O43 – Predictors of Monomicrobial Necrotizing Fasciitis
Author(s):
Background: Broad-spectrum antibiotic therapy is a cornerstone in the management of necrotizing fasciitis in the emergent setting. Clindamycin is often included empirically to cover monomicrobial Gram-positive pathogens, but is associated with significant side effects, including the induction of Clostridium difficile colitis. However, there have been no studies predicting monomicrobial infections prior to obtaining cultures. The purpose of this study was to identify independent predictors of monomicrobial necrotizing fasciitis in order to avoid the use of clindamycin where unnecessary.
Hypothesis: We hypothesized that monomicrobial infections are characterized by involvement of the upper extremities and fewer comorbid diseases.
Methods: We reviewed all cases of potential necrotizing soft tissue infection occurring between 1996 and 2013 in a single tertiary care center. Necrotizing fasciitis was defined as rapidly progressing necrotic fascia upon debridement with positive tissue cultures. Univariate analysis was performed using T-test, Wilcoxon rank sum, Chi-sq., and Fisher’s exact test where appropriate. Multivariate logistic regression was used to identify independent variables associated with the outcome.
Results: 151 patients with confirmed necrotizing soft tissue infections with complete data sets were used for this study. Of the monomicrobial infections, 61.8% were Group A streptococci, 20.1% S. aureus and 12.7% E. coli. Of the polymicrobial infections, E. coli was involved 13.7% of the time, followed by Candida species 12.9%, and B. fragilis 11.3%. On univariate analysis, immunosuppression, upper extremity infection, and initial serum sodium were associated with monomicrobial infection, while morbid obesity and perineum infection site were associated with polymicrobial infection. On multivariate analysis, the strongest predictor of monomicrobial infection was immunosuppression (OR: 7.00 95% CI 2.198-22.32) followed by initial serum sodium (OR: 1.1, 95% CI 1.032-1.236). Morbid obesity (OR: 0.055, 95% CI 0.007-0.45) and perineum infection site (OR: 0.32, 95% CI 0.134-0.765) were independently associated with polymicrobial infection. C-statistic for the model = 0.819.
Conclusions: We identified independent risk factors associated with monomicrobial necrotizing fasciitis. We suggest empiric clindamycin coverage could potentially be limited to patients who are immunosuppressed, have an elevated serum sodium, or with upper extremity involvement.