Reliability of Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Swab Screening for Predicting MRSA Burn Cellulitis

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) has become endemic in burn units, resulting in the frequent initiation of empiric vancomycin therapy. MRSA nasal swab screening rapidly identifies patients who are MRSA-colonized, informing contact precaution and decontamination protocols. We hypothesized that MRSA nasal swab results could also be used to reliably predict results of wound cultures obtained from infected burns.

Methods: We performed a retrospective review of all patients who underwent weekly nasal swab screening and developed a burn infection in our unit over a 36-month period.  Our institutional policy requires nasal MRSA swab screening of all patients on admission for purposes of rooming and contact precaution. The diagnostic characteristics of nasal swab screening for predicting the presence of MRSA on wound culture were calculated.

Results: 250 patients underwent MRSA nasal swab screening and were treated for burn-related infection during the study period. MRSA was detected on 13.2% of nasal swabs and in 15.6% of wound cultures. Nasal swabs had a sensitivity of 64.1%, specificity of 96.2%, positive predictive value (PPV) of 75.8%, and negative predictive value (NPV) of 93.5% for the presence of MRSA on wound culture. Nasal swabs were slightly more sensitive for predicting community-acquired MRSA infections versus those that were likely hospital-acquired.

Conclusion: The NPV calculated here indicates that patients who test negative for MRSA colonization by recent nasal swab are highly unlikely to have a burn infection caused by MRSA. A negative MRSA nasal swab on admission is a reliable indicator to de-escalate MRSA coverage when treating patients with infected burns.