On April 3, 1993, the emergency room of a hospital in Milwaukee, Wisconsin, was overwhelmed with patients complaining of diarrhea. Two weeks after the outbreak, the source of the disease was identified as tap water supplied by the Milwaukee Southern Waterworks, and the causative pathogen was found to be Cryptosporidium. It was estimated that approximately 52% of the residents who consumed the tap water were infected. While some individuals experienced only mild symptoms, such as loss of appetite, about 403,000 people suffered severe symptoms, including abdominal pain, diarrhea, and vomiting. Among them, approximately 4,400 were hospitalized and 109 died.