotein
and characterization of its 15- and 45-kilodalton zoite
surface antigen products. Infect Immun 2000; 68:
29. Centers for Disease Control and Prevention. Notice to
Readers: responding to fecal accidents in disinfected
swimming venues. Morb Mortal Wkly Rep 2001; 50:
30. Joint Committee on Administrative Rules. Title 77:
Public Health, Chapter 1: Department of Public
Health, Part 820 Illinois Swimming Pool and Bathing
Beach Code, Section 820.320 Water Quality http://
077008200D03200R.html). Accessed 5 January 2003.
31. Centers for Disease Control and Prevention. Crypto-
sporidiosissurveillance – United
Morb Mortal Wkly Rep SS-1 2005; 54: 1–8.
32. Navin T, Juranek D. Cryptosporidiosis: clinical, epi-
demiologic, and parasitologic review. Rev Infect Dis
1984; 6: 313–327.
33. Jokipii L, Jokipii A. Timing of symptoms and oocyst
excretion in human cryptosporidiosis. N Engl J Med
1986; 315: 1643–1647.
34. Korich DG, Mead JR, Madore MS, Sinclair Na, Sterling
CR. Effects of ozone, chlorine dioxide, chlorine, and
monochloramine on Cryptosporidium parvum oocyst
viability. Appl Environ Microbiol 1990; 56: 1423–1428.
35. Schuler P, Ghosh M. Diatomaceous earth filtration of
cysts and other particulates using chemical additives.
J Am Water Works Assoc 1990; 82: 67–75.
36. Centers for Disease Control and Prevention. Surveillance
data from swimming pool inspections – selected states
and counties, United States, May–September 2002.
Morb Mortal Wkly Rep 2003; 52: 513–516.
37. Dupont HL, Chappell CL, Sterling CR, Okhuysen PC,
Rose JB, Jakubowski W. The infectivity of Crypto-
sporidium parvum in healthy volunteers. N Engl J
Med 1995; 332: 855–859.
38. Corona-Vasquez B, Samuelson A, Rennecker JL,
Marinas B. Inactivation of Cryptosporidium parvum
oocysts with ozone and free chlorine. Water Research
2002; 36: 4053–4063.
39. Li H, Finch G, Smith D, Belosevic M. Sequential
inactivation of Cryptosporidium parvum using ozone
and chlorine. Water Res 2001; 35: 4339–4348.
40. Dietz V, Vugia D, Nelson J, et al. Active, multisite,
parvum. Am J Trop Med Hyg 2000; 62: 368–372.
41. Roy SL, Delong SM, Stenzel SA, et al. Risk factors for
sporadic cryptosporidiosis among immuocompetent
persons in the United States from 1999 to 2001. J Clin
Microbiol 2004; 42: 2944–2951.
42. Centers for Disease Control and Prevention. Division
of Parasitic Diseases. Healthy swimming (http://
www.cdc.gov/healthyswimming/). CDC, Atlanta, GA,
2005. Accessed 5 January 2003.
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