Overview
Cryptosporidium is a microscopic parasite that infects the lining of the small intestine and causes cryptosporidiosis, a profuse, watery diarrhea. In people with healthy immune systems, illness can last up to about three weeks. In people with weakened immune systems, it can lead to life-threatening malnutrition and wasting.[1]
The parasite spreads through oocysts, tough-walled forms shed in stool. They are extremely tolerant to chlorine, which is why pools and water playgrounds were linked to more than half of U.S. outbreak cases from 2009 to 2017.[1] Globally, it is one of the most important causes of serious diarrhea in young children.[2]
Classification
- Phylum: Apicomplexa
- Family: Cryptosporidiidae
- Genus: Cryptosporidium
- Main human species: C. hominis and C. parvum
Cryptosporidium belongs to the Apicomplexa, the same group of single-celled parasites as the organisms that cause malaria and toxoplasmosis. C. hominis infects mainly humans, while C. parvum also infects cattle and other animals, which is why contact with calves is a recognized source of infection.
How Cryptosporidium Spreads
Transmission is fecal-oral: by swallowing contaminated recreational water, drinking water, or food, or through contact with infected people or animals.[1] Between 2009 and 2017, U.S. public health officials reported 444 cryptosporidiosis outbreaks involving 7,465 cases:[1]
| Outbreak source | Share of outbreaks | Share of cases |
|---|---|---|
| Treated recreational water (pools, water playgrounds) | 35.1% | 56.7% |
| Contact with cattle | 14.6% | — |
| Contact with infected people in child care | 12.8% | — |
The number of reported outbreaks rose by an average of about 13% per year over the period.[1]
The Milwaukee outbreak
In the spring of 1993, Milwaukee experienced a massive waterborne outbreak. Oocysts passed through the filtration system of one of the city's water-treatment plants, and the rate of Cryptosporidium detection in stool samples rose more than 100-fold. Investigators estimated that 403,000 people developed watery diarrhea. Among 285 people with laboratory-confirmed infection, 93% had watery diarrhea, 84% abdominal cramps, 57% fever, and 48% vomiting. The median illness lasted 9 days, with a range of 1 to 55 days.[3] Investigators concluded that the water-quality standards and patient testing of the time were not adequate to detect the outbreak.[3]
Global Burden
The Global Enteric Multicenter Study (GEMS) followed 9,439 children with moderate-to-severe diarrhea and 13,129 matched controls in Africa and Asia. Most attributable cases were caused by just four pathogens: rotavirus, Cryptosporidium, enterotoxigenic E. coli, and Shigella. In toddlers aged 12–23 months, Cryptosporidium infection was associated with a higher risk of death (hazard ratio 2.3).[2]
Cryptosporidiosis is increasingly recognized as an important cause of illness and death worldwide, and research has confirmed its role in both childhood diarrhea and childhood malnutrition.[4]
Diagnosis
Diagnosing Cryptosporidium requires specialized testing, and a routine stool ova-and-parasite exam may not look for it unless it is specifically requested. Conventional tests are often insensitive; antigen-detection tests and PCR improve sensitivity, though a 2015 review described multiplexed antigen and molecular tests as underused.[4] If you have prolonged watery diarrhea after swimming, animal contact, or travel, it is worth asking your clinician whether Cryptosporidium was tested for.
Treatment
- Hydration comes first. Most people with healthy immune systems recover on their own, and preventing dehydration is the most important step.
- Nitazoxanide. In a randomized, double-blind, placebo-controlled trial of 100 adults and children in Egypt, diarrhea had resolved by day 7 in 80% of patients given nitazoxanide versus 41% on placebo. The drug also shortened oocyst shedding.[5]
- Weakened immunity. Treatment has some effect in healthy hosts but no proven efficacy in people with AIDS, and new drugs and vaccines are still in development.[4]
Probiotics have not been established as a treatment for cryptosporidiosis. For supportive gut care during and after diarrheal illness, see our guide to probiotics for diarrhea.
Prevention
- Don't swim while you have diarrhea, and follow public health advice to stay out of pools for two weeks after diarrhea stops. Public health officials identify this as a key message for reversing the rise in outbreaks.[1]
- Keep children with diarrhea home from child care until they have recovered.[1]
- Wash hands with soap and water after contact with animals, especially calves, and after using the toilet or changing diapers. Alcohol-based sanitizers do not work well against Cryptosporidium.
- Avoid swallowing pool, lake, or river water, and be cautious with untreated water when traveling. See our page on travelers' diarrhea.
When to See a Clinician
See a clinician for diarrhea lasting more than a few days, signs of dehydration, blood in the stool, or high fever. People with weakened immune systems, including those with HIV, transplant recipients, and people receiving chemotherapy, should seek care promptly for any watery diarrhea. Infants, young children, older adults, and pregnant people are more vulnerable to dehydration.
This page is for educational purposes and is not medical advice. Consult a qualified healthcare provider about diarrheal illness and parasite testing.