(525) Utility of MRSA Nasal Surveillance Screening in Critically Ill Patients

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) pneumonia is associated with increased hospital mortality, 28-day mortality, and mechanical ventilation days compared to other intensive care unit (ICU) infections. Current evidence evaluating MRSA surveillance screening may not be generalizable to critically ill patients and the sustainability of surveillance screening over time or antibiotic exposure has not been previously explored. This study evaluated the diagnostic performance characteristics (DPC) of MRSA nasal swabs for the prediction of MRSA pneumonia in a critically ill population.

Methods: This single-center, retrospective study included patients admitted to an adult ICU who had a respiratory culture and MRSA nasal swab obtained up to 30 days prior to respiratory culture result. The primary outcome described MRSA nasal swab DPC for MRSA pneumonia. Secondary outcomes included DPC at specific time cohorts from swab to respiratory culture, anti-MRSA antibiotic exposure time cohorts, independent risk factors for discordant swab results, and time to nosocomial MRSA colonization.

Results: A total of 137 patients were included. The primary outcome DPC of MRSA nasal swab: negative predictive value (NPV) 95.8%, positive predictive value (PPV) 35.3%, sensitivity 54.5%, and specificity 91.3%. At < 24 hours from MRSA nasal swab to respiratory culture the NPV was 98.8%, 90.9% by 25-48 hours, and 93.3% by 3-7 days. Patients who received anti-MRSA antibiotics for < 48 hours had a NPV 94.1% compared to NPV 96.7% with no antibiotic exposure. No independent risk factors were identified for discordant swab results. 29 patients had sequential swabs collected during hospital admission, all of which remained negative.

Conclusions: MRSA nasal swab DPC demonstrated a NPV of 95.8% in this ICU population. NPV declined as early as 25-48 hours following MRSA nasal swab but remained >90% up to 7 days post-collection. Receipt of anti-MRSA antibiotics for < 48 hours prior to screening did not have a significant impact on the NPV of MRSA nasal swabs in critically ill patients. ICU patients receiving sequential swabs did not test positive for new MRSA colonization.