Natural history of community-acquired methicillin-resistant Staphylococcus aureus colonization and infection in soldiers.
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.
Department of Medicine, Brooke Army Medical Center, Fort Sam Houston, TX 78234-6200, USA. Michael.Ellis2@amedd.army.mil
Michael W
MW
Ellis
Duane R
DR
Hospenthal
David P
DP
Dooley
Paula J
PJ
Gray
Clinton K
CK
Murray
D000038:Abscess / Q000382:microbiology; D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002353:Carrier State; D002481:Cellulitis / Q000382:microbiology; D017714:Community-Acquired Infections / Q000188:drug therapy* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D008889:Military Personnel; D009666:Nose / Q000382:microbiology; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000453:epidemiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity; D037521:Virulence Factors / Q000235:genetics
D000900:Anti-Bacterial Agents; D037521:Virulence Factors