CDC Yellow Book 2024

Travel-Associated Infections & Diseases

Author(s): Michele Hlavsa, Dawn Roellig

INFECTIOUS AGENT: Cryptosporidium spp.




Children aged 1–4 years and their caregivers


Follow safe food and water precautions

Minimize fecal–oral exposures during sexual activity

Practice good hand hygiene


A clinical laboratory certified in moderate complexity testing; or contact CDC’s Waterborne Disease Prevention Branch ( for clinical and diagnostic questions (does not conduct cryptosporidiosis diagnostic testing)

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 (e.g., swimming pools). Transmission also can occur through contact with fecally contaminated surfaces, by eating contaminated food, or through contact with infected animals (particularly pre-weaned bovine calves) or people (e.g., when providing direct care, during oral–anal sex).


Cryptosporidiosis is endemic worldwide; the highest rates are found in low- and middle-income countries. An estimated 823,000 cryptosporidiosis cases occur in the United States each year, of which 9.9% are thought be due to international travel. The highest US rates of reported cryptosporidiosis are in young children aged 1–4 years and in people aged 15–44 years, particularly females (likely caregivers changing diapers and helping with toileting). International travel is a risk factor for sporadic cryptosporidiosis in the United States (population attributable risk is 11%) and other high-income nations; few studies, however, have assessed the prevalence of cryptosporidiosis in travelers.

One report identified a 6% prevalence of Cryptosporidium infection in North American travelers to Mexico; among travelers to Cuernavaca or Guadalajara who experienced travelers’ diarrhea, longer visits were associated with an increased risk for Cryptosporidium infection compared with bacterial diarrhea. Approximately 30% of patients with cryptosporidiosis in New York City reported international travel during their incubation period, particularly among those aged <20 years.

Clinical Presentation

Symptoms—most commonly, frequent, non-bloody, watery diarrhea—begin ≤2 weeks (typically 5–7 days) after infection and are generally self-limited. Other symptoms include abdominal pain, flatulence and urgency, nausea, vomiting, and low-grade fever. In immunocompetent people, symptoms typically resolve within 2–3 weeks, although patients might experience a recurrence of symptoms after a brief period of recovery and before complete symptom resolution.

Clinical presentation in immunocompromised patients varies with the level of immunosuppression, ranging from no symptoms or transient disease to relapsing or chronic diarrhea or even cholera-like 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 people.


Routine testing for ova and parasites does not typically include Cryptosporidium; specifically request testing for this organism when Cryptosporidium infection is suspected. New molecular enteric panel assays generally include Cryptosporidium as a target pathogen. Because Cryptosporidium is intermittently excreted in the stool, collect multiple samples (i.e., collect specimens on 3 separate days) to increase test sensitivity.

Other diagnostic techniques include microscopy with direct fluorescent antibody (considered the gold standard), enzyme immunoassay kits, molecular assays, microscopy with modified acid-fast staining, and rapid immunochromatographic cartridge assays. Note that rapid immunochromatographic cartridge assays can generate false-positive results; consider confirmation with microscopy. The Centers for Disease Control and Prevention (CDC)’s Waterborne Disease Prevention Branch ( can answer clinical and diagnostic questions but does not conduct cryptosporidiosis diagnostic testing. Health care professionals should contact their usual diagnostic laboratory for testing.

Infections caused by different Cryptosporidium species and subtypes can differ clinically. Most Cryptosporidium species, all with multiple subtypes, are indistinguishable by traditional diagnostic tests, however. To clarify cryptosporidiosis epidemiology and track infection sources, then, CDC coordinates CryptoNet, which provides Cryptosporidium genotyping and subtyping services in collaboration with state public health agencies. CryptoNet recommends against using formalin to preserve stool for Cryptosporidium testing, because formalin impedes reliable genotyping and subtyping.

Cryptosporidiosis is a nationally notifiable disease in the United States.


Most immunocompetent people recover from cryptosporidiosis without treatment; diarrhea can be managed by maintaining an adequate oral fluid intake. The US Food and Drug Administration has approved nitazoxanide as treatment for immunocompetent people aged ≥1 year with cryptosporidiosis.

Nitazoxanide has not been shown to be effective in immunocompromised patients. Instead, reconstitution of the immune system can result in robust clinical improvement in the absence of specific treatment. Protease inhibitors might have anti-Cryptosporidium activity. All patients (immunocompromised and immunocompetent) might need rehydration and electrolyte replacement.


Travelers can reduce their risk for cryptosporidiosis by carefully adhering to food and water precautions (see Sec. 2, Ch. 8, Food & Water Precautions) and using proper handwashing techniques (see Prevention & Control). Alcohol-based hand sanitizers are not effective against this parasite.

Travelers can also decrease the risk for infection by filtering drinking water with an absolute 1-µm filter or heating drinking water to a rolling boil for 1 minute (see Sec. 2, Ch. 9, Water Disinfection, and Drinking Water Treatment and Sanitation for Backcountry and Travel Use). Cryptosporidium oocysts are extremely tolerant of halogens (e.g., chlorine, iodine), so CDC recommends filtering or boiling water in high-risk areas.

To protect themselves, swimmers should avoid ingesting recreational water. To protect others, people infected with cryptosporidiosis 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.

Practicing safer sex (i.e., reducing contact with feces) can also decrease risk for infection.

CDC website:

The following authors contributed to the previous version of this chapter: Michele C. Hlavsa, Dawn M. Roellig

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