Cryptosporidium can cause gastrointestinal illness (e.g., diarrhea, vomiting, cramps). The most common symptom of cryptosporidiosis (the clinical disease caused by Cryptosporidium) is watery diarrhea. Symptoms of cryptosporidiosis generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite. Symptoms usually last about 1 to 2 weeks (with a range of a few days to 4 or more weeks) in persons with healthy immune systems. People with weakened immune systems may develop serious chronic, and sometimes fatal illness. Some people with Cryptosporidium will have no symptoms. Information on appropriate means to lessen the risk of infection from Cryptosporidium and other microbial contaminants is available online by clicking here.