1993 Milwaukee Cryptosporidiosis outbreak
The 1993 Milwaukee Cryptosporidiosis outbreak was a significant distribution of the Cryptosporidium protozoan in Milwaukee, Wisconsin, and the largest waterborne disease outbreak in documented United States history. The Howard Avenue Water Purification Plant (see Town of Lake water tower) was contaminated, and treated water showed turbidity levels well above normal. It was one of two water treatment plants for Milwaukee. The root cause of epidemic was never officially identified; initially it was suspected to be caused by the cattle genotype due to runoff from pastures.  It was also thought that melting ice and snowmelt carrying Cryptosporidium may have entered the water treatment plants through Lake Michigan.  MacKenzie et al. and the CDC showed that this outbreak was caused by Cryptosporidium oocysts that passed through the filtration system of one of the city's water-treatment plants, arising from a sewage treatment plant's outlet 2 miles upstream in Lake Michigan.
This abnormal condition at the water purification plant lasted from March 23 through April 8, after which, the plant was shut down. Over the span of approximately two weeks, 403,000 of an estimated 1.61 million residents in the Milwaukee area (of which 880,000 were served by the malfunctioning treatment plant) became ill with the stomach cramps, fever, diarrhea and dehydration caused by the pathogen. At least 104 deaths have been attributed to this outbreak, mostly among the elderly and immunocompromised people, such as AIDS patients.
- MacKenzie WR, Hoxie NJ, Proctor ME, Gradus MS, Blair KA, Peterson DE; et al. (1994). "A massive outbreak in Milwaukee of Cryptosporidium infection transmitted through the public water supply". N Engl J Med 331: 161–7. doi:10.1056/nejm199407213310304.
- Botkin and Keller (2005). Environmental Science, Earth as a Living Planet, 5th Edition. p. 441.
- Neil J. Hoxie; et al. (December 1997), "Cryptosporidiosis-Associated Mortality Following a Massive Waterbome Outbreak in Milwaukee, Wisconsin", American Journal of Public Health 87 (12): 2032–2035, doi:10.2105/ajph.87.12.2032, PMC 1381251, PMID 9431298
- Cryptosporidium and public health (Drinking Water and Health Newsletter)
- Cost of Illness in the 1993 Waterborne Cryptosporidium Outbreak, Milwaukee, Wisconsin (CDC)
- Cryptosporidium: A Risk to Our Drinking Water (Wisconsin DNR)
- Graphic Presentation of the Milwaukee Cryptosporidium Outbreak (CDC)
- A Massive Outbreak in Milwaukee of Cryptosporidium Infection Transmitted through the Public Water Supply (New England Journal of Medicine)