Cryptosporidium Fact Sheet

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Cryptosporidium is a parasite that causes diarrhea

Cryptosporidium infections (cryptosporidiosis) have been reported in humans and a wide variety of animals such as cattle, dogs, and cats.  Infected humans and animals shed the parasite in their feces (stool).  As a result, Cryptosporidium can be found in environments contaminated by the feces of infected humans or animals.  Lakes, rivers, reservoirs, and shallow wells may be affected.  The parasite is highly resistant to chlorine, which is commonly used as a disinfectant in water treatment plants and recreational water venues, such as swimming pools and water parks.

Transmission can occur by coming into direct or indirect contact with feces of infected humans or animals, including:

  • Consumption of contaminated water or food
  • Swallowing contaminated water while swimming or soaking in a hot tub
  • Person-to-person contact, particularly in child care settings
  • Contact with objects contaminated with the feces of an infected person or animal
  • Handling infected pets or farm animals, most commonly affected are calves 
  • Sexual activity that involves contact with feces

Symptoms appear 1 to 12 days or more, after exposure, on average 7 days.

The most common symptoms are diarrhea and stomach cramps.  Fever, vomiting, and nausea may occur. Some infected people have no symptoms.  People with normal immune systems usually have symptoms for one to two weeks and then recover fully.  However, people with weakened immune systems, such as cancer patients, organ transplant recipients, and HIV-infected persons, may have more severe diarrhea that can persist long enough to become life-threatening.


Replacement of fluid lost through diarrhea may be necessary. Sometimes, treatment with medication is also necessary.  Patients with severe or long-lasting diarrhea should consult their health care provider.

Tests are available to look for Cryptosporidium in feces and in water

The Environmental Protection Agency (EPA) requires that certain large water companies routinely test water for Cryptosporidium.  Health care providers can do tests to help determine if a person is infected with Cryptosporidium.

Cryptosporidiosis can be prevented

  • Avoid drinking untreated water from lakes, streams, springs, or other sources.
  •  Boil any water of unknown quality for at least one minute before consumption (including water used in drinks and to make ice).  Using certain filters with a very small pore size (£ 1 micron) is also effective at reducing risk.
  • Avoid any direct contact with human or animal feces.
  • Wash hands after using the toilet, changing diapers, and before handling food or eating.
  • Wash hands after contact with or cleaning up after pets.
  • Wash hands after gardening or other direct contact with the soil.
  • Wash fruits and vegetables before eating them.
  • Avoid unpasteurized milk products.
  • Avoid swallowing water during swimming, even in public swimming pools.
  • Avoid swimming for two weeks after diarrhea stops, if infected with Cryptosporidium.

People with weakened immune systems may want to take extra action to reduce the risk:

  • Use boiled water, use certain filters, or use bottled water processed using a method that eliminates Cryptosporidium for all drinking water, including for tooth brushing.
  • Check with a health care provider for any other control measures to avoid cryptosporidiosis if you have a weakened immune system.