Point-Counterpoint: Should MRSA nares testing be used as a tool for vancomycin de-escalation outside of pneumonia?

Vancomycin is broadly used to treat gram-positive infections in both inpatient and outpatient settings. Its use is primarily for the treatment of methicillin-resistant Staphylococcus aureus (MRSA), which is a common cause of pneumonia, skin and soft tissue infections, and bloodstream infections. Vancomycin therapy requires close clinical monitoring to maintain therapeutic efficacy and, importantly, patient safety. Vancomycin use is associated with acute kidney injury in up to 20% of cases, a number that can be driven down by pharmacokinetic dosing protocols. However, the best mitigation against adverse outcomes associated with vancomycin is to ensure it is only used when needed and rapidly de-escalated when not. As such, many stewardship programs, who are tasked with the safe and effective use of antimicrobial agents, have focused on optimizing vancomycin use. There is a strong correlation with MRSA colonization and infection, and a negative MRSA nares screen has a good negative predictive value for MRSA pneumonia (although this association is less well documented for other infections). As such, detection of MRSA in nares swabs, by nucleic acid amplification tests (NAATs) or culture, is a logical tool for stewarding vancomycin. However, the application of MRSA screening tests as MRSA diagnostics is complex, as these tests are cleared by the U.S. Food and Drug Administration for the detection of MRSA colonization, and not for therapeutic decision making. In this issue of the Journal of Clinical Microbiology, the issue of MRSA nares tests is debated by a clinical pharmacy team and the laboratory. The authors review the clinical evidence and regulatory background in which an MRSA nares NAAT may be used to inform treatment decisions.