title: 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.
abstract: 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), V(T), 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.
authors.affiliation: National MRSA Reference Laboratory, St. James's Hospital, James's St., Dublin 8, Ireland. arossney@stjames.ie
authors.forename: Angela S
authors.initials: AS
authors.lastname: Rossney
authors.forename: Celine M
authors.initials: CM
authors.lastname: Herra
authors.forename: Gráinne I
authors.initials: GI
authors.lastname: Brennan
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Morgan
authors.forename: Brian
authors.initials: B
authors.lastname: O'Connell
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D002353:Carrier State / Q000382:microbiology; D006801:Humans; D007494:Ireland; D008403:Mass Screening / Q000379:methods; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods; D009666:Nose / Q000382:microbiology; D010614:Pharynx / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000379:methods*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D012867:Skin / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics