Thousands of cases of cryptosporidiosis are reported in England each year, but health authorities say infection through drinking water is "very rare".
In May 2024, an outbreak in and around Brixham, Devon, resulted in more than 140 cases being confirmed, with four people requiring hospitalisation.
What is the cryptosporidium parasite and how dangerous is it?
Cryptosporidium is a tiny organism that causes illness in humans and some animals, health officials say.
According to the UK Health Safety Agency (UKHSA), the substance is found in human and animal faeces and can contaminate water bodies, swimming pools, raw milk and fresh food.
Anyone can become infected, and there is no effective drug treatment for cryptosporidiosis; the main symptom is prolonged diarrhea.
Professor Paul Hunter, a microbiologist and infectious disease specialist at the University of East Anglia, said most people recover within a couple of weeks, but for a small number of people with severely weakened immune systems it could be fatal.
He said most people would not need to see a doctor unless they were seriously ill or a child.
Where exactly in Devon was this substance found?
«"Small traces" of the parasite were found in tap water in and around Brixham, south Devon, during an outbreak in May 2024.
South West Water has issued an urgent boil water warning for around 40,000 residents after positive results were found in water samples.
The advisory against drinking tap water without boiling it first remained in place in some homes for 54 days before it was finally lifted on July 8, 2024.
In March 2026, South West Water admitted responsibility for supplying water that was unfit for drinking and issued a "full and unreserved apology".
On Tuesday, the company was fined £1.853 million after Judge Stuart Smith told the court it was a "major public health incident" that had "resulted in significant disruption to everyday life." He said the damage was "widespread and profound.".
How large was the outbreak?
There have been 143 confirmed cases of cryptosporidiosis linked to the Devon outbreak, but the true number of cases is likely to be "significantly higher," said Dr Beth Smout, acting regional deputy director of health protection at UKHSA.
«"We know that more people have shown symptoms, but not everyone has been tested, so the true scale of the problem is likely larger," she said.
«"This was a very serious outbreak, both in scale and in the impact on local residents, businesses and the wider community.".
Is drinking water the only source of disease outbreaks?
According to the latest available data, around 4,000 people in England will become ill with cryptosporidiosis in 2025.
«"Cryptosporidium outbreaks associated with drinking water are extremely rare," Smout said.
«"It's a parasite that's usually carried by animals, so infection mostly occurs through contact with farm animals, such as people visiting petting zoos," she added.
Hunter, who sits on the World Health Organization's committee on drinking-water quality, said outbreaks had become less frequent recently following new laws requiring British water companies to carry out more testing for cryptosporidia.
However, he noted that data on disease outbreaks is no longer published on a regular basis.
«"It's often difficult to determine how many outbreaks we're seeing," he said.
«"Drinking water isn't the only cause of disease outbreaks. We see outbreaks in swimming pools quite often, there have been outbreaks associated with unpasteurized milk, and we see outbreaks in daycare centers.".
«'Small traces' of the parasite were found in Brixham, south Devon, during an outbreak in May 2024 [BBC].
What should you do if Cryptosporidium is detected in your area?
During the 2024 Devon outbreak, thousands of residents were advised to boil water before using it for drinking, cooking, handling food or brushing teeth.
People are also advised to wash their hands thoroughly with soap and warm water before handling food, after using the toilet or handling animals, the UK Health Security Agency (UKHSA) said.
Cryptosporidiosis is a "highly contagious" disease, according to the guidelines, and those with symptoms should wash clothes at the highest temperature possible and avoid sharing towels.
People suffering from this condition should refrain from swimming for at least two weeks after the diarrhea stops.
What are the symptoms of cryptosporidium disease?
According to government guidelines, the main symptoms of cryptosporidiosis include:
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profuse watery diarrhea
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stomach ache
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nausea or vomiting
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subfebrile temperature
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loss of appetite, which can lead to dehydration and weight loss.
Health officials say the symptoms are similar to those of other stomach infections, and the only way to definitively confirm the illness is to send a stool sample to a lab for testing.
How to treat cryptosporidiosis?
According to the UKHSA, there is no specific treatment for cryptosporidiosis.
The guidelines say that most people with a healthy immune system recover within a month, adding that it is important to drink plenty of fluids, as diarrhea or vomiting can lead to dehydration, as well as the loss of important sugars and minerals from the body.
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The head of the water resources department was questioned by members of parliament regarding the cryptosporidia outbreak.
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At the meeting, representatives of the water supply company revealed «inconvenient truths.».
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An outbreak of aquatic parasites continues to spark public anger.
Related links
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UK Health Security Agency
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Southwest Water
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Torbay Council