Prevalence and Predictors of Nasal and Extranasal Staphylococcal Colonization in Patients Presenting to the Emergency Department

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common causes of skin and soft tissue infections in patients presenting to the emergency department (ED). The prevalence of asymptomatic MRSA colonization in ED patients is less well described, particularly in the absence of a skin and soft tissue infection-related complaint. The goals of this study are to assess the prevalence of nasal and extranasal staphylococcal colonization in ED patients, evaluate risk factors, and molecularly characterize the strains. We performed active surveillance for methicillin-susceptible S aureus (MSSA) and MRSA colonization in 400 subjects presenting to an urban ED. Risk factor assessment was performed and culture testing was conducted on anterior nares, oropharynx, palms, groin, perirectal area, wounds, and catheter insertion sites. Multiplex polymerase chain reaction was used to identify the USA300/400 clonal types. The prevalence of colonization with MSSA was 39% (95% confidence interval 34.2% to 44.0%), and prevalence of colonization with MRSA was 5% (95% confidence interval 3.1% to 7.6%). Among MRSA-colonized subjects, an extranasal site tested positive in 80% of subjects, and 45% had exclusive extranasal colonization. USA300 was identified in 55% of MRSA-colonized subjects. The main risk factors for MRSA colonization included HIV infection, diabetes, and participation in contact sports. The overall prevalence of MRSA colonization in this ED population was lower than that reported in other high-risk ambulatory care settings. However, extranasal colonization was present in more than half of MRSA-colonized subjects, and USA300 was the predominant clonal type.