a1 Division of Sexually Transmitted Diseases and HIV Prevention, National Center for Prevention Services, Centers for Disease Control and Prevention, Atlanta, GA, USA
a2 Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA
a3 City of Milwaukee Department of Health, Milwaukee, WI, USA
a4 Bureau of Public Health, Wisconsin Division of Health, Madison, WI, USA
During March–April 1993, an estimated 403000 residents of the 5-county greater Milwaukee, Wisconsin area developed cryptosporidiosis after drinking contaminated municipal water. Although the number of cases dropped precipitously after the implicated water plant closed on 9 April, cases continued to occur. To investigate risk factors for post-outbreak cryptosporidiosis, 33 Milwaukee-area residents who had laboratory-confirmed Cryptosporidium infection with onset of diarrhoea between 1 May and 27 June 1993 were interviewed by telephone. Of these, 28(85%) had onset of diarrhoea during May, 12(36%) had watery diarrhoea during the outbreak, and 5 (15%) were HIV-infected. In a neighbourhood-matched case-control study, immunosuppression (matched odds ratio (MOR) not calculable, 95 % confidence interval (CI) 3·0, infinity) and having a child less than 5 years old in the household (MOR = 17·0, CI 2·0, 395·0) were independently associated with infection. When persons who had diarrhoea during the outbreak were excluded, immunosuppression remained significantly associated with illness (MOR not calculable, CI 1·6, infinity). Cryptosporidium transmission continued after this massive waterborne outbreak but decreased rapidly within 2 months.
(Accepted April 04 1996)
c1 David Addiss, Division of Parasitic Diseases, Mailstop F-22, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA.