Norovirus 'most likely' cause of illness after Sunderland triathlon events, investigators reveal

Norovirus is the 'most likely' cause of the vomiting and diarrhoea experienced by athletes taking part in the events in Sunderland during the World Triathlon Championship series in July, investigators have revealed.

Scores participants reported falling ill after the events at Sunderland's coast on July 29 and 30, 2023.

The UK Health Security Agency (UKHAS) North East launched an investigation working with British Triathlon and Sunderland City Council.

Preliminary findings announced today, Tuesday, August 15, reveal a total of 88 people who took part in the events have so far reported experiencing diarrhoea and/or vomiting symptoms after the event.

The agency said 31 samples have been received and tested for a range of viral and bacterial pathogens.

Laboratory results received so far indicate that 19 of the 31 people (60%) who sent faecal samples had evidence of Norovirus infection, the agency said, with the remaining samples either testing negative or were positive for other infections including sapovirus, astrovirus and rotavirus.

While UKHAS had urged people to 'think carefully about associations being made', there were concerns raised about the levels of E.Coli detected in water quality tests by the Environment Agency in the days before the triathlon events.

British Triathlon carried out water quality testing in the swim area for the triathlon in the two years leading up to the event, as well as in the build up to and over the race weekend, to ensure that water in the area where participants swam was safe.

However, an Environment Agency test on July 26, which was outside the swim zone, detected 39 times the amount of E.coli bacteria found in the water during typical readings.

But UKHSA said to date there have been no lab confirmed reports of micro-organisms, such as E coli O157/STEC (Shiga toxin-producing Escherichia coli), which may cause severe gastrointestinal illness. Although no STEC has been detected, laboratory results do show other E. coli present in four samples.

However, the agency stressed people can naturally carry organisms in their gut, and so it would not be possible to say whether they had a positive result due to their participation in the event or that they were already carrying these organisms.

Investigators said while it is not uncommon to detect more than one infection following testing of faecal samples, the predominance of Norovirus makes it the most likely explanation of illness in participants.

They said an in-depth survey of all participants who contacted the protection remains underway, and anyone who has not yet contacted British Triathlon to report symptoms is encouraged to do so.

Individuals are being updated on their lab results as and when they are available, and a fuller outbreak report will be made available once all investigations have been undertaken, the agency said.

It added Norovirus is very easily transmitted through contact with people with the infection and any food, water, surfaces or objects that have been contaminated with the virus.

Investigations are continuing, but UKHSA said the exact source of the infections may not be possible to determine. 

Dr Kirsty Foster, Consultant in Health Protection at UKHSA, said: “We thank everyone who took the time to contact British Triathlon to undertake sampling and respond to our epidemiological investigations and I hope that today’s preliminary findings will offer some reassurance.

“Norovirus is a very unpleasant stomach bug but tends to pass after a few days with most people usually making a complete recovery without any specific treatment. Rest and drinking lots of fluids are important to avoid dehydration.

"Norovirus can easily spread from person to person, particularly in large groups.

“The risk to the wider public remains very low. However it is always important that we all follow advice on how to manage symptoms of diarrhoea and vomiting and good hygiene is important to prevent others from becoming infected.

"This includes thorough handwashing, especially after toilet visits and before eating. Any contaminated surfaces should be thoroughly disinfected with a bleach-based cleaner after an episode of illness."

Dr Foster added: “Many people enjoy open swimming and the considerable social and wellbeing benefits it brings. However it is important to remember that anyone can become unwell from swimming in open water as there will always be micro-organisms present.

"There are a number of ways people can reduce their risk of illness though and these are detailed in the Swim Healthy guidelines.”

A spokesperson for Sunderland City Council said in a statement: "UKHSA's North East Health Protection team have identified Norovirus as the most likely cause in their preliminary findings into a number of participants reporting feeling unwell after the World Triathlon Championship Series event.

 "We are sorry to hear that a number of people have been unwell but we hope these findings reassure those who live in and visit our area that our award-winning blue flag beaches are safe to swim from and are there to be enjoyed by all, during the summer months and beyond.

"British Triathlon carried out water quality testing in the swim area in the two years leading up to the World Triathlon Series event, as well as in the build-up to and over the race weekend, to ensure that water in the area where participants swam was safe to do so.  Test results passed the required guidelines for hosting a World Triathlon Championship Series event."

A spokesperson for British Triathlon said: "British Triathlon welcomes this interim report from the UK Health Security Agency (UKHSA) and its findings, and we are very grateful to everyone who has cooperated with the investigation.

"British Triathlon is committed to supporting the investigation and encourages anyone affected to make contact."

• Information and health advice on swimming in open water is available here: https://www.gov.uk/government/publications/swim-healthy-leaflet/swim-healthy. 
• Information on Norovirus is available here: https://www.nhs.uk/conditions/norovirus/