Among the many protozoan parasites in the genus Cryptosporidium, Cryptosporidium hominis and C. parvum cause >90% of 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 drinking or recreational water (such as swimming pools) that has been contaminated with Cryptosporidium. Transmission can also occur through eating contaminated food, contact with infected people (for example, while providing care or during oral-anal sex) or animals, or contact with fecally contaminated surfaces.
Cryptosporidiosis is endemic worldwide, and the highest rates are in developing countries. 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 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 longer length of stay.
Symptoms begin within 2 weeks (typically 5–7 days) after infection and are generally self-limited. The most common symptom is profuse, watery diarrhea. Other symptoms can include abdominal pain, flatulence, urgency, nausea, vomiting, and low-grade fever. In immunocompetent people, symptoms typically resolve within 2–3 weeks; patients might experience a recurrence of symptoms after a brief period of recovery and before complete symptom resolution. Clinical presentation of cryptosporidiosis in immunocompromised 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 dehydration and 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 Cryptosporidium infection is suspected. New molecular enteric panel assays generally include Cryptosporidium as a target pathogen. Because Cryptosporidium can be excreted intermittently, multiple stool collections (3 stool specimens collected on separate days) increase test sensitivity. Diagnostic techniques include microscopy with direct fluorescent antibody (considered the gold standard), EIA kits, 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.
Infections caused by the different Cryptosporidium species and subtypes can differ clinically. However, most Cryptosporidium species, all with multiple subtypes, are indistinguishable by traditional diagnostic tests. To better understand cryptosporidiosis epidemiology and track infection sources, CDC has launched CryptoNet (www.cdc.gov/parasites/crypto/cryptonet.html), which provides Cryptosporidium genotyping and subtyping services in collaboration with state public health agencies. CryptoNet recommends not preserving stool for Cryptosporidium testing in formalin because formalin impedes reliable genotyping and subtyping. Cryptosporidiosis is a nationally notifiable disease.
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 immunocompromised patients. However, dramatic clinical and parasitologic responses without specific treatment have been reported in these patients after the immune system has been reconstituted. Protease inhibitors might have direct anti-Cryptosporidium activity. Oral rehydration is the most effective supportive therapy in both immunocompetent and immunocompromised patients.
Food and water precautions (see Chapter 2, Food & Water Precautions) and handwashing (www.cdc.gov/handwashing). Cryptosporidium is extremely tolerant to halogens (such as chlorine or iodine). Water can be treated effectively by filtering with an absolute 1-µm filter or heating to a rolling boil (any water brought to a boil should be adequately disinfected; however, if fuel supplies are adequate, travelers may wish to boil for 1 minute to allow for a margin of safety). Alcohol-based hand sanitizers are not effective against the parasite.
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