DID MILWAUKEE EXPERIENCE WATERBORNE CRYPTOSPORIDIOSIS BEFORE THE LARGE DOCUMENTED OUTBREAK IN 1993

The patterns of incidence and pathways of spread for cryptosporidiosis are poorly understood. In this study, we explored the possibility tha t drinking water caused significant waterborne cryptosporidiosis in Mi lwaukee well before the massive documented outbreak in April 1993. We generated time series of dairy counts of emergency room visits and hos pital admissions for gastroenteritis in Milwaukee using the billing re cords of the Medical College of Wisconsin for January 1, 1992, through May 3, 1993. The Milwaukee Water Works provided us with data on drink ing water turbidity for the same period. The service area of the South Plant experienced a sharp rise in turbidity just before the outbreak. During the outbreak period, gastroenteritis events were most strongly associated with turbidity at a lag of 7 days in children and 8 days i n adults. It is reasonable to conclude that these lag times reflect th e incubation period of Cryptosporidium. During the 434 days before the outbreak, gastroenteritis events were most strongly associated with t urbidity at a lag of 8 days among children and 9 days among adults in the servile area of the North Plant, the plant that experienced the hi ghest effluent turbidity during this period. These findings are consis tent with the conclusion that waterborne cryptosporidiosis was occurri ng in Milwaukee for more than a year before the documented outbreak.