Cryptosporidium species can infect humans and other mammals. Infection occurs through consumption of fecally contaminated water or food or through close person-to-person or animal-to-person transmission. Municipal water supplies and swimming pools can be a source of infection because the thick-walled oocysts are chlorine resistant and can evade filtration. This parasite is highly infectious; ingestion of fewer than 50 oocysts may result in infection. The incubation period is 7 days. Although some infected patients will be asymptomatic, symptomatic patients typically report watery diarrhea, crampy abdominal pain, nausea, vomiting, malaise, fever, dehydration, and weight loss. Symptoms usually last less than 2 weeks before spontaneously resolving in immunocompetent hosts. Immunocompromised patients, in particular patients with AIDS, can develop serious and prolonged infection. Diagnosis can be established microscopically by visualization of oocysts with modified acid-fast staining, molecular testing, and enzyme or direct fluorescent immunoassay testing. Treatment for immunocompetent patients usually consists of supportive care. When antimicrobial agents are considered for severe or prolonged infection, nitazoxanide is recommended. In HIV-infected patients, antiretroviral therapy is most effective in resolving infection. Nitazoxanide also can be considered when supportive care does not result in symptom resolution.
This patient has watery diarrhea associated with swimming pool exposure, and the oocysts observed microscopically represent Cryptosporidium. This parasitic protozoan is tolerant to chlorine and can persist for days in a chlorinated pool. Cryptosporidium has become the leading cause of swimming pool–related outbreaks of diarrheal illness. Swallowing infected water can result in infection. The incubation period is about 1 week, and the clinical presentation typically includes watery diarrhea, crampy abdominal pain, dehydration, fever, malaise, nausea, vomiting, and weight loss. The infection typically resolves in immunocompetent persons, but infection can be more serious and prolonged in those with immunocompromise, particularly in persons with AIDS who are not receiving combination antiretroviral therapy. Diagnosis can be established microscopically by visualization of oocysts with modified acid-fast staining. Because oocysts are shed intermittently, diagnosis may require stool antigen testing using polymerase chain reaction, enzyme immunoassay, or direct fluorescent antibody testing.