Evaluation of the Xpert Methicillin-Resistant Staphylococcus aureus (MRSA) Assay Using the GeneXpert Real-Time PCR Platform for Rapid Detection of MRSA from Screening Specimens

• Published in: Journal of Clinical Microbiology Vol. 46; no. 10; pp. 3285 - 3290
• Main Authors: Rossney, Angela S, Herra, Celine M, Brennan, Gráinne I, Morgan, Pamela M, O'Connell, Brian
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.10.2008; American Society for Microbiology (ASM)
• Subjects: Bacteriological Techniques - methods; Bacteriology; Biological and medical sciences; Carrier State - microbiology; Fundamental and applied biological sciences. Psychology; Humans; Ireland; Mass Screening - methods; Methicillin Resistance; Microbial Sensitivity Tests - methods; Microbiology; Miscellaneous; Nose - microbiology; Pharynx - microbiology; Polymerase Chain Reaction - methods; Predictive Value of Tests; Sensitivity and Specificity; Skin - microbiology; Staphylococcus aureus - drug effects; Staphylococcus aureus - genetics; Ireland; Polymerase chain reaction; Microbiology; Bacteria; Micrococcales; Micrococcaceae; Detection; Real time; Staphylococcus aureus
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.02487-07

The need for rapid methods to accurately detect methicillin-resistant Staphylococcus aureus (MRSA) is widely acknowledged, and a number of molecular assays are commercially available. This study evaluated the Xpert MRSA assay, which is run on the GeneXpert real-time PCR platform (Cepheid) for use in a clinical laboratory. The following parameters were investigated: (i) the limits of detection (LoDs) for four MRSA strains; (ii) the ability to detect isolates of MRSA from a collection representative of MRSA in Ireland since 1974 (n = 114) and the ability to detect control strains with staphylococcal cassette chromosome mec types IVa (IV.1.1.1), IVb (IV.2.1.1), IVc (IV.3.1.1), IVd (IV.4.1.1), V (V.1.1.1), VT, and VI; and (iii) performance in a clinical trial with swabs from nose, throat, and groin/perineum sites from 204 patients, where results were compared with those obtained by direct and enrichment cultures. The average LoD of the four test strains was 610 CFU/ml (equivalent to 58 CFU/swab). All 114 MRSA isolates and 7 control strains tested were detected. Sensitivity, specificity, and positive and negative predictive values for clinical specimens from all sites investigated were 90%, 97%, 86%, and 98%, respectively, but throat specimens yielded poor sensitivity (75%). Sensitivity, specificity, and positive and negative predictive values for nasal specimens were 95%, 98%, 90%, and 99%, respectively. Overall, the assay was rapid and easy to perform, but performance might be enhanced by the inclusion of an equivocal interpretive category based on analysis of all available amplification data.