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

Abstract

Infection is the primary cause of death among burn-injured patients, with soft tissue infection trailing only pneumonia as the most common source of sepsis. 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. We performed a retrospective review of all 250 patients who underwent weekly nasal swab screening and developed a burn infection in our unit over a 36-month period. By comparing nasal screening results to bacterial cultures, we determined test performance metrics for MRSA nasal swabs: sensitivity 64.1%, specificity 96.2%, positive predictive value (PPV) 75.8%, and negative predictive value (NPV) 93.5%. Nasal swabs were slightly more sensitive for predicting community-acquired MRSA infections versus those that were likely hospital-acquired. 30 patients (76.9%) presented with community-acquired MRSA infections; of those, 20 (66.7%) had tested positive for MRSA colonization on nasal screen. 9 patients (23.1%) developed hospital-acquired MRSA infections; 5 (55.6%) had tested positive for MRSA on a preceding nasal swab. 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. Burn centers should employ universal MRSA nasal screening and de-escalate MRSA antibiotic coverage when treating burn infections in patients with a negative nasal swab result.