The usual sources of cryptosporidial contamination of drinking water are human sewage (e.g., sewage system overflows) and runoff carrying animal waste (e.g., from dairy farms). Although coagulation-sedimentation and filtration reduce the levels of cryptosporidium in water supplies, they do not eliminate it. Chlorination has no effect on the organism, which protects itself in the form of an oocyst, a tiny encapsulated egglike structure, when not in the intestine of an animal or human, but ozone disinfection has been more successful. Cryptosporidiosis affected more that 400,000 people and caused over 60 deaths in Milwaukee in 1993 when the parasites contaminated the public water system. Smaller outbreaks have occurred in other states.
See also water pollution .
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