Predictors of Methicillin-Resistant Staphylococcus Aureus in Necrotizing Soft Tissue Infections

Authors:
Anahita Jalilvand, Bradley Butsch, Courtney Collins, George Abboud, Jonathan Wisler, Patrick Quinn, Shachi Srivatsa

Body of Abstract:
Background: Management of necrotizing soft tissue infections (NSTI) consists of emergent surgical debridement and broad-spectrum antibiotic treatment. Methicillin-resistant staphylococcus aureus (MRSA) is one of the few resistant organisms frequently covered empirically. In this study, we aim to better assess the prevalence, outcomes, and predictors associated with MRSA-positive NSTIs.

Methods: A retrospective analysis of institutional data for patients diagnosed with NSTIs was identified (n = 634; 2011-2023). Outcomes of interest included mortality, length of stay, intensive care requirements, acute kidney injury (AKI), discharge destination, and 30-day readmission. Outcomes were examined based on whether the patient’s wound culture grew MRSA or not. Characteristics collected for each patient included demographics, comorbidities, micro-organisms, and index hospitalization data. Significant predictors of MRSA infection were identified using logistic regression.

Results: Of 634 patients, 77 (12.3%) grew MRSA-positive wound cultures, and 557 (89.2%) did not. The MRSA-positive cohort had higher incidences of liver disease (19.5% vs. 7.5%, p=0.001) and intravenous drug use (24.7% vs. 8.6%, p<0.001). Bacteremia was more prevalent in the MRSA-positive cohort (29.9% vs 15.6%, p = 0.003). MRSA-positive infections were more likely in upper limbs (19.7%), lower limbs (16.3%), and head/neck NSTIs (15.8%) and least likely in groin NSTIs (5.2%, p < 0.001). Groin infection was an independent negative predictor of having MRSA-positive cultures (odds ratio 0.35, 95% CI 0.17-0.71, p = 0.004). There was no difference between cohorts in in-hospital mortality, 90-day mortality, length of stay, amputation, debridement number, acute kidney injury, or discharge disposition. There was a higher rate of 30-day hospital readmission (32.5% vs 21.4%, p = 0.042) in the MRSA-positive cohort. Conclusion: Patients with MRSA-positive wound cultures were more likely to have bacteremia and had higher rates of 30-day readmission. Groin NSTIs were significantly less likely to grow MRSA than other NSTI locations.