Evaluation of the negative predictive value of methicillin-resistant Staphylococcus aureus nasal swab screening in patients with acute myeloid leukemia

Objective:Methicillin-resistant Staphylococcus aureus (MRSA) nasal swabs are utilized to guide the discontinuation of empiric MRSA therapy. In multiple studies, MRSA nasal swabs have been shown to have a negative predictive value (NPV) of ~99% in non-oncology patients with pneumonia and other infections. We evaluated the performance characteristics of a negative MRSA nasal swab in the acute myeloid leukemia (AML) populaion to determine its NPV.Design:Retrospective chart review.Patients:This study included adult AML patients with a suspected infection and a MRSA nasal swab collected between 2013 and 2018.Methods:MRSA nasal swab and culture-documented infections were identified to determine the sensitivity, specificity, NPV, and positive predictive value of the MRSA nasal swabs.Results:In total, 194 patients were identified, and 484 discrete encounters were analyzed. Overall, 468 (97%) encounters had a negative MRSA nasal swab upon admission with no cultured documented MRSA infection during their hospitalization. However, 3 encounters (0.6%) had a negative MRSA nasal swab with a subsequent cultured documented MRSA infection during their admission. Identified infections were bacteremia (n = 2) and confirmed pneumonia (n = 1). MRSA nasal swab had a sensitivity of 62% (95% CI, 0.24–0.91), specificity of 98% (95% CI, 0.96–0.99), positive predictive value of 38% (95% CI, 0.21–0.6), and NPV of 99% (95% CI, 0.98–1).Conclusions:A negative MRSA nasal swab has a 99% NPV for subsequent MRSA infections in AML patients with no prior history of MRSA colonization or infection. Based on these findings, a negative MRSA nasal swab can help guide de-escalation of empiric MRSA antibiotic therapy.