The Evolving Epidemiology of Methicillin-Resistant Staphylococcus aureus at a University Hospital

Abstract

Objective: To describe the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at a university hospital during a 14-month period. Design: Prospective laboratory-based surveillance for MRSA with descriptive epidemiology based on medical chart review and characterization of strains by DNA typing, using pulsed-field gel electrophoresis (PFGE). Setting: An 850-bed tertiary care university hospital. Patients: Patients with clinical isolates of MRSA. Main Outcome Measure: Determination whether MRSA isolates were community- or hospital-related. Results: Among 87 patients with MRSA, 36 (41%) had community-acquired infections. Community acquisition was associated with recent hospitalization, previous antibiotic therapy, nursing home residence, and intravenous drug use. Greater than 3 months had elapsed from the time of discharge for 13 (62%) of the 21 patients with community-acquired isolates hospitalized within the last year. Eight patients (22%) with community-acquired MRSA had no discernible risk factors. PFGE allowed differentiation of 35 distinct whole-cell DNA patterns; heterogeneity was seen among both nosocomial and community-acquired isolates, with few instances of cross-transmission. Conclusions: Our data suggest an increase in community acquisition of MRSA. PFGE demonstrated heterogeneity of MRSA isolates from both the community and the hospital setting.