The Department of Health is warning people who have had diarrhoea not to enter any swimming pool, water spray park or other aquatic facility for at least two weeks after they have made a full recovery.
The warning follows a significant increase in cryptosporidiosis cases in Western Australia, with most cases in metropolitan Perth.
In February 2025, an average of 70 cases a week were notified, which is well above the seasonal increase seen in summer in past years.
Cryptosporidiosis is a diarrhoeal disease due to a microscopic parasite Cryptosporidium that causes an infection of the gastrointestinal tract. It is easily spread from person-to-person in households, childcare facilities, and via swimming pools, waterparks, interactive fountains, and spas.
The most common symptoms include diarrhoea, stomach cramps and sometimes fever, nausea and vomiting.
Executive Director of Environmental Health Dr Michael Lindsay said that Cryptosporidium could easily spread to other people through water.
"An infected person can pass on cryptosporidiosis to other people if they don't wash their hands properly after going to the toilet. Waterborne transmission can happen when people accidentally swallow contaminated water while swimming in pools or other aquatic facilities," Dr Lindsay said.
"People may not realise they remain infectious for some time after diarrhoeal symptoms stop, so that's why we're asking people to avoid swimming for two weeks after their symptoms cease."
The parasite can survive for long periods in water and the environment and is not destroyed by regular chlorination. Aquatic facilities require proper water treatment procedures to maintain cleanliness, especially after any faecal incidents.
Currently, there is no evidence that any public swimming pools have faulty disinfection systems or are constantly infected. The Department is keeping a close eye on the situation.
"The Department's key priority is the prevention of further cases through alerting people about hygiene measures at pools and precautions to reduce the risk of spread in childcare facilities and household settings," Dr Lindsay said.
It could take up to 12 days after exposure for symptoms to develop, and individuals may be infectious from the onset of symptoms until two weeks after symptoms resolve.
There is no specific treatment for the infection and symptoms may last a few weeks in some people.
Certain groups are more at risk of severe illness if infected, including younger children, pregnant women and people with weakened immune systems.
Anyone concerned about their symptoms should contact their GP.
If you have diarrhoea, you should:
- wash your hands thoroughly for 15 seconds with soap and running water after using the toilet
- avoid swimming for at least two weeks after your symptoms resolve
- avoid sharing towels for at least two weeks after your symptoms resolve
- avoid preparing food for others for at least 48 hours after your symptoms resolve
- keep children who have diarrhoea home from preschool, childcare or playgroup until 48 hours after the diarrhoea has completely stopped.
To avoid catching cryptosporidiosis:
- wash your hands thoroughly for 15 seconds with soap and running water after using the toilet, changing nappies, and before preparing or handling food or drinks
- avoid swallowing or putting pool or spa water in your mouth
- ensure children who are not toilet-trained are wearing appropriate swimming nappies or waterproof tight-fitting pants over swimmers
- change nappies in a bathroom and not at the poolside – this will prevent germs being spread to surfaces or objects in and around the pool
- wash your child thoroughly (especially on the bottom) with soap and water before going swimming
- wash their hands with soap and water after changing a child's nappy.
