Background:  Outbreaks of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) among HIV-infected men who have sex with men (MSM) have been increasingly reported. In many HIV clinics, including ours, the majority of skin and soft tissue infections are now caused by community-acquired MRSA. However, the role of S. aureus nasal colonization in the pathogenesis of these infections remains poorly understood. We hypothesized that nasal colonization with community-acquired MRSA would exceed that of methicillin-susceptible S. aureus (MSSA), akin to observations that the incidence of clinical disease from community-acquired MRSA exceeds that of community-acquired MSSA in our population. To test this hypothesis, we performed a pilot survey of S. aureus nasal colonization among HIV-infected MSM.

Methods:  We prospectively surveyed HIV-infected MSM followed in a medical center HIV clinic. After informed consent was obtained, patients were administered a questionnaire on community-acquired MRSA risk factors and a nasal swab for S. aureus was performed.

Results:  Of 158 enrolled subjects, 43 (27%) had nasal colonization with S. aureus. Of these, 36 (84%) were colonized with MSSA and 7 (16%) with MRSA. Among subjects responding to the questionnaire, MRSA colonized subjects were more likely than those not colonized with MRSA to have had a skin infection in the past 6 months (67% [4 of 6] vs 18% [26 of 148], p = 0.03) and to have had close contact in the past 6 months with someone with a skin infection (60% [3 of 5] vs 5% [7 of 140], p < 0.01). Six subjects (4%) had clinical MRSA skin and soft tissue infection in the 6 months prior to the survey. Of these, 1 was colonized with MSSA, 1 with MRSA, and 4 were not colonized with S. aureus. Only 1 patient had an MSSA skin and soft tissue infection in the prior 6 months and he was not nasally colonized with S. aureus at the time of study enrollment.

Conclusions:  Although most skin and soft tissue infections in our clinic population are caused by community-acquired MRSA, the majority of S. aureus nasal colonization is with MSSA. This suggests that either the “attack rate” of nasal community-acquired MRSA is higher than nasal MSSA strains, or that infections are not commonly associated with nasal colonization. These data are consistent with other reports suggesting that skin–skin or skin–fomite contact may be the predominant route for community-acquired MRSA acquisition. These findings may lead to improved strategies for preventing community-acquired MRSA infection and transmission.

Keywords: MRSA; MSM; epidemiology