Natural history of community-acquired methicillin-resistant Staphylococcus aureus colonization and infection in soldiers

Clin Infect Dis. 2004 Oct 1;39(7):971-9. doi: 10.1086/423965. Epub 2004 Sep 2.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Abscess / microbiology
  • Adolescent
  • Adult
  • Anti-Bacterial Agents / pharmacology
  • Carrier State
  • Cellulitis / microbiology
  • Community-Acquired Infections / drug therapy*
  • Community-Acquired Infections / epidemiology*
  • Female
  • Humans
  • Male
  • Methicillin Resistance*
  • Military Personnel*
  • Nose / microbiology
  • Prospective Studies
  • Risk Factors
  • Staphylococcal Infections / drug therapy*
  • Staphylococcal Infections / epidemiology*
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / pathogenicity
  • Virulence Factors / genetics


  • Anti-Bacterial Agents
  • Virulence Factors