Prevalence of and risk factors for colonization with methicillin-resistant Staphylococcus aureus at the time of hospital admission

OBJECTIVES: To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization among patients presenting for hospital admission and to identify risk factors for MRSA colonization. DESIGN: Surveillance cultures were performed at the time of hospital admission to identify patients colonized with S. aureus. A case-control study was performed to identify risk factors for MRSA colonization. SETTING: A tertiary-care academic medical center. PATIENTS: Adults presenting for hospital admission (N = 974). RESULTS: S. aureus was isolated from 205 (21%) of the patients for whom cultures were performed. Methicillin-sensitive S. aureus was isolated from 179 (18.4%) of the patients, and MRSA was isolated from 26 (2.7%) of the patients. All 26 MRSA-colonized patients had been admitted to a healthcare facility in the preceding year, had at least one chronic illness, or both. In multivariate analyses comparing MRSA-colonized patients with control-patients, admission to a nursing home (odds ratio [OR], 16.5; 95% confidence interval [CI95] 1.4 to 192.1; P =.025) or a hospitalization of 5 days or longer luring the preceding year (OR, 3.91; CI95, 1.1 to 13.9; P =.035) were independent predictors of MRSA colonization. CONCLUSIONS: Patients colonized with MRSA admitted to this hospital likely acquired the organism during previous encounters with healthcare facilities. There was no evidence that MRSA colonization occurs commonly among low-risk individuals in this community. These data suggest that evaluation of recent healthcare exposures is essential if true community acquisition of MRSA is to be confirmed.