Methicillin-resistant staphylococcus aureus nucleic acid amplification test (MRSA NAAT): Evaluation of predictive performance in skin and soft tissue infections

Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) NAAT polymerase chain reaction (PCR) has been a valuable tool for de-escalating vancomycin, including for management of skin and soft tissue infections (SSTIs). Providers have reported instances where a negative MRSA NAAT has led to narrowing antibiotics, but the wound culture revealed MRSA growth. Previous research shows MRSA NAAT negative predictive value (NPV) for all SSTIs to be between 80% and 98.4%. In this study, we assessed the NPV of MRSA NAAT PCR to determine if it is lower for SSTIs than previously reported. Materials and Methods: Retrospective, single Center study evaluating 162 patients with diagnosis of SSTI between November 2022 and January 2025. Analyzed impact of data using sensitivity, specificity, positive predicative value (PPV), NPV, positive likelihood ratio, and negative likelihood ratio. Results: This population included most purulent infections ( n = 134, 82.7%) and patients with a diagnosis of cellulitis ( n = 65, 40.1%). Of the patients included in this study, 92 (56.8%) had a negative MRSA NAAT PCR with no MRSA growth, 37 (22.8%) had a positive MRSA NAAT PCR with MRSA growth, 15 (9.3%) had a negative MRSA NAAT PCR with MRSA growth, and 18 (11.1%) had a positive MRSA NAAT PCR with no MRSA growth. This data calculated a NPV of 86% (95% confidence interval [CI], 77.6–91.7%) and a PPV of 67.3% (95% CI, 53.2–79%). Conclusion: MRSA NAAT PCR testing is a valuable tool for de-escalation; however, other factors need consideration prior to de-escalation of vancomycin in the setting of SSTIs.