Cryptosporidiosis, often called 'crypto', is an intestinal infection caused by the microscopic parasite Cryptosporidium. Cryptosporidiosis occurs worldwide and is a common cause of acute diarrhoea in young children. As well as infecting humans, Cryptosporidium parvum occurs in a variety of animals including cattle, sheep, dogs and cats. In people with normal immune systems the disease is generally not serious. Cryptosporidium hominis also causes infection in humans. However, people with weakened immune systems (e.g. some people receiving cancer treatment, people on steroid therapy and people with HIV/AIDS) may develop severe and long lasting illness. The disease tends to be more common during the warmer months.

Community outbreaks of cryptosporidiosis have been attributed to contaminated water supplies, recreational water supplies (swimming pools) and child/day care centres.

Signs and Symptoms: 

The most common symptom is diarrhoea, which is usually watery and may be profuse. The diarrhea is associated with cramping abdominal pain. Other symptoms include nausea, vomiting, fever, headache, and loss of appetite. Some people infected with Cryptosporidium may not develop any symptoms.

In healthy young children the illness resolves without specific treatment and lasts only a few days. In people with normal immune systems the symptoms often fluctuate but recovery is expected in less than 30 days. People with weakened immune systems may not clear the parasite and the illness may persist.


There is no specific treatment for cryptosporidiosis. Maintenance of an adequate fluid intake is the most important consideration for people with crypto, especially over the summer months when crypto is more common. Persons with severe illness, difficulty in maintaining and adequate fluid intake or long lasting diarrhoea should seek medical advice.


Cryptosporidium is shed in the faeces of infected humans and animals from the onset of symptoms and may continue to be shed in the faeces for several weeks after symptoms have resolved. The infectious agent is a hardy, thick-walled cyst called an "oocyst". The oocyst can survive in a moist environment for up to 6 months. It may then be transferred to humans when people accidentally swallow the parasite, in one of several ways:

  • person-to-person spread, especially in households and child care settings
  • handling of infected pets, farm animals, or their faeces
  • food and water contaminated by the faeces of infected animals or persons. This includes swallowing contaminated recreational water, for example in swimming pools and dams
  • exposure to faeces during sexual activities.

Cryptosporidium is resistant to the usual levels of chlorine in swimming pools and may survive for days in pools. High doses of chlorine and cleaning of filters can remove Cryptosporidium from a contaminated pool. Oocysts are sensitive to hydrogen peroxide, ozone and ultraviolet radiation.

The time from contact with the parasite to development of illness is usually about 7 days, but can be longer.

Practicing good personal hygiene can reduce the potential for contracting cryptosporidiosis.

Ongoing management: 

Children with diarrhoea should not return to child care or school until diarrhoea has ceased for 24 hours. Food handlers and health care workers should remain away from work until two days after diarrhoea has ceased.

As people with cryptosporidiosis can remain infectious even after symptoms have settled, they should not go swimming while they have diarrhoea and for two weeks after diarrhoea has stopped.


There is no vaccine to prevent cryptosporidiosis and no way of preventing the illness in people who have been exposed.

There are numerous ways to prevent exposure to crypto, including:

  • washing hands thoroughly after using the toilet, changing nappies and before handling food or eating
  • washing the hands of toddlers and babies after a nappy change
  • washing hands after contact with pets, and after cleaning up animal faeces
  • washing hands after gardening or other direct contact with soil
  • washing hands after contact with cattle and other farm animals
  • washing fruit and vegetables before eating them
  • not eating or drinking unpasteurized milk products
  • not drinking untreated water and inadequately filtered water and boiling untreated water or water of unknown quality for a t least one minute before drinking
  • not swallowing water in swimming pools or other recreational water
  • avoid swimming in natural waters (rivers, creeks, dams, surf) within a week after heavy rain
  • not sharing linen and towels during diarrhoea and for 2 weeks after diarrhoea has stopped.

People with weakened immune systems may need to take special precautions to reduce their risk.

Help and assistance: 

For further information, please contact your local doctor, health centre or nearest public health unit; or call 13 HEALTH (13 43 25 84) 24 hours a day 7 days a week for the cost of a local call.

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Diarrhoea in young children - fact sheet