Author(s): Ellis MW, Hospenthal DR, Dooley DP, Gray PJ, Murray CK
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Abstract BACKGROUND: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging pathogen for which the prevalence, risk factors, and natural history are incompletely understood. METHODS: In this prospective observational study, we evaluated 812 US Army soldiers to determine the prevalence of and risk factors for CA-MRSA colonization and the changes in colonization rate over time, as well as to determine the clinical significance of CA-MRSA colonization. Demographic data and swab samples from the nares for S. aureus cultures were obtained from participants at the start of their training and 8-10 weeks later. Over this time period, participants were observed prospectively to monitor for soft-tissue infections. S. aureus isolates were characterized by in vitro examination of antibiotic susceptibilities, mecA confirmation, pulsed-field gel electrophoresis, and Panton-Valentine leukocidin (PVL) gene testing. RESULTS: At the initial sampling, 24 of the participants (3\%) were colonized with CA-MRSA, 9 of whom (38\%) developed soft-tissue infections during the study period. In contrast, 229 participants (28\%) were colonized with methicillin-susceptible S. aureus (MSSA), 8 (3\%) of whom developed clinical infections during the same period (relative risk, 10.7; 95\% confidence interval, 4.6-25.2; P<.001). At follow-up culture, the CA-MRSA colonization rate dropped to 1.6\% without eradication efforts. Previous antibiotic use was a risk factor for CA-MRSA colonization at the initial sampling (P=.03). PVL genes were detected in 66\% of 45 recovered CA-MRSA isolates, including all 9 clinical isolates available for analysis. Of subjects hospitalized, 5 of 6 had PVL-positive CA-MRSA infections. CONCLUSIONS: CA-MRSA colonization with PVL-positive strains was associated with a significant risk of soft-tissue infection, suggesting that CA-MRSA may be more virulent than MSSA. Previous antibiotic use may play a role in CA-MRSA colonization.
This article was published in Clin Infect Dis
and referenced in Journal of Antivirals & Antiretrovirals