Risk Factors Associated with Methicillin Resistance amongStaphylococcus aureusInfections in Veterans

Abstract

Background.Methicillin-resistantStaphylococcus aureus(MRSA) is an emerging concern in infectious disease practice. Although MRSA infections occur in a wide variety of anatomic sites, the majority of studies considering the risk factors for methicillin resistance amongS. aureusinfections have focused on MRSA bacteremia.Objective.To describe risk factors associated with methicillin resistance amongS. aureusinfections at different anatomic sites.Methods.We collected information on the demographic and clinical characteristics of patients examined at the Atlanta Veterans Affairs Medical Center withS. aureusinfections during the period from June 2007 through May 2008. We used multivariate logistic regression to describe factors significantly associated with methicillin resistance.Results.There were 568 cases ofS. aureusinfection among 528 patients. We identified 352 cases (62%) of MRSA infection and 216 cases (38%) of methicillin-sensitiveS. aureusinfection. The adjusted odds of methicillin resistance were higher among infections that occurred among patients who had a prior history of MRSA infection (odds ratio [OR], 3.9 [95% confidence interval {CI}, 2.3–6.4]) or resided in a long-term care facility during the past 12 months (OR, 2.0 [95% CI, 1.0-4.0]) but were lower for infections that occurred among patients who had undergone a biopsy procedure during the past 12 months (OR, 0.7 [95% CI, 0.6-0.9]). Most cases of infection were community-onset infections (523 [92%] of 568 cases), and about one-half (278 [49%]) were not healthcare associated.Conclusions.Compared with previous studies of methicillin resistance among patients withS. aureusbacteremia, we found similar factors to be associated with methicillin resistance amongS. aureusisolates recovered from more diverse anatomic sites of infection. Of note, nearly one-half of our cases of MRSA infection were not healthcare associated.