Prevalence of nasal colonization and strain concordance in patients with community-associated Staphylococcus aureus skin and soft-tissue infections.

OBJECTIVE

Determine the prevalence and relatedness of Staphylococcus aureus anterior nares colonization in individuals with community-associated staphylococcal skin and soft-tissue infection (SSTI).

DESIGN

Observational cohort.

SETTING

US Army soldiers undergoing infantry training.

PARTICIPANTS

Trainees who developed SSTI from May 2010 to January 2012.

METHODS

Participants underwent anterior nares culture at the time of presentation for purulent SSTI. We determined the prevalence of S. aureus nasal colonization and strain relatedness between colonizing and clinical isolates with pulsed-field gel electrophoresis (PFGE).

RESULTS

We enrolled 1,203 SSTI participants, of whom 508 had culture-confirmed S. aureus SSTI. Overall, 70% (357/508) were colonized with S. aureus. Phenotypically, concordant colonization was more common with methicillin-susceptible S. aureus (MSSA; 56%; 122/218) than methicillin-resistant S. aureus (MRSA) SSTI (41%; 118/290; P < .01). With PFGE, 48% (121 of 254) of clinical-colonizing pairs were indistinguishable, and concordant colonization was more common with MRSA (53%; 92/173) than MSSA SSTI (36%; 29/81; P < .01). Restricting analysis to concomitant MRSA-MRSA or MSSA-MSSA pairs, 92% (92/100) of MRSA SSTI were indistinguishable, and 40% (29/72) MSSA SSTI were indistinguishable (P < .01). All 92 MRSA pairs were USA300.

CONCLUSIONS

On the phenotypic level, concordant anterior nares colonization with incident staphylococcal SSTI is more common in MSSA than MRSA; however, the opposite is observed when accounting for molecular typing, and MRSA SSTI displays greater concordance. USA300 was responsible for strain concordance with MRSA SSTI. Studies are needed to examine the roles of nasal and extra-nasal carriage, colonization preceding infection, and increased virulence in the pathogenesis of MRSA SSTI.

TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01105767.