Performance of Methicillin-Resistant Staphylococcus aureus Polymerase Chain Reaction Nasal Screening for Ruling Out MRSA Pneumonia in Hospitalized, Immunocompromised Patients

Background: Recent literature demonstrates support for using methicillin-resistant Staphylococcus aureus (MRSA) nasal swab polymerase chain reaction (NaPCR) screening as an antimicrobial stewardship tool aiding early de-escalation of anti-MRSA antimicrobials. However, immunocompromised patients have been underrepresented in previous studies despite increased risk of morbidity and mortality from multidrug-resistant organisms (MDRO). Objective: The purpose of this study was to determine the negative predictive value (NPV) of the MRSA NaPCR in hospitalized, immunocompromised adult patients with suspected pneumonia. Methods: A single-center, retrospective, observational review was conducted of hospitalized, immunocompromised adult patients that had an MRSA NaPCR obtained between March 1, 2020 and January 10, 2021. For inclusion, bacterial cultures must have been collected within 2 weeks after MRSA NaPCR. The primary outcome was the NPV of MRSA NaPCR in hospitalized, immunocompromised patients with suspected pneumonia. Secondary outcomes include NPV in other infections. Results: Between March 1, 2020 and January 10, 2021, 59 patients with 78 unique cultures, including 28 respiratory cultures, were included in the study. The NPV of the MRSA NaPCR for pneumonia was 91.7%. The NPV for bloodstream infections was 100% and for urinary tract infections was 100%, but interpretation of these results should be cautioned due to the small sample sizes. Conclusion: The NPV of MRSA NaPCR in pneumonia remains high in this study. The MRSA NaPCR has utility as a de-escalation tool in hospitalized, immunocompromised adult patients, but larger studies are warranted to evaluate all immunocompromised patient populations.