Hot summers and crowded beaches: Public health risks to bathers

Staphylococcus aureus are commensal colonizing bacteria in up to 40% of people. These organisms are usually associated with skin infections but are capable of causing serious systemic infections. Recent studies have confirmed that viable S. aureus are shed by people into marine waters, and crowded beaches may pose a risk due to exposure to such bacteria. The aim of these studies were to isolate and characterize S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) from marine waters and sand, with and without bathers present, at a non-point source recreational beach in south Florida, and to identify characteristics that contribute to elevated bacterial levels. MSSA and MRSA were collected from multiple samples of water and sand, with and without the presence of bathers, at a recreation beach in S. Florida. Bacteria were isolated, identified and characterized using a combination of selective growth, biochemical tests, PCR-based identification of S. aureus-specific genes including virulence factors and antimicrobial susceptibility testing. Over 1500 MSSA and 19 MRSA were isolated from sand and water. The majority of MRSA carried genes for virulence factors associated with infection. There was a direct correlation (r=0.44, p=0.057) between the daily average number of bathers and S. aureus in the water. Potentially infectious MRSA are in the marine environment. Correlations between bathers and S. aureus in marine waters suggest that humans are a significant source for possible transmission of these bacteria within recreational beaches and marine waters. As beaches become overcrowded in “hot summers” the risks of transmission and exposure to these potential pathogenic bacteria are likely to increase.