• Sarah K Perreault, Bailee Binks, Dayna S McManus, and Jeffrey E Topal.
• Department of Pharmacy Services, Yale New Haven Hospital, New Haven, Connecticut.
• Infect Control Hosp Epidemiol. 2021 Jul 1; 42 (7): 853-856.

ObjectiveMethicillin-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.DesignRetrospective chart review.PatientsThis study included adult AML patients with a suspected infection and a MRSA nasal swab collected between 2013 and 2018.MethodsMRSA nasal swab and culture-documented infections were identified to determine the sensitivity, specificity, NPV, and positive predictive value of the MRSA nasal swabs.ResultsIn 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).ConclusionsA 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.

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