2683. Evaluation of the Negative Predictive Value (NPV) of Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Swab Screening in Acute Myeloid Leukemia Patients

BACKGROUND: Methicillin-Resistant Staphylococcus aureus (MRSA) nasal swabs are utilized to guide discontinuation of empiric MRSA therapy. In multiple studies, MRSA nasal swabs has been shown to have a negative predictive value (NPV) of ~99% in non-oncology patients with pneumonia and other infections. At Yale New Haven Hospital (YNHH), a negative MRSA nasal swab is utilized in acute myeloid leukemia (AML) patients to de-escalate empiric MRSA antibiotic therapy. The primary endpoint was to assess the percentage of patients with a negative MRSA nasal swab who developed a culture documented (CD) MRSA infection during their admission. Secondary endpoints included the number of MRSA nasal swabs that were initially negative but converted to positive, and the types of MRSA infections. METHODS: This was a retrospective chart review of AML patients with a suspected infection and a MRSA nasal swab collected at YNHH between 2013 and 2018. Patients were excluded if < 18 years old, prior confirmed MRSA infection or positive MRSA nasal swab within the past year. RESULTS: 194 patients were identified with 484 discrete encounters analyzed. Hematopoietic stem cell transplantation occurred in 83 (43%) patients. A total of 468 (97%) encounters had a negative MRSA nasal swab upon admission with no CD MRSA infection during their hospitalization. Three encounters (0.6%) had a negative MRSA nasal swab with a subsequent CD MRSA infection during their admission. Identified infections were bacteremia (2) and pneumonia (1). Median duration from the negative MRSA nasal swab to CD infection was 16 days. Thirteen encounters (3%) had a positive MRSA nasal swab, 5 of which had a CD MRSA infection. Infections included bacteremia (3), pneumonia (2), and sputum with negative chest X-ray (1). MRSA nasal swab had a sensitivity of 57% (CI 0.56–0.58), specificity of 98% (CI 0.98–0.98) positive predictive value of 31% (CI 0.3–0.32), and NPV of 99% (CI 0.99–0.99). CONCLUSION: The results of this retrospective study demonstrate that 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 in this immunosuppressed population. DISCLOSURES: All authors: No reported disclosures.