Epidemiological study of Staphylococcus aureus nasal carriage in senior centers

The observation of an increasing number of methicillin-resistant Staphylococcus aureus (MRSA) isolates in some population groups prompted us to study the risk factors and the epidemiological profile of S. aureus nasal carriage in healthy adults 65 years of age and older residing in the province of Segovia. Attention was particularly focused on the possibility that some of the infections were community-acquired. We conducted a prospective and observational study of people who usually visited senior citizen centers in the province of Segovia (Carbonero, Cuéllar, Cantalejo) and its capital. The analysis period took place between January and May 2003. Infections were classified as community-acquired, hospital-acquired or health-care associated. Isolates of methicillin-resistant (MRSA) and methicillin-susceptible S. aureus (MSSA) were studied by pulsed-field gel electrophoresis (PFGE). There were 34 (19.5%) The prevalence of nasal carriage of S. aureus was 19.5% and that for MRSA was 1.1%. Female sex was significantly associated with the carriage state. All S. aureus isolates were mupirocin-susceptible. 100% susceptibility and specificity was obtained through latex agglutination testing. The molecular study showed that the transmission for MRSA was monoclonal and that for MSSA was more policlonal. The results presented here form the basis for similar studies in other Spanish senior citizen centers and provide evidence that MRSA strains are beginning to circulate and are becoming significantly established within the community, thus highlighting the need for implementing control strategies to prevent dissemination.