Clinical Utility of Methicillin-Resistant Staphylococcus aureus Nare Swabs in a Burn ICU

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen in burn ICUs. Many studies have evaluated the overall utility of MRSA nares swabs for antimicrobial stewardship; however, there is a paucity of data in critically ill burn patients. The purpose of this project was to evaluate the diagnostic performance characteristics of MRSA nares in a burn ICU at an academic medical center.


Methods: This retrospective, single-center chart review included adult burn patients admitted to the Surgical Trauma Burn ICU from July 2020 to September 2024. It excluded patients without a MRSA nares swab and a bacterial culture in the same admission, only a urine culture, or a length of stay less than 48 hours. The primary objective was to determine the overall negative predictive value (NPV) of MRSA nares swabs for MRSA infection in the burn ICU population. Secondary objectives included determining the sensitivity, specificity, positive predictive value (PPV), and the diagnostic accuracy MRSA nares for each specific culture type.


Results: There were 1,105 patients screened and 81 included. Median (IQR) age was 57 (35, 67) years and most were Caucasian (54.3%) and male (80.2%). The most common burn mechanism was flame (48.1%). Median (IQR) total body surface area burn was 21% (7,33) and 34.6% had inhalation injuries. Most patients required surgery (82.7%). There were 292 cultures evaluated including blood cultures (54.8%), wound cultures (24%), and respiratory cultures (20.2%). Twenty-one patients had positive MRSA nares and the overall prevalence of MRSA infections was 17.3%. Median (IQR) time from MRSA nares to first culture was 0 days (0,1). The NPV [95% CI] of MRSA nares for all infection types was 94.7% [86.3 - 98.3%]. The PPV, sensitivity, and specificity were 50% [27.9 - 72.1%], 71.4% [42 - 90.4%], and 87.9% [78.3 - 93.7%], respectively. The NPV for culture subtypes of blood, pneumonia, and skin and soft tissue infection were 95.2% [89.4 - 98%], 93.6% [81.4 - 98.3], and 90.9% [80.6 - 96.3%], respectively.


Conclusions: The high NPV calculated in this study is consistent with previous literature, demonstrating that this test, when negative, may potentially be used to rule out MRSA in various infection types in the burn ICU population.