Evaluation of the Xpert MRSA assay for rapid detection of methicillin-resistant from nares swabs of geriatric hospitalized patients and failure to detect a specific SCC type IV variant

C. Laurent (1) , P. Bogaerts (1) , D. Schoevaerdts (2) , O. Denis (3) , A. Deplano (3) , C. Swine (2) , M. J. Struelens (3) , Y. Glupczynski (1)

1 Department of Clinical Microbiology, Laboratoire de Microbiologie
2 Geriatric Unit, Department of Internal Medicine
3 Department of Clinical Microbiology and National MRSA Reference Laboratory

Rapid and reliable detection of methicillin-resistant (MRSA) carriers is crucial for control of MRSA nosocomial transmission. We aimed to evaluate the performance of the GeneXpert real-time PCR system using the Xpert MRSA assay on a collection of 40 representative Belgian MRSA strains and for MRSA screening of geriatric inpatients. Double nasal swabs were used: the first swab for the Xpert MRSA assay and the second for culture onto chromogenic selective medium and enrichment broth. All but 1 of the 40 collection strains were recognized as MRSA by the Xpert MRSA assay. Nares swabs were prospectively collected from 246 inpatients including 25 nasal MRSA carriers. Compared with enriched cultures, the sensitivity, the specificity, and the positive and negative predictive values of the Xpert MRSA assay were 69.2%, 97.7%, 78.3%, and 96.3% respectively. The 7 evaluable false-negative results according to the assay were due to its possible lack of sensitivity (= 3) and to the occurrence of a Belgian MRSA clone carrying a particular staphylococcal chromosomal cassette (SCC) type IV variant ( = 4) not targeted by the current Xpert MRSA assay. Because of the evolution of SCC in MRSA, new primers should be designed and further studies are warranted to ensure continuous monitoring of this assay.

Mots clés: Life Sciences

C. Laurent, P. Bogaerts, D. Schoevaerdts, O. Denis, A. Deplano, et al.. Evaluation of the Xpert MRSA assay for rapid detection of methicillin-resistant from nares swabs of geriatric hospitalized patients and failure to detect a specific SCC type IV variant. European Journal of Clinical Microbiology and Infectious Diseases, 2010, 29 (8), pp.995-1002. ⟨10.1007/s10096-010-0958-3⟩. ⟨hal-00596688⟩