Evaluation of single vs pooled swab cultures for detecting MRSA colonization

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-mu L sterile saline, and these suspensions were used individually and as pooled samples to inoculate two different chromogenic media [MRSA SMART (bio-Merieux, Marcy-l'Etoile, 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. (C) 2017 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.