Widespread emergence of methicillin resistance in community-acquired Staphylococcus aureus infections in Denver.

Background: Increasing rates of methicillin resistance among out-patient Staphylococcus aureus infections led us to assess the epidemiology and outcome of a local outbreak.

Methods: A retrospective cohort study of outpatient skin and soft tissue infections due to S aureus in 2003.

Results: From 2002 to mid-2004, the percentage of outpatient S aureus isolates resistant to methicillin increased from 6 to 45%. In multivariate analysis, only male sex and age greater than 18 years were associated with methicillin resistance. Methicillin resistance was common (>15%) among isolates from patients in nearly all subgroups evaluated. Pulsed field gel electrophoresis showed isolates related to USA 300, but methicillin-resistant strains had unusually high rates of quinolone resistance.

Conclusions: A single strain of methicillin-resistant S aureus is responsible for the increase in skin infections in outpatients without traditional risk factors for infection with an antibiotic-resistant strain. In areas with high rates of methicillin-resistant S aureus outpatient infections, we recommend non-beta-lactam antibiotics for initial treatment of skin and soft tissue infections.