Chlorine-resistant gastro parasites causing concern at public pools

The Victorian Department of Health warned the "highest number of reported cases for this season" were recorded in mid-March with 87 people reporting the infection.

"This year there has been 607 reported cases, over 600 per cent higher than the 84 cases notified in the same period in 2023. Many cases are linked to swimming in public pools," a Victorian health advisory said on March 20.

Cases of crypto infections have spiked since September 2023, the department said.

Pools in Melbourne, including Northcote Aquatic and Recreation Centre and Brunswick Baths, shut their doors temporarily in 2024 due to infections.

The communicable illness is a type of gastroenteritis caused by the parasite cryptosporidium. The parasite is highly resistant to the levels of chlorine found in public pools.

Crypto infections are transmitted via the faecal-oral route with the parasites entering through the mouth.

"This can happen directly through eating contaminated food and water or, more commonly, from person to person or animal to person," the advisory said.

"Swimmers can become infected when they accidentally swallow pool water contaminated with the parasite."

People with a crypto infection or an unknown cause of diarrhea are urged not to swim to avoid further pool contamination and the transmission of parasites.

Victoria's Department of Health said the most common symptoms of crypto are watery diarrhea and stomach cramps "which may last several weeks".

"It can be spread to others both during the illness, and for up to two weeks after symptoms resolve."

Other infection symptoms include fever, nausea, vomiting, bloating and a loss of appetite.

Some people who are infected may not show any symptoms.