In April 1993, the Commissioner of Health was astonished when businesses throughout Milwaukee, Wisconsin were closing down due to large numbers of people reporting symptoms of gastrointestinal illnesses. Eventually, more than 400,000 of the city's 1.6 million people became ill and several people died. A waterborne parasite, cryptosporidium, was identified as the culprit after analysis of stools and water supplies. It was discovered that the city’s sewage treatment outlet was too close to one of the city’s water sources. The mayor quickly issued a boil water advisory that seemed to stop the outbreaks. This was the largest waterborne disease outbreak ever documented in the United States.
