It wasn't until the spring of 1993 that cryptosporidiosis gained national attention after 400,000 people in Milwaukee became ill with diarrhea after drinking water that contained this parasite. The most common symptom is water diarrhea. Other signs and symptoms include weight loss, stomach cramps, nausea, vomiting, headache and low-grade fever. These symptoms usually appear within 2 to 14 days of swallowing the parasite. Some people might not have any symptoms at all.
Infection occurs after the parasite is swallowed.
Fecal-oral spread can also occur by drinking contaminated water, but this is less likely. In rare cases, cryptosporidiosis can spread through lakes and swimming pools when people who have diarrhea swim in the lake or pool. The parasites can live in the water and infect other swimmers who swallow it or get their lips wet. Anyone can get a cryptosporidium infection. People at greatest risk for severe illness are those with weakened immune systems such as people with HIV infection, on chemotherapy or on high-dose steroid therapy after organ transplantation.