Prevalence of methicillin-resistant Staphylococcus aureus nasal carriage in the community pediatric population

Background.

Reports from various geographic regions indicate that the prevalence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infection is increasing. The primary reservoir is the anterior nares; nasal carriage is a risk factor for infection in a variety of populations. Little is known about MRSA nasal carriage rates among children in Nashville, TN and the associated likelihood of community MRSA transmission.

Methods.

Nasal swabs were collected from 500 children at well-child visits at either a university hospital pediatric clinic or a private pediatric office. Cultures were plated onto selective staphylococcal media, with or without oxacillin. S. aureus isolates were confirmed by coagulase tube testing. Antibiotic susceptibilities were determined for suspected methicillin-resistant S. aureus isolates by standard broth microdilution methods (National Committee for Clinical Laboratory Standards). Pulsed field gel electrophoresis was used to evaluate epidemiologic relatedness. PCR testing was done to assess for the mecA gene. A parent questionnaire was administered regarding MRSA risk factors.

Results.

Four patients had oxacillin-resistant S. aureus isolates (MIC ≥ 4 μg/ml), and two had borderline resistant isolates (MICs = 1 and 2 μg/ml). One of the borderline-resistant isolates and one of the MRSA isolates had pulsed field gel electrophoresis typing results indicating close relatedness. The mecA gene was present in all resistant isolates and one of the borderline-resistant isolates. Only having a household member employed in a hospital was associated with a greater risk of MRSA nasal carriage (odds ratio, 9.6; P = 0.008).

Conclusions.

MRSA nasal colonization is present within Nashville's healthy pediatric population. Children with household contacts employed in a hospital are significantly more likely to be colonized.