CARRIAGE OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS AT HOSPITAL ADMISSION

OBJECTIVES: To measure the prevalence of, and to establish predictors for, the nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission. To evaluate mannitol-salt agar with oxa cillin for the simultaneous detection and identification of MRSA from nasal swabs. DESIGN: Three-month prospective case-control survey, with data collected from interviews and computerized databases. The criter ion standard for MRSA detection was culture on Mueller-Hinton agar wit h oxacillin 6 mu g/mL (National Committee for Clinical Laboratory Stan dards method). SETTING: 320-bed tertiary-care hospital. PATIENTS: 387 patients screened within 24 hours after admission, including 10 MRSA c arriers (cases), 291 patients with no S aureus, and 86 patients with m ethicillin-susceptible S aureus. RESULTS: The prevalence of MRSA nasal carriage was 2.6%, whereas the prevalence of carriage was 3.1% when b oth nasal and wound cultures were performed. The significant predictor s of carriage were a prior detection of MRSA, open wounds, diabetes me llitus, treatments by injection, prior nursing home stays, visits at h ome by a nurse, and prior antibiotic treatments. Cases had stayed for longer periods in hospitals and had received longer antibiotic treatme nts within a year. Eighty patients (including the 10 cases) had diabet es, had been exposed to healthcare facilities within a year, and had a ntibiotics within 6 months. The sensitivity and negative predictive va lue of nasal swabs on mannitol-salt agar with oxacillin were 60% and 7 1%, respectively. CONCLUSION: MRSA carriage on admission to the hospit al may be an increasing and underestimated problem. Further studies ar e needed to develop and validate a sensitive and specific prediction r ule (Infect Control Hosp Epidemiol 1998;19:181-185).