MRSA nasal swab PCR to de-escalate antibiotics in the emergency department.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) nasal swab polymerase chain reaction (PCR) assay has a 96.1-99.2% negative predictive value (NPV) in pneumonia and may be used for early de-escalation of MRSA-active antibiotic agents. Xu (2018), File (2010) [1,2]. OBJECTIVE: The objective of our study was to determine if a negative MRSA PCR nasal swab collected in the emergency department (ED) improves early MRSA-active antibiotic de-escalation. METHODS: A single center observational cohort study used ICD-10 codes to identify records for adults admitted to the ED with a hospital discharge diagnosis of pneumonia. The primary outcome was proportion of patients with early de-escalation on an MRSA-active agent (≤ 1 dose). Secondary outcomes included rate of acute kidney injury (AKI), positive MRSA cultures (blood culture, respiratory sputum, tracheal aspirate), hospital length of stay (LOS), in-hospital mortality, and 30-day readmission rates. RESULTS: A total of 341 patients were included in the study. Of the patients with an MRSA PCR swab, 35.2% of patients with a negative swab received >1 dose of MRSA-active agent compared to 52% of patients without an MRSA nasal swab (p < 0.01). There were no significant differences in secondary outcomes except readmission rate of 1.6% of patients that did not have an MRSA swab in the ED vs 6.6% of patients that received an MRSA swab in the ED. CONCLUSION AND RELEVANCE: MRSA PCR nasal swabs in the ED may serve as a useful tool for early MRSA-active antibiotic de-escalation when treating pneumonia.