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Cryptosporidium Antigen, Feces

Cryptosporidiosis is a gastrointestinal illness caused by protozoa of the genus Cryptosporidium. Cryptosporidium is an extremely chlorine-tolerant intracellular protozoan parasite that causes waterborne outbreaks of diarrheal illness worldwide. An estimated 748,000 cryptosporidiosis cases occur annually in the United States.

Infection results from the ingestion of oocysts through fecally contaminated food or water, or through contact with an infected person or animal. Ingestion of fewer than 10 oocysts can cause infection in healthy individuals. Infected individuals can excrete ooxysts for up to 60 days after resolution of gastrointestinal symptoms.

Cryptosporidium oocysts are extremely chlorine tolerant and can survive for up to 10 days in chlorinated water. This tolerance makes Cryptosporidium ideally suited for transmission via recreational and drinking water.

The majority of cases of cryptosporidiosis in humans are caused by C. hominis and C. parvum. C. hominis is mainly spread through human-to-human transmission, whereas C. parvum can be spread through human-to-human or animal-to-human transmission. Human infections caused by C. meleagridis, C. canis, C. felis, C. ubiquitum, C. cuniculus, C. suis, and C. muris have been reported.

Risk factors for cryptosporidiosis include ingestion of recreational water, ingestion of untreated drinking water, contact with livestock, recent international travel or contact with infected persons.

Groups at particular risk of infection include the immunocompromised, especially those with HIV infection, family members and sexual partners of infected patients, children and caretakers in day care centers, animal handlers and travelers.

Cryptosporidiosis is typically characterized by profuse, watery, nonbloody diarrhea. Other symptoms can include weight loss, abdominal pain, anorexia, fatigue, cramps, headache, fever, and vomiting. Asymptomatic infection also can occur. Recurrence of symptoms after apparent resolution is common. The disease is self-limiting and symptoms typically resolve within 2 to 3 weeks in immunocompetent persons. Cryptosporidiosis can be treated by nitazoxanide.

Health-care providers should consider cryptosporidiosis in their differential diagnosis when a patient experiences diarrhea lasting more than 3 days. Microscopic examination of stool for ova and parasites is not very sensitive because oocyst excretion is intermittent. Three stool specimens collected on separate days should be examined before considering test results to be negative.

Commercially available rapid antigen detection immunoassay kits are more sensitive and specific than microscopic examination. Sensitivity is 95% sensitivity and specificity is 98%. Specimen requirement is 10 g of a random stool sample submitted in a screw-capped, plastic container with 10 % formalin.

Cryptosporidium is also included in the FilmArray Gastrointestinal Panel that tests for 22 common pathogens. Specimen requirement is a fresh diarrheal stool sample from inpatients or a stool sample submitted in Cary-Blair transport media for outpatients. 

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