Evaluation of single vs pooled swab cultures for detecting MRSA colonization

Abstract

Background: The costs and laboratory workload arising from meticillin-resistant Staphylococcus aureus (MRSA) screening could be reduced markedly by processing nose, throat and skin swabs from one person in a single culture broth (specimen pooling). The purpose of this study was to evaluate the sensitivities and times for MRSA detection using a variety of approaches to processing of individual and pooled swabs.

Methods: Four hundred and seventeen swabs from 139 subjects with a history of MRSA colonization (three swabs per subject - nose, throat and skin) were submitted. Swabs were suspended in 200-μL sterile saline, and these suspensions were used individually and as pooled samples to inoculate two different chromogenic media [MRSA SMART (bioMėrieux, Marcy-l'Étoile, Paris, France) and CHROMagar MRSA (CHROMagar, Paris, France)] and Todd-Hewitt Broth; the latter cultures were then subcultured on to the same chromogenic media.

Results: MRSA was detected from at least one specimen in 75 subjects (50.4%). The diagnostic sensitivities of pooled surveillance cultures compared with single cultures were 97% and 93% for direct and enrichment cultures, respectively. Enrichment culture of either individual or pooled samples had no benefit compared with direct culture (P>0.05).

Conclusions: Pooling of MRSA screening swabs for either direct culture on chromogenic agar or enrichment culture is suitable for routine use.

Keywords: Detection of colonization; MRSA; Pooling; Surveillance cultures.