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 1.7 h, compared to 25.7 h 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.