The chief executive of the UK Health Security Agency (UKHSA) today refused to be drawn on whether filthy water was to blame for the illness affecting at least 57 triathletes.

About 2,000 people took part in the UK leg of the World Triathlon Championship series in Sunderland at the end of July, which included a swim off the city's Roker beach.

The UKHSA said it would send those with symptoms a questionnaire and ask them to send a sample for testing to determine the cause of the illness.

Asked how difficult it would be to establish if there was E.coli in the water so long after the event, UKHSA chief executive Professor Dame Jenny Harries told BBC Radio 4's Today programme: "I think we need to be really careful in establishing the facts, in fact that's why the UK Health Security Agency's North East team are looking into this.

E-coli is a bacterial infection that can cause stomach pain and bloody diarrhoea and Environment Agency (EA) sampling nearby on 26 July detected 39 times the amount found during typical readings.

Professor Dame Jenny Harries said: "Predominantly, an event such as this is the responsibility of the organisers working with the Environment Agency but we have already worked with British Triathlon, who have been very proactive in sending out a questionnaire, which is critical for our work."

Asked if the possible E.coli could have been from sewage discharged into the sea, she said: "As I think both Northumbrian Water and the organisers British Triathlon have said, there are a number of different samples, different testing points and there will be samples from the individual athletes, and until we have all of that put together it's very important to think carefully about what associations are being made, none of that is available at the moment."

Australian triathlete Jake Birthwistle, who competed in the event, posted the Environment Agency's results on Instagram and said he had felt ill after the event.

He said: "Have been feeling pretty rubbish since the race, but I guess that's what you get when you swim in s***. The swim should have been cancelled."

Another athlete said: "That now explains why I spent Monday night with my head in the toilet after racing Sunday morning!"

The risk to the wider public is low, the UKHSA said in a statement.

Campaigners have long complained of sewage discharges along the stretch of coastline where the swim took place.

The EA said water off the beach was classed as excellent last year based on samples taken in the previous four summers.

British Triathlon, the governing body for UK triathlons, said its own testing results passed the required standards for the event.

It said on its website: "We are aware there are concerns around water quality results for a test taken on 26 July by the Environment Agency as part of their regular testing in the local area.

"These tests were taken outside of the Roker Pier arms and not in the body of water used for the swim and published on Monday 31 July following the event."

Northumbrian Water said there had been no sewage discharges at the beach since 2021.

An Environment Agency spokesperson said: "We routinely sample and monitor bathing waters, including at Roker, to provide information for bathers and support our ongoing work to improve their condition.

"The beaches at Roker and Seaburn were both classified as 'excellent' last year based on samples taken throughout the season from May to September over the last four years.

Read more:
Water firms apologise for sewage discharges and vow to spend £10bn cleaning up their act
'No end in sight' for sewage dumps as Environment Agency figures show year-on-year increase

"Temporary dips in water quality can be caused by several factors, including heavy rain.

"We will continue to investigate pollution sources and drive improvements to ensure cleaner and healthier waters for people to enjoy."

A Northumbrian Water spokesperson said: "We have had no discharges from any of our assets that might negatively impact water quality at either Roker or the neighbouring Whitburn North bathing water since October 2021.

"Both bathing waters were designated as 'excellent' in the latest Defra classifications and sampling to date in the current season indicate this high quality is being maintained."