(575) Diagnostic Utility of MRSA Nasal Swabs in Lung Abscess and Empyema

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen that colonizes human nares and can be detected with a nasal swab. Empiric antibiotic therapy for MRSA is associated with many adverse drug events and side effects. Previous data have shown high negative predictive value with MRSA swab screening in respiratory infections such as pneumonia. However, similar data for empyema and lung abscesses are lacking.

Methods: This was a retrospective, non-interventional cohort study of adult patients of all acuity levels with ICD-10 codes for empyema and/or lung abscess admitted to SSM hospitals across 4 states (Missouri, Oklahoma, Illinois, and Wisconsin) from January 1, 2017, to December 31, 2021. De-identified medical record data was obtained from the Saint Louis University-SSM Health Care System’s Virtual Data Warehouse. MRSA nasal swab results collected within 7 days of a respiratory culture were analyzed for positive predictive value (PPV), negative predictive value (NPV), specificity, and sensitivity.

Results: This study included 390 patients and 397 total screening tests. Only unique patient encounters were included in the study. Included patients were predominantly male (66.4%) and Caucasian (74.6%), with a mean age of 59 years. The NPVs of MRSA nasal swabs for lung abscesses and empyema were 98%, 95% CI (91-100%) and 97%, 95% CI (95-99%), respectively. Specificity was 97%, 95% CI (89-99%) for lung abscess and 96%, 95% CI (94-98%) for empyema. Sensitivity was 6%, 95% CI (2-15%) for lung abscess and 39%, 95% (CI 18-64%) for empyema.

Conclusions: This study suggests that a negative MRSA nasal swab obtained within 7 days of a pleural fluid culture and/or lung abscess culture may be useful for predicting the absence of MRSA infections in lung abscesses and empyema. These results add to a growing body of literature suggesting diagnostic utility of MRSA swabs for these infections. Thus, MRSA swabs can be useful stewardship tools to quicken antibiotic tailoring and decrease empiric anti-MRSA antibiotic use in lung abscesses and empyema, including in critically ill patients.