One team originated with the Centers for Disease Control and Prevention (CDC), which dispatched Epidemic Intelligence Service (EIS) officers to the scene to help in the investigation. In the days and weeks that followed, 11 investigatory teams studied the outbreak to document the largest waterborne outbreak to ever hit the U.S. The public water supply for the more than 800,000 residents was contaminated putting the those who were immunocompromised at the greatest risk. On April 7, 60 hours after the first indication of the outbreak, the mayor issued a water advisory, which included boiling of all water used for consumption. It was on day three of this outbreak that the first positive test for Cryptosporidium was found in stool samples. The department determined much higher rates of emergency room visits for GI distress and a larger number of tests ordered for enteric diseases.
Responding to this information, the health commissioner began calling local hospital microbiology laboratories and emergency rooms to determine the extent of the GI illness around the city. The chief virologist and the commissioner of health received calls from worried residents and the press inquiring about reports of widespread gastrointestinal (GI) illness among residents. Row after row of anti-diarrheal mediations were missing from shelves, bought up in a frenzy by citizens suffering from acute abdominal pain, diarrhea, vomiting, and fever. If you lived in Milwaukee in early April 1993, you would have found an unusual sight in many of the pharmacies around town.