Asymptomatic Drug Resistant Staphylococcus Detected

Methicillin-resistant Staphylococcus aureus (MRSA) can be detected in asymptomatic patients in an emergency department (ED) setting.

The prevalence of asymptomatic MRSA colonization in ED patients is poorly described, particularly in the absence of skin and soft tissue infection-related complaints.

A study to assess the prevalence of nasal and extranasal staphylococcal colonization in ED patients was carried out at the Boston University School of Medicine (Boston, MA, USA). The scientists evaluated the risk factors, and characterized the strains by molecular techniques. They actively surveyed 400 patients presenting to the ED. Testing was conducted on anterior nares, oropharynx, palms, groin, perirectal area, wounds, and catheter insertion sites. Swabs taken from the various sites were cultured and any S. aureus, whether sensitive (MSSA) or resistant (MRSA) to methicillin, were characterized by a multiplex polymerase chain reaction assay.

The prevalence of colonization with MSSA was 39%, and prevalence of colonization with MRSA was 5%. Among MRSA-colonized subjects, an extranasal site tested positive in 80% of subjects, and 45% had exclusive extranasal colonization. Human immunodeficiency virus (HIV) infection showed the strongest association with MRSA colonization, with a nearly 14-fold increased risk. Among factors at least tripling the risk was a history of diabetes, presenting from a nursing home, and playing contact sports. However, among those who were colonized, 20% had no risk factors for colonization and 45% were colonized only at sites other than the nose. Of those colonized with MRSA, 55% were infected with the USA300 strain which often carries the Panton-Valentine leukocidin virulence factor and is responsible for invasive skin and soft tissue infections, necrotizing pneumonia, necrotizing fasciitis, and other serious infections in otherwise healthy hosts.

Elissa M. Schechter-Perkins, MD, M.P.H., the lead author of the study, said, "These findings suggest that current programs that screen for MRSA, which typically screen for nasal MRSA colonization among patients perceived to be at high-risk, may actually be missing a large number of patients actually colonized with MRSA. This has implications for spread of MRSA colonization and subsequent infections that nasal screening programs aim to prevent.” The study was published online on January 15, 2011, in Annals of Emergency Medicine.

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Boston University School of Medicine