Cryptosporidia are small apicomplexan protozoan parasites that infect the intestinal tract of humans and animals. They were conventionally categorized as coccidia, but are now known to be more closely related to the gregarines. Many species may infect humans, with the most common being Cryptosporidium hominis and C parvum. Infected humans and animals shed small (4-6 micrometer in diameter) infectious oocysts in their stool, and these can subsequently contaminate and survive in recreational and drinking water supplies.
Infection of humans occurs by the fecal-oral route or via ingestion of contaminated water or food. Infection is easily acquired, with an infectious dose of approximately 100 oocysts. Waterborne transmission is a primary mode of transmission and is commonly responsible for human outbreaks. This is due to the fact that Cryptosporidium species oocysts are resistant to cold temperatures and chlorine, and require extensive filtration or water treatment to remove them from drinking water.
The incubation period is typically 7 to 10 days following exposure. While most patients have symptoms, approximately 30% of infected individuals are asymptomatic. When symptoms are present, they usually include profuse watery diarrhea, malaise, anorexia, nausea, crampy abdominal pain, and low grade fever. Infection is usually self-limited in immunocompetent individuals, with resolution of symptoms in 10 to 14 days. However, diarrhea can be prolonged and life-threatening in immunocompromised patients such as those with AIDS, infants, and the elderly, and result in severe dehydration and wasting.
The fecal ova and parasite examination is an insensitive method for detecting Cryptosporidium, given the small size of the oocysts and their lack of trichrome staining. Instead, use of the Cryptosporidium antigen test (CRYPS / Cryptosporidium Antigen, Feces) or the multiplex gastrointestinal PCR panel (GIP / Gastrointestinal Pathogen Panel, PCR, Feces) is recommended for sensitive and specific detection. The antigen test is ideal for situations in which cryptosporidiosis is highly suspected (eg outbreak scenarios), whereas the PCR panel allows for simultaneous detection of multiple parasitic, viral, and bacterial causes of diarrhea.