Experts: Olympic marathon swimmers likely to have diarrhea, here's why

2024-08-10 19:01:00, Blog CNA

Experts: Olympic marathon swimmers likely to have diarrhea, here's why

Illustrative photo

Whether you're watching from afar, cheering, competing in the Olympics, every event is exciting from start to finish, but not as exciting as waiting to see what disease you might get from participating.

In fact, experts have warned that any athlete who competes in the murky waters of Paris' Seine River runs the risk of contracting diarrhea afterward.

"I would never have chosen the Seine," Davey Jones, professor of environmental science and public health at Bangor University, told BBC Science Focus.

"I know it's iconic, but it also goes through an extremely urbanized area which is always a recipe for disaster when it comes to potential exposure to chemicals or biological pathogens."

So how bad can it be?

According to Jones, we're unlikely to see any illnesses anytime soon after the open water marathons on Thursday and Friday. "The danger will come the next day when they have diarrhea," he says. "They'll probably recover fairly quickly within a week or two."

Some athletes have also expressed concern after Tuesday's training session in the Seine was called over concerns about levels of faecal matter in the water. The session had been canceled five times before due to river pollution.

"I think if someone says they're not worried at all, they're probably lying," Austrian swimmer Felix Auböck told The Associated Press. "I'm worried. I just hope and trust the organization in the sense that they let us in when it's safe enough to do so. But, of course, you're worried because nobody wants to get sick."

A viral threat

According to Jones, part of the problem is that we're not testing for the right things when deciding whether water is safe to swim in. Organizers have repeatedly canceled training sessions and even postponed events due to unsafe levels of E.coli bacteria being present in tests.

While E.coli is certainly a risk, Jones says, “Evidence suggests that many of us get sick in water from viruses, and viruses behave very differently from E.coli. So if you just measure E.coli, it doesn't give any information about the risk of viruses."

In fact, Jones' research team has observed ear infections as a classic post-swimming illness, as well as norovirus (vomiting).

"These things are in the population all the time. "Whenever there is a sewage spill, for example, in the Seine, the norovirus is released into the water," he added. "Theoretically you only need to ingest 1-10 viral particles to get sick. And when we're sick, every time we go to the bathroom, we release trillions of these viral particles."

These evils spread through water directly from sewage into our homes. While this waste is usually treated before being released into rivers like the Seine, the treatment may not completely eliminate the risk of disease. Even in the best UK treatment works, 0.1 per cent of sewage still escapes. "And 0.1 percent is a lot," says Jones.

In addition, these sewers are designed to overflow after heavy rain as rainwater fills their capacity. Effluent, known as 'stormwater', is a mixture of rainwater and raw sewage, and flows straight into the river.

Heavy rain, of course, delayed the first Olympic outdoor swimming event of the year. Although the Seine is a massive river, the dilution must be great to eliminate the risk from these pathogens. Athletes' body suits protect them to some extent, but they can't keep their heads above water all the time or stop their mouths from opening.

According to Prof David Werner, an environmental systems modeling expert at Newcastle University, it would be a very difficult job to properly clean the Seine: “Clean rivers require large mitigation measures. In a city like Paris with a high population and predominantly urban land use, the challenge to achieve washing water quality in an urban river will be great.”

Additionally, Werner's research has shown that drainage systems for roofs and streets also release enough pathogens into the water to make washing water unsafe.

So would these experts swim in Siena?

"Intuitively I wouldn't swim in the river that flows through Paris after heavy rain," says Werner.

But given that the Seine has been selected and the open water events are ongoing, Jones sees it as an opportunity for this “big scientific study to see how many people get sick.

"I wish them luck."

About the experts

Prof Davey Jones holds a Professorship in environmental science and public health at Bangor University. He has advised the UK and Welsh Government on their policies on COVID-19, public health, agriculture, waste and climate change, including being part of SAGE's sub-committee on COVID-19 and the environment. His research has been published in the Journal of Ecology, Journal of Virological Methods and Nature.

David Werner is a professor of environmental systems modeling at the University of Newcastle. His research has been published in the journals Water Science & Technology, Science of the Total Environment and Environmental Pollution./ Adapted from CNA