Multivariate Analysis of Risk Factors Associated with a Community Outbreak of Cryptosporidiosis in Kansas, 2003 Open Access

Brou, Lina (2012)

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Multivariate Analysis of Risk Factors Associated with a Community Outbreak of
Cryptosporidiosis in Kansas, 2003

By Lina Brou
Background: The chlorine-resistant protozoan, Cryptosporidium, commonly associated with
daycare and swimming facilities, has emerged as the leading known cause of recreational waterborne
diarrhea outbreaks in the United States. In the summer of 2003, an outbreak of cryptosporidiosis
occurred among residents of one county in Kansas.
Methods: To determine the magnitude of the outbreak and identify risk factors for infection, we
performed a secondary analysis of a county-wide matched case-control interview study. Subjects
included laboratory-confirmed cryptosporidiosis cases (n=63), a random sample of clinical cases
(n=88), and age-matched controls identified by random-digit dialing (n=302). Clinical
cryptosporidiosis was defined as diarrhea (≥3 loose stools in a 24 hour period) for ≥ 3 days within a
one week period after June 15, 2003. Conditional logistic regression was the primary statistical
methodology used.
Results: The final model included the following predictors: treated recreational water (adjusted
matched odds ratio = 7.753; 95% CI = 3.577, 16.804; p-value <0.0001), having a child in childcare
outside of the home (amOR = 3.609; 95% CI = 1.69, 7.709; p-value = 0.0009), and having a
household contact with diarrhea (amOR = 10.575; 95% CI = 5.102, 21.916; p-value<0.0001). To
identify which facilities could be implicated, a second model resulted in the following predictors:
Swimming Pool D (amOR = 4.324; 95% CI = 1.087, 17.209; p-value = 0.0377); Daycare 2 wading
pool (amOR = 19.475; 95% CI = 2.719, 139.464; p-value = 0.0031); and having a household contact
with diarrhea (amOR = 7.914; 95%CI = 2.744, 22.821; p-value = 0.0001). No interaction terms were
significant and there was no indication of collinearity.
Discussion: This is one of the largest reported U.S. community-wide cryptosporidiosis outbreaks
and the first outbreak associated with this Cryptosporidium subtype. Although the original source of
the outbreak was identified as a single contaminated swimming pool, the outbreak spread throughout
the community via secondary and tertiary exposures (i.e., daycare exposure and person-to-person
contact). It draws attention to the need for collaborative efforts between local, state, and federal
agencies to define and develop policies that facilitate prompt intervention to prevent community-
wide transmission of Cryptosporidium.

Table of Contents

Table of Contents

1. Background 1

1.1 Epidemiology 3
1.2 Pathogen 4
1.3 Environment 5
1.4 Human Cryptosporidiosis 6
1.5 Risk Factors in Cryptosporidiosis Outbreaks 7

2. Manuscript 13

2.1 Introduction 13
2.2 Methods 16
2.3 Results 19
2.4 Discussion 21
2.5 References 26
2.6 Tables and Figures 36

3 . Public Health Implications 42

4. Appendix A: Additional Tables 44

5. Appendix B: Case Questionnaire 48

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