Swimming in oceans ups infection risk

Washington DC: Swimming in the ocean alters the skin microbiome and may increase the likelihood of infection, a study has found.

The researchers detected ocean bacteria on all participants after air drying and at six and 24 hours post-swim, but some participants had acquired more ocean bacteria and/or had them persist for longer.

"Our data demonstrate for the first time that ocean water exposure can alter the diversity and composition of the human skin microbiome," said Marisa Chattman Nielsen, a PhD student at the University of California, Irvine in the US.

"While swimming normal resident bacteria were washed off while ocean bacteria were deposited onto the skin," said Nielsen.

The research was motivated by previous studies which have shown associations between ocean swimming and infections, and by the high prevalence of poor water quality at many beaches, due to wastewater and storm water runoff.

Recent research has demonstrated that changes in the microbiome can leave the host susceptible to infection, and influence disease states.

Exposure to these waters can cause gastrointestinal and respiratory illness, ear infections, and skin infections.

The investigators sought nine volunteers at a beach who met criteria of no sunscreen use, infrequent exposure to the ocean, no bathing within the last 12 hours, and no

antibiotics during the previous six months.

The researchers swabbed the participants on the back of the calf before they entered the water, and again after subjects had air dried completely following a ten-minute swim and at six and 24 hours post swim.

Before swimming, all individuals had different communities from one-another, but after swimming, they all had similar communities on their skin, which were completely different from the "before swim" communities. At six hours post swim, the microbiomes had

begun to revert to their pre-swim composition, and at 24 hours, they were far along in that process.