Outbreaks of cryptosporidium linked to drinking water are, thankfully, very rare. It's probably a once-in-a-decade event. So, when one began to emerge in Brixham in 2024, it presented us with a genuinely unusual and significant challenge - one that tested our surveillance systems, our partnerships, and our ability to act quickly under pressure.
Here Beth Smout, Interim Regional Deputy Director of Health Protection for the South West, and Sarah Bird, Lead Consultant in Health Protection describes how we worked against those challenges.
What is cryptosporidium?
Cryptosporidium is a parasite, and it causes an unpleasant illness. Most people experience severe watery diarrhoea, but fever, stomach cramps and vomiting are also common, and symptoms can last for days or even weeks. For most people, the infection is self-limiting - it will pass in time - but for those with weaker immune systems it can be severe and prolonged. In this outbreak, a small number of people ended up in hospital.
We see around 4,000 cases of cryptosporidium across England each year. Outbreaks tend to be linked to contact with farm animals - a visit to a petting farm is a classic route of infection - or to activities like swimming. Contamination of a drinking water supply is far less common, which is part of what made Brixham so significant.
Spotting that something was wrong
We became aware of cases in the Brixham area through our normal surveillance channels. In any outbreak investigation of gastrointestinal illness, one of the first things we do is work with environmental health colleagues to conduct detailed questionnaires with those who have fallen ill. Typically, you'd expect a pattern to emerge - perhaps everyone visited the same location, or attended the same event. What we were seeing in Brixham was different. There was no single obvious setting that all the cases had in common.
At the same time, we started receiving calls from local GPs. They were concerned. They were seeing an unusually high number of patients presenting with diarrhoea and vomiting, and they had a sense that something was going on. And then there was social media. Members of the public were sharing their experiences online, and the volume and pattern of what they were describing added to our picture.
It was the combination of all three - laboratory-confirmed cases, worried GPs with local knowledge, and the noise from the public on social media - that gave us the early warning signal we needed. We could see quickly that this was something unusual and that we needed to act.
The response
Once we declared an outbreak, we brought together a multi-agency team drawn from a range of organisations including Torbay Council, Devon County Council, South Hams District Council, the NHS and South West Water to deliver the response and put control measures in place. The most visible of these was the boil water notice issued by South West Water. Initially, this applied to 17,000 properties, advising residents to boil water before drinking it, using it to brush their teeth, or preparing food with it. As investigators narrowed down the likely source of the contamination, the notice was scaled back to cover around 2,500 properties.
A boil water notice on that scale has a significant impact - not just on residents, but on businesses, schools and care homes. We worked to provide clear advice to all of those affected about how to continue operating safely. And for anyone experiencing symptoms, the guidance was clear: stay off work or school until symptoms had been fully resolved for at least 48 hours, to reduce the risk of passing the infection to others.
In total, 143 confirmed cases were associated with this outbreak, of which 126 were genetically linked to it. But we know the true number is likely to be substantially higher - many people with symptoms did not get tested as testing is only recommended for people with severe or prolonged diarrhoea, lasting for 7 days or more.
What we learned
Following the outbreak, Field Services at UKHSA conducted a research study surveying residents and visitors to the affected area. Around 850 people responded, sharing information about their symptoms, their behaviour before and after the boil water notice, and the wider impacts of the outbreak on their daily lives – including days off work or days off school. The full results will be published in the coming months.
Looking back, I think this outbreak demonstrated 2 things very clearly. First, the strong relationships that UKHSA Health Protection Teams have with partners, built up over time, outside of any incident. When something like this happens, you need to be able to move quickly, and that is so much easier when those relationships are already established.
Second, it showed just how vital early warning systems are. The combination of notified cases, GP intelligence and public reporting on social media came together to help us detect what was happening and respond rapidly. That early action matters enormously when you are trying to limit the spread of an outbreak and protect people's health.