The evolving epidemiology of methicillin-resistant Staphylococcus aureus at a university hospital.

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.