Contribution of two molecular assays as compared to selective culture for MRSA screening in a low MRSA prevalence population

Abstract

Background: As the prompt detection of methicillin-resistant Staphylococcus aureus (MRSA) carriers upon admission is fundamental in the MRSA prevention strategy of our hospital, the infection control team is eagerly seeking the most sensitive and rapid screening method. The aim of this study was to compare the performance of two molecular techniques with a conventional MRSA-selective culture test (Bio-Rad chromogenic MRSASelect) in order to elucidate the suitability of the assays specifically in an expected low MRSA prevalence population.

Patients and methods: The anterior nares and throat of 500 patients and visitors attending the emergency department of Sint-Jan General Hospital between May and June 2007 were sampled, and MRSA carriage was determined by selective culture after enrichment and the BD GeneOhm StaphSR and the Cepheid Xpert MRSA assays.

Results: Eight MRSA carriers were detected by selective culture (1.6% prevalence). The sensitivity, specificity, positive [corrected] predictive value, and negative [corrected] predictive value were 62.5, 99.0, 50.0, and 99.4% for BD GeneOhm StaphSR and 62.5, 97.7, 31.3, and 99.4% for Cepheid Xpert MRSA, respectively.

Conclusions: We conclude that MRSA rapid screening techniques must be interpreted cautiously in a low-prevalence population, as the sensitivity is lower than in selected high-risk populations. MRSA carriers detected with molecular techniques must be confirmed by conventional culture methods for follow-up. The specificity and negative predictive value indicate that molecular rapid methods are worthwhile to be considered in MRSA-preventive strategies.