Skip to main content


Cryptosporidiosis is a disease caused by the parasite cryptosporidium (usually Cryptosporidium parvum and Cryptosporidium hominis).


The most common symptom is watery diarrhoea, which can range from mild to severe.

Anybody can become infected with cryptosporidium, although it is most common in children aged 1-5 years. Most healthy people recover without treatment within a month but it can cause severe illness in people with weak immune systems.


The cryptosporidium parasites can be found in water, food, soil or on surfaces or dirty hands that have been contaminated with the poo of animals or people infected with the parasite. 

The parasites are resistant to chlorine. Outbreaks of cryptosporidiosis have been linked to drinking or swimming in contaminated water and contact with infected lambs and calves during visits to open farms.

​Public Health Wales provides advice on controlling outbreaks of cryptosporidiosis and monitors any outbreak to find the source of the infection. The Cryptosporidium Reference Unit (CRU) is based at Public Health Wales Microbiology Swansea.


​If you are a member of the public and need advice, please contact NHS Direct Wales or your GP.