Impact of Nares Swabs in the Operative Management of Distal Lower Extremity Infections

Abstract

Associations between nares surveillance cultures and lower extremity wound cultures remains a topic of discussion in the literature and in clinical practice. Reports are limited due to the questionable accuracy of bedside foot cultures. A retrospective review of our institution's lower extremity wounds requiring surgical management distal to the tibial tuberosity was conducted. Deep intraoperative tissue cultures collected in a sterile operating field were referenced against nares cultures from the same hospitalization. Accuracy, sensitivity, and specificity of nares cultures for predicting methicillin-resistant Staphylococcus aureus (MRSA) infection were determined. Four hundred and forty unique patients with both nares and wound cultures met inclusion criteria. Comorbid diagnoses revealed 66.82%, 30.68%, and 32.27% of patients had diabetes mellitus, chronic kidney disease, and/or peripheral arterial disease, respectively. Sensitivity and specificity were found to be 53.13% and 96.13%, respectively. Prevalence of MRSA in a lower extremity wound was 14.9%, and accuracy of nares culture was 90.04% (CI: 86.91%-92.65%). A review of 30 false negative cases was conducted. Using exclusion criteria of a hospital admission within 60 days of presentation, history of MRSA infection, and/or presentation from a long-term care facility, negative predictive value of MRSA nares colonization was 99.51%. A case of necrotizing fasciitis accounted for one outlier. This data demonstrates that nares surveillance swabs have excellent diagnostic performance in ruling out MRSA infections in foot and ankle wounds. Further analysis is required to determine whether this performance is improved in specialized subgroups or dependent on temporal proximity.