Circling sharks and empty air tanks may haunt scuba divers' imaginations, but ordinary microbes are a far more probable hazard. A new study takes a stab at quantifying the risks that waterborne bacteria and viruses pose to divers.
While scientists regularly measure bacterial concentrations in waters used by beachgoers, they don't test all the sites visited by divers, surfers, and kayakers. What's more, researchers don't know how much of the water these people swallow, says microbiologist and mathematical modeler Jack Schijven of the National Institute of Public Health and the Environment in Bilthoven, the Netherlands.
To begin measuring the microbial risk to divers, Sehijven and his institute colleague Ana Maria de Roda Husman provided a questionnaire to 233 professional divers and posted a similar survey online for about 26,000 recreational divers in the Netherlands. Thirty-seven pros--who do underwater-construction or search-and-rescue work, for example--and 483 amateurs responded. They supplied data on illnesses they'd had in the past year, how many dives they'd made in various aquatic environments, and what volume of water they'd swallowed on a typical dive.
The researchers focused on skin, ear, eye, respiratory, or gastrointestinal symptoms, which might have been caused by infections acquired during dives. Most respondents said that they'd had at least one such illness. Diarrhea and ear problems topped the list.
"Only 20 percent of the divers stated that they did not have any complaint at all," Schijven says. "We were really astonished."