Sea swimmers no more at risk of superbugs than non-swimmers, research suggests

Preliminary data contradicts warnings of infections, NUIG academics say

Sea swimmers in Ireland are no more at risk of picking up deadly superbugs than those who do not take a regular dip, preliminary results from a scientific study suggest.

Academics at NUI Galway said they have been "surprised" at the findings, which apparently contradict warnings about the threat of possibly life-threatening infections, after testing hundreds of people from almost every county in the country.

Dr Liam Burke, a microbiologist working on the ongoing study, said it was "great" news for those taking to lakes, rivers and seas, amid concerns about links between antibiotic-resistant superbugs and pollution from sewage, manure and effluent.

“Our preliminary data so far suggests swimmers are not any more likely to pick up these bugs than anyone who doesn’t swim,” he said.

“But it is early days yet. We are hoping to find out if there any significant exposure differences in the groups tested to explain the differences.”

After appealing for swimmers and non-swimmers to take part in the study, more than 1,000 people got in contact. Researchers whittled the number down to 428 – almost half who take a regular dip in open waterways, and slightly more than half who do not. Participants mainly drawn from large coastal populations in Dublin, Galway, Cork and Waterford, provided faecal samples between September 2020 and October 2021.

The team then tested the samples for carbapenemase producing enterobacteriaceae (CPE) and extended spectrum beta-lactamases (ESBLs) – both categorised by the World Health Organisation as "priority one" superbugs.

The bugs can live harmlessly in the guts of healthy people, but can easily spread to more vulnerable people, including those with weaker immune systems, the sick, the very old and the very young.

Outbreaks – mainly in hospital wards – have been increasing in Ireland and worldwide in recent years.

The bugs are resistant to “last resort” antibiotics and are “potentially lethal” if they infect the likes of the blood stream, bladder, lungs or kidneys, says Dr Burke.

Bacteria

While research shows antibiotic-resistant bacteria is present in Irish coastal waters, lakes and rivers, mainly from sewage, waste water and manure running off from farms during heavy rainfall, the extent of the problem is not fully known.

However, the fresh study shows 6 per cent of regular swimmers were found to have been carrying ESBLs compared with 11 per cent – almost double – of those who do not get into the water frequently.

In both groups, 3 per cent of participants were found to be carrying CPE – the same proportion.

“It did surprise us,” says Dr Burke. “If there was going to be any difference in the two groups [water users and non-water users] we thought there could be a small difference the other way around.

“I think it is great for anybody who is swimming regularly. Obviously more work needs to be done – it is only a survey of a relatively small number of people, compared to the overall number of people who swim regularly.

“But it bodes well for those people who are using the sea, that they aren’t at any more risk, it seems, from picking up superbugs than those who don’t.”

Dr Burke stressed the findings are preliminary, and more work is to be done on the genetic sequence of the data, as well as on other exposure risks of participants, such as workplaces and diet.

“I think it would probably be going too far to say swimmers are less likely to pick up these superbugs... but all the evidence we have so far suggests there isn’t any major increased risk for those who swim, against those who don’t swim,” says Dr Burke.

The preliminary findings from the research, funded by the Environmental Protection Agency, are to be presented at the 32nd European Congress of Clinical Microbiology and Infectious Diseases, starting in Lisbon, Portugal, on Saturday.