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This fact sheet answers frequently asked questions about cryptosporidiosis.

Cryptosporidiosis is an intestinal illness caused by a parasite called Cryptosporidium parvum.

The basics

What is cryptosporidiosis?

It was first recognized as a cause of human illness in 1976. In the spring of 1993 it gained national attention after approximately 400,000 people in Milwaukee became ill with diarrhea after drinking water contaminated with the parasite.

Who gets cryptosporidiosis?

Anyone can get a cryptosporidium infection. People at greatest risk for severe illness are those with weakened immune systems such as people with HIV infection, on chemotherapy or on high-dose steroid therapy after organ transplant.

Are there any restrictions for people with cryptosporidiosis?

Yes. Health care providers must legally report cases of cryptosporidiosis to the local board of health.

To protect the public, workers at food-related businesses who have cryptosporidiosis must stay out of work until they don’t have diarrhea and one lab test on a stool sample shows that there are no cryptosporidium germs. Workers in food-related businesses who have diarrhea and live with someone who has cryptosporidiosis must also show that they have no cryptosporidium in their stool. This regulation also includes workers in schools, residential programs, day-care and health care facilities who feed, give mouth care, or dispense medications to clients.​


What are the symptoms?

The most common symptom is watery diarrhea. Other symptoms include weight loss, stomach cramps, nausea, vomiting, headache, and mild fever. These symptoms generally appear within 2 to 14 days of swallowing the parasite. In otherwise healthy people, these symptoms usually go away on their own within 1 to 20 days (average 10). Some people might not have any symptoms. In people with weakened immune systems, symptoms are more severe, last longer and can lead to severe dehydration and even death.

How is cryptosporidiosis spread?

Infection occurs after swallowing the parasite. The parasite resides in the stool (feces) of infected people and animals, especially cattle. The disease can spread from one person to another if an infected person prepares food without thoroughly washing their hands.

The germs can also spread by drinking contaminated water. In rare cases, cryptosporidiosis can spread through lakes and swimming pools when people who have diarrhea swim in the water. The parasites can live in the water and infect other swimmers, particularly those who swallow the water.


How can I prevent cryptosporidiosis?

Take the following steps to minimize your chance of getting and spreading infection:

  • Always wash your hands after using the toilet, changing diapers, and before handling food
  • Wash your hands after contact with animals, especially cattle
  • Do not drink from streams, brooks, or lakes when hiking or camping
  • Only drink boiled water when traveling in developing countries or whenever you are unsure of the drinking water quality. Bring water to a rolling boil for one minute to eliminate cryptosporidium
  • Comply with any water advisories issued by local and state authorities. Massachusetts has a low likelihood that cryptosporidium would be a problem in public drinking water

People having problems with their immune system may have a more severe illness. If the parasite infects them, they may want to consider these additional recommendations:

  • Be particularly careful to avoid fecal contact (contact with stool)
  • Bring tap water to a rolling boil for one minute before drinking it or making ice cubes with it
  • Consider the use of a home water filtering system with a very fine filter (with an absolute pore size of 1 micron or smaller). Such filters include: reverse-osmosis filters; filters labeled as “absolute” 1 micron filters; and those labeled as meeting National Sanitation Foundation standard #53 for cyst removal. Use the home water filtering system according to manufacturers’ instructions
  • Note: You can use commercial bottled water, but it is not checked for cryptosporidium and is not guaranteed to be free of this parasite 
  • Avoid swallowing water when swimming. Lakes, streams, and swimming pools may contain cryptosporidium, and chlorination is not effective in eliminating the parasite


How is the disease diagnosed and treated?

Diagnosis happens by identifying the parasite in a stool sample. A limited number of medications are available to help treat the infection. In case of dehydration, a person will need fluid replacement. Consult your health care provider for more information.

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