Pollution of coastal waters by sources including sewage and farm run-off may be the cause, experts suggest

People who swim in the sea are at significantly higher risk of stomach bugs, ear problems and other illnesses than those who stick to the sand, research suggests.



The team behind the findings suggest the increased chances of becoming unwell may be down to pollution of coastal waters by sources such as farm run-off and sewage.



“I think there is a perception in high income countries like the UK that the risk of experiencing illness following bathing in the sea is negligible, but what we found is that there is a significant increase in the chances of getting sick,” said Dr Anne Leonard, co-author of the research from the University of Exeter Medical School.



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Writing in the International Journal of Epidemiology, Leonard and colleagues describe how they scrutinised data from 19 studies focusing on waters of countries including the US, UK, Spain and Norway.



While the team were not able to estimate the exact chance of falling sick, analysis of data from six studies revealed that sea bathers had 86% greater odds of having any illness than those who did not spend time in the sea. Furthermore, analysis of data from six studies revealed that bathers had more than twice the odds of experiencing at least one symptom of an ear ailment.

A large number of the studies found that bathers had a greater risk of at least one symptom of gastrointestinal illness, with data pooled from 12 studies showing bathers had 44% higher odds of diarrhoea than those who didn’t go into the sea, and six studies taken together suggesting that bathers had a 27% higher chance of stomach ache.



The team also found that one study showed a greater chance of bathers having urinary tract infections caused by antibiotic resistant bacteria, including E. coli.



While the studies covered a number of different countries, there appeared to be little difference in increased risks based on location.



However the authors caution that there were limitations, including that many of the studies relied on self-report, varied in sample size and that people who chose not to go into the sea might have different health status to those who liked to go for a splash. What’s more, many of the studies were based on observation, meaning that it is not clear whether bathing itself is behind the increased risk of the various illnesses.



Leonard said the study did not mean that people should stop spending time in the sea. “I think it is important that people know what the risks are so that they can make an informed decision whether or not they want to go bathing, but also what they can do to minimise their risks,” she said.

“We think that the microorganisms responsible for some of these infections, like bacteria and viruses, enter beach water through sewage from people’s homes and also animal sewage,” she added, noting that both are more likely to wash into the sea when it rains, and that swimmers should avoid going into the sea after rainfall.

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Dr Francis Hassard, a microbiologist at Cranfield University who was not involved in the study, welcomed the findings, noting that it could help people to realise the risks of infection and choose whether, or where, to bathe.

“Substantial efforts have been made to help clean up our beaches in recent years, however the results from this study lead to the question: is it enough?” he said.

Kate Rew, director of the Outdoor Swimming Society, said that bathers can take precautions to reduce the chances of becoming ill, including washing hands before eating after a swim, swimming on Blue Flag beaches, and keeping an eye on water quality via the Environment Agency website.

But, she stressed, sea swimmers should not hang up their goggles just yet, noting benefits that include increased fitness, better circulation and improved mood. “Regular and daily sea bathers are often parts of thriving local communities and get far more from their swims than this reported increased occasional risk of infection – pros of sea bathing include a thriving social group, and all the fun and support that community provides,” she said.