Evaluation of Xpert MRSA gen 3 and BD MAX MRSA XT for meticillin-resistant staphylococcus aureus screening in a routine diagnostic setting in a low-prevalence area

Screening and pre-emptive isolation of at-risk patients are important aspects of the Danish approach to the prevention of meticillin-resistant Staphylococcus aureus (MRSA) infection, but screening with conventional culture can take up to 3 days for results to become available with attendant costs and disadvantages of prolonged isolation. We sought to evaluate the accuracy, time to availability of results and potential economic benefits of two next-generation MRSA screening assays, Xpert MRSA Gen 3 (GX MRSA) and BD MAX MRSA XT, in a setting of a consolidated laboratory serving a number of hospitals with a low prevalence of MRSA and using enrichment culture as a reference method. Four hundred and forty-seven screening samples together with 49 previously positive MRSA samples were evaluated. Xpert MRSA Gen 3 demonstrated sensitivity, specificity, positive predictive value and negative predictive value of 88.2, 97.9, 62.5 and 99.5%, respectively, and for BD MAX MRSA XT, they were 88.2, 97.4, 57.7 and 99.5%, respectively. Hands-on time was 8.8 and 21.6 min, respectively, for the Xpert MRSA Gen 3 and BD MAX MRSA XT PCR assays when five samples were handled simultaneously. The mean laboratory turnaround time was 2.9 (1-6) hours for the Xpert MRSA Gen 3 assay, 6.5 (2-46) hours for BD MAX MRSA XT and 49.6 (42-122) hours for enriched culture. Despite laboratory costs being higher for the rapid PCR assays, when the costs of isolation are taken into account, the assays offer the potential for significant cost savings.