Journal Article

The Role of Disease Transmission and Conferred Immunity in Outbreaks: Analysis of the 1993 <i>Cryptosporidium</i> Outbreak in Milwaukee, Wisconsin

Joseph N. S. Eisenberg, Xiudong Lei, Alan H. Hubbard, M. Alan Brookhart and John M. Colford

in American Journal of Epidemiology

Published on behalf of Johns Hopkins Bloomberg School of Public Health

Volume 161, issue 1, pages 62-72
Published in print January 2005 | ISSN: 0002-9262
Published online January 2005 | e-ISSN: 1476-6256 | DOI:
The Role of Disease Transmission and Conferred Immunity in Outbreaks: Analysis of the 1993 Cryptosporidium Outbreak in Milwaukee, Wisconsin

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The authors examined two competing hypotheses regarding the cause of the 1993 Cryptosporidium outbreak in Milwaukee, Wisconsin. The first was that oocyst contamination of the drinking-water influent, coupled with a treatment plant failure, resulted in a point-source outbreak. The second was that the outbreak was the result of transmission processes that amplified the oocyst concentration in the drinking-water effluent. Analysis of the model suggested that 1) transmission directly from person to person contributed 10% (95% confidence interval: 6%, 21%) of the total cases; 2) closing the drinking-water plant prevented 19% (95% confidence interval: 17%, 21%) of the additional cases of disease that occurred compared with the scenario in which the plant had not been closed, a result primarily driven by conferred immunity that resulted in depletion of the susceptible population; and 3) the outbreak was caused by a transmission cycle due to infectious persons shedding pathogens into the sewage, environmental transport of these pathogens via Lake Michigan to the drinking-water plant, and infection of susceptible persons via exposure to drinking water. The incidence data were consistent with this hypothesis. Further simulations suggested that increasing the distance between the wastewater effluent and the drinking-water influent may have prevented the outbreak.

Keywords: Cryptosporidium; disease outbreaks; disease transmission; drinking; models, theoretical; water; CI, confidence interval; MH, Metropolis-Hastings; MLE, maximum likelihood estimate.

Journal Article.  5784 words.  Illustrated.

Subjects: Public Health and Epidemiology

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