Rapid molecular testing for Staphylococcus aureus bacteraemia improves clinical management

Introduction. Staphylococcus aureus bacteraemia (SAB) causes significant morbidity and mortality. Standard diagnostic methods require 24-48 h to provide results, during which time management is guideline-based and may be suboptimal. Aim. Evaluate the impact of rapid molecular detection of S. aureus in positive blood culture bottle fluid on patient management. Methodology. Samples were tested prospectively at two clinical centres. Positive blood cultures with Gram-positive cocci in clusters on microscopy were tested with the Xpert MRSA/SA blood culture assay (Cepheid), as well as standard culture-based identification and antimicrobial sensitivity tests. Results were passed to clinical microbiologists in real time and used for patient management. Results. Of 264 blood cultures tested (184 and 80 from each centre), S. aureus was grown from 39 (14.8%) with one identified as methicillin-resistant S. aureus; all Xpert results agreed with culture results. Median turnaround time from culture flagging positive to result reporting for Xpert was 1.7h, compared to 25.7h for species identification by culture. Xpert results allowed early changes to management in 40 (16.8%) patients, with Xpert positive patients starting specific therapy for SAB and Xpert negative patients stopping or avoiding empiric antimicrobials for SAB. Conclusion. Rapid and accurate detection of S. aureus with the Xpert MRSA/SA BC assay in positive blood culture bottles allowed earlier targeted patient management. Negative Xpert results are suggestive of coagulase negative staphylococci, allowing de-escalation of antimicrobial therapy if clinically appropriate.