Infectious Agent

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 contaminated drinking or recreational water (such as swimming pools). Transmission can also occur through eating contaminated food, through contact with infected animals (particularly preweaned bovine calves) or people (for example, when providing direct care or during oral-anal sex), or through contact with fecally contaminated surfaces.


Cryptosporidiosis is endemic worldwide, and the highest rates are found 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 a 3% prevalence of Cryptosporidium infection among those with travelers’ diarrhea; cryptosporidiosis was associated with travel to Latin America and to Asia, India in particular.

Another report identified a 6% prevalence of Cryptosporidium infection among North American travelers to Mexico. The authors of this study reported associations between duration of stay (longer visits associated with an increased risk of Cryptosporidium vs. bacterial diarrhea) and specific destination (travel to 2 cities in Mexico, in particular, increased the likelihood of Cryptosporidium infection).

Clinical Presentation

Symptoms (most commonly, profuse, watery diarrhea) begin within 2 weeks (typically 5–7 days) after infection and are generally self-limited. 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 may 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 and rarely the pancreas) has been documented in children and immunocompromised hosts.


Routine ova and parasite testing does not typically include Cryptosporidium ; clinicians should specifically request testing for this organism when Cryptosporidium infection is suspected. New molecular enteric panel assays generally include Cryptosporidium as a target pathogen. Intermittent excretion of Cryptosporidium in the stool necessitates collection of multiple samples (specimens collected on 3 separate days) to increase test sensitivity.

Other diagnostic techniques include microscopy with direct fluorescent antibody (DFA; considered the gold standard), enzyme immunoassay (EIA) kits, molecular assays, microscopy with modified acid-fast staining, and rapid immunochromatographic cartridge assays. Rapid immunochromatographic cartridge assays can generate false-positive results’; consider confirmation microscopy for specimens identified as positive by this method.

Infections caused by the different Cryptosporidium species and subtypes can differ clinically. However, despite all the variations in clinical presentation caused by this protozoan, 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 (, which provides Cryptosporidium genotyping and subtyping services in collaboration with state public health agencies. CryptoNet recommends not using formalin to preserve stool for Cryptosporidium testing because formalin impedes reliable genotyping and subtyping. Cryptosporidiosis is a nationally notifiable disease.


Most immunocompetent people recover without treatment. The US Food and Drug Administration has approved nitazoxanide as a treatment for 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 following reconstitution of the immune system. Protease inhibitors might have direct anti-Cryptosporidium activity. Oral rehydration is the most effective supportive therapy in both immunocompetent and immunocompromised patients.


Careful adherence to food and water precautions (see Chapter 2, Food & Water Precautions) and proper handwashing techniques ( can decrease the risk of infection. Alcohol-based hand sanitizers are not effective against the parasite. Treat water for drinking by filtering with an absolute 1-µm filter or heating to a rolling boil for 1 minute. Cryptosporidium is extremely tolerant of halogens (such as chlorine or iodine). To protect themselves, swimmers should avoid ingestion of recreational water. To protect others, cryptosporidiosis patients should not enter recreational water while ill with diarrhea and for the first 2 weeks after symptoms have completely resolved because of prolonged excretion of infectious oocysts.

CDC website:


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Michele C. Hlavsa, Dawn M. Roellig