Fancy heading down to the beach to swim among a host of pathogens that have come from human feces? If not, then steer clear of public beaches in the US, because no one knows for sure what levels of pathogens exist in the nation's bathing waters. "Current testing practices are seriously flawed," warns public health expert Thaddeus Graczyk at Johns Hopkins University in Baltimore, Maryland.
Graczyk and colleagues sampled water from Maryland's beaches on Wednesdays and Sundays for 11 consecutive weeks during the summer of 2006. They tested for Cryptosporidium parvum and Giardia lamblia, protozoans in human feces that can cause severe, and sometimes fatal, gastrointestinal problems. The pathogens lurked in 30 per cent of samples midweek, but in almost 60 per cent at weekends - levels strongly linked to the number of bathers in the water (Applied and Environmental Microbiology, DOI: 10.1128/AEM.00365-07).
Health inspectors usually test beach waters during the week. "The water should be tested when the numbers of people are higher," says Graczyk. "A lot of beaches would be closed if they tested on weekends." Gracyzk suspects bathers stir up sediment that already contains the microbes, which enter recreational waters primarily through human feces, either directly, through sewage or from surface run-off after heavy rains. He will present his findings next month in Philadelphia at the American Society of Tropical Medicine and Hygiene meeting.