Summary
Highlights
In the spring of 1993, Milwaukee, Wisconsin, faced an unexplained outbreak of severe gastrointestinal illness. Over 400,000 residents fell ill, 4,000 were hospitalized, and more than 100 people died. Initial suspicions of influenza or common bacterial infections like shigella or salmonella proved negative. The illness disproportionately affected individuals with weakened immune systems, such as infants, the elderly, cancer patients, and those with HIV/AIDS, including four-year-old Becky Furmann and 40-year-old Antonio Claudio, whose symptoms were particularly severe and persistent.
Health officials were baffled as no common food source could be identified. Stool samples showed no known bacteria. The geographic distribution of cases, largely clustered in Milwaukee's south side, suggested something specific to that area. While municipal water quality records initially showed levels within EPA guidelines, a peak in turbidity (foreign particles) was noted in the south side's water plant a week before the outbreak. This raised concerns about water contamination, especially since chlorine-based disinfection might not be effective against an unknown contaminant, putting the city and its major industries, like brewing, at risk.
A microbiologist, Sandy Schroederus, at a local hospital, decided to perform an acid-fast stain on stool samples, a less common test for parasites not visible with standard iodine stains. Her initiative led to the discovery of Cryptosporidium, a single-celled protozoan parasite. This organism multiplies rapidly in the gastrointestinal system, causing severe cramps and diarrhea by preventing fluid retention. While healthy individuals typically recover within a week, it can be deadly for those with compromised immune systems. This discovery confirmed the agent behind the widespread illness and implicated the city's water supply.
Upon learning of the Cryptosporidium discovery and Dr. Jeffrey Davis, the state epidemiologist's reluctance to drink tap water, Milwaukee's mayor issued a bold boil water advisory for at least five minutes, impacting dental offices, restaurants, and daily life. Subsequent independent lab tests confirmed Cryptosporidium in the purified water from the Howard Avenue Water Plant, which was then closed for disinfection. The contamination was particularly terrifying for individuals with HIV/AIDS, for whom cryptosporidiosis was often a death sentence. Antonio Claudio continues to suffer from chronic diarrhea, and Becky Furmann sadly succumbed to the illness.
Investigators initially theorized that heavy rains and snowmelt in April 1993 caused agricultural runoff containing Cryptosporidium from farm animal manure to enter Lake Michigan, a source of Milwaukee's drinking water. However, four years later, DNA testing on Cryptosporidium samples revealed a shocking truth: the strain came from human waste, not farm animals. It was traced to a sewage treatment plant's overflow valve less than two miles upstream from the Howard Avenue Water Plant's intake in Lake Michigan. Today, sewage is no longer released into the lake, the water plant's intake was moved, and Milwaukee is building an ozonization facility, employing a disinfection method known to kill Cryptosporidium, to prevent such a tragedy from recurring. The event spurred other cities to re-evaluate their water safety measures.