MRSA reported at public beaches in Washington

Samples from five beaches around Puget Sound tested positive for a multidrug resistant form of Staphylococcus aureus. These beaches join a growing list of beaches around the country that have been found to contain this infection, according to a researcher who spoke on the findings yesterday at the American Society for Microbiology's Interscience Conference on Antimicrobial Agents and Chemotherapy in San Francisco.

Marilyn Roberts, PhD, and other microbiologists from the University of Washington in Seattle examined sand and water samples that were collected from 10 Washington beaches between February and September of 2008. They identified Staphylococcus aureus on nine public beaches, and seven of the 13 samples were multidrug resistant, demonstrating resistance to vancomycin as well as other medications.

Roberts said their team expected to find more MRSA that was community-acquired from the samples; however, most of the samples resembled hospital-acquired MRSA. The researchers found three samples 10 miles apart that were almost identical, suggesting that they may have come from the same source.

She noted that the average water temperature in this area is 50º, so most people do not swim there, making the source likely environmental and not human. However, she added, "where all of these organisms are coming from is not clear." She noted that MRSA thrive in salt water environments, and it is not clear how well this bacteria would survive in fresh water.

Last year, Roberts' team reported finding enterococci at several West Coast beaches. And earlier this year, another researcher team reported finding this bacteria in ocean water samples collected in Miami. She noted in the Miami study those who had dug in the sand or had been buried in sand were more likely to be colonized with MRSA. – by Colleen Zacharyczuk

For more information:

Roberts M. #C2-146. Interscience Conference on Antimicrobial Agents and Chemotherapy; San Francisco: Sept. 11-15, 2009.