Among the many protozoan parasites in the genus Cryptosporidium, Cryptosporidium hominis and C. parvum most frequently cause human infections.
Cryptosporidium is transmitted via the fecal-oral route. Its low infectious dose, prolonged survival in moist environments, protracted communicability, and extreme chlorine tolerance make Cryptosporidium ideally suited for transmission through contaminated drinking or recreational water, such as swimming pools. Transmission can also occur through contaminated food, or contact with infected people, or contaminated surfaces.
Cryptosporidiosis is endemic worldwide. Of 22 US Peace Corps volunteers, 9 developed anti-Cryptosporidium IgG while serving in Africa. International travel is a risk factor for sporadic cryptosporidiosis in the United States and other industrialized nations; however, few studies have assessed the prevalence of cryptosporidiosis in travelers. One study found 2.9% prevalence of Cryptosporidium infection among those with travel-associated diarrhea; cryptosporidiosis was significantly associated with travel to Asia, particularly India, and Latin America. Another study found a 6.4% prevalence of Cryptosporidium infection among North Americans with diarrhea associated with travel to 2 Mexican cities. This study suggests an association between cryptosporidiosis and length of travel.
Symptoms begin within 2 weeks (typically 5–7 days) after infection and are generally self-limited. The most common symptom is watery diarrhea. Other symptoms can include urgency, tenesmus, abdominal cramps, flatulence, nausea, vomiting, weight loss, fever, decreased appetite, fatigue, joint pain, and headache. In immunocompetent people, symptoms typically resolve within 2–3 weeks; patients might experience a recurrence of symptoms after a brief period of recovery before complete symptom resolution. Clinical presentation of cryptosporidiosis in HIV-infected patients varies with level of immunosuppression, ranging from no symptoms or transient disease to relapsing or chronic diarrhea or even choleralike diarrhea, which can lead to life-threatening wasting and malabsorption. Extraintestinal cryptosporidiosis (in the biliary or respiratory tract or rarely the pancreas) has been documented in children and immunocompromised people.
Tests for Cryptosporidium are typically not included in routine ova and parasite testing. Therefore, clinicians should specifically request testing for this parasite, when suspected. Because Cryptosporidium can be excreted intermittently, multiple stool collections (3 stool specimens collected on separate days) increase test sensitivity. Diagnostic techniques include direct fluorescent antibody (considered the gold standard), EIA testing, rapid immunochromatographic cartridge assays, and microscopy with modified acid-fast staining. False-positive results might occur when using rapid immunochromatographic cartridge assays if they are not used according to the manufacturer’s directions. Confirmation by microscopy might be considered.
Most immunocompetent people will recover without treatment. Nitazoxanide is approved to treat cryptosporidiosis in immunocompetent people aged ≥1 year. Nitazoxanide has not been shown to be an effective treatment of cryptosporidiosis in HIV-infected patients. However, dramatic clinical and parasitologic responses have been reported in these patients after the immune system has been reconstituted with active combination antiretroviral therapy. Protease inhibitors might have direct anti-Cryptosporidium activity.
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