a1 Departments of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA
a2 Department of Pathology, University of Maryland School of Medicine, Baltimore, MD, USA
a3 VA Maryland Health Care System, Baltimore, MD, USA
To examine the pathogenesis of USA300 MRSA infection in long-term care residents, we performed a retrospective cohort study of 1691 adult residents of two extended-care facilities from 2003 to 2007 to assess whether the risk of subsequent MRSA infection is higher in USA300 MRSA-colonized residents compared to non-colonized residents or non-USA300 MRSA colonized residents. Six per cent of residents were colonized with USA300 MRSA; 12% of residents were colonized with non-USA300 MRSA; and 101 residents developed MRSA infection. The risk of infection was twofold higher in residents colonized with USA300 MRSA compared to residents not colonized with MRSA [adjusted hazard ratio 2·3, 95% confidence interval (CI) 1·1–4·5]. The risk of infection in USA300 MRSA-colonized residents was similar to USA300 MRSA non-colonized residents (relative risk 1·1, 95% CI 0·5–2·3). Our findings show that colonization with USA300 MRSA increases the risk of MRSA infection suggesting a similar pathogenesis.
(Accepted June 15 2011)
(Online publication July 18 2011)