Cryptosporidium parasites are protected by a thick coating that allows them to survive in chlorinated pool water.
Cryptosporidium, also known as Crypto, are small parasites that live in water and enter the body through food or drinks.
They cause a disease called cryptosporidiosis, the most common symptom of which is watery diarrhea. It can also cause nausea, vomiting and fever.
Symptoms usually last about two weeks, but can last longer. Young children and people with weak immune systems are more likely to be affected more severely.
Parasites are protected by a thick outer layer that allows them to survive outside the body. In cool, humid conditions, they can live for several months.
They are also resistant to chlorine, so they can live in pools for up to a week.
Ingesting just 10 Cryptosporidium parasites is enough to make you sick
Outbreaks of cryptosporidiosis have been linked to drinking or swimming in contaminated water. Foods prepared with contaminated water, such as salads that are washed with it, can also be a danger.
Farmers who handle livestock may also be at risk, as the infection can be contracted from cows, goats and sheep, especially lambs.
Once swallowed, the Cryptosporidium shells split open and the parasites are released.
However, some of the parasites will pass through a person’s digestive system intact, so infection can occur by ingesting excrement particles from an infected person, such as when changing the diapers of a sick baby.
Infected people can eliminate up to 100 million parasites in a single bowel movement. Swallowing just ten is enough to make you sick.
The UK Health Security Agency (UKHSA) provides advice on controlling cryptosporidiosis outbreaks and monitors outbreaks to find the source.