1560 - Microbiology of Necrotizing Fasciitis and Implications on Antimicrobial Stewardship

Background: Necrotizing fasciitis (NF) is a rare but deadly soft tissue infection. Early diagnosis, antibiotics, and surgical management are critical in treatment. Current IDSA guidelines recommend broad empiric antibiotics (eg, vancomycin + piperacillin-tazobactam or a carbapenem). At our institution, this invariably consists of empiric treatment for methicillin-resistant Staphylococcus aureus (MRSA) and resistant gram-negative organisms (eg, Pseudomonas aeruginosa), usually with piperacillin-tazobactam. Clindamycin is the common third agent used empirically; however, the literature supports use of clindamycin only in confirmed cases of Group A Streptococcus (GAS). With the increasing dangers of antibiotic resistance, use of such broad agents may not be necessary for NF. We evaluated the microbiology of NF and the implications on empiric antibiotic treatment.

Methods: Retrospective chart review of adults (≥18 years) with a diagnosis of NF from January 2016 to May 2020.

Results: Twenty-five cases of NF in 22 patients were recorded. The median age was 54.5 (IQR 37-59.8) and 15 (60%) were male. On presentation, 24 (96%) met systemic inflammatory response syndrome criteria with a median laboratory risk indicator for necrotizing fasciitis score of 15 (IQR 9-31.3, n = 20). The median presenting white blood cell count was 17.5 x 103 cells/uL (IQR 13.5-25.2), median C-reactive protein was 321.6 mg/L (IQR 25.9-37.6) and median creatinine was 1.2 mg/dL (IQR 0.7-1.6). The most frequently isolated organisms were anaerobes (n=9, 36%) and Streptococci other than GAS (n = 9, 36%). GAS was isolated in 6 patients (24%) and S. aureus in 2 patients (8%). All cases of S. aureus were methicillin-susceptible. No Pseudomonas species (PsA) or extended-spectrum beta-lactamase (ESBL) gram negative organisms were isolated. Three patients (12%) had no organisms isolated from surgical cultures. Seven patients (28%) had positive blood cultures. Of the empiric antibiotics used, 24 (96%) patients were exposed to clindamycin and an anti-pseudomonal antibiotic.

Conclusion: Empiric treatment of PsA and ESBL organisms is not necessary in NF. This infection should be considered a priority target for antimicrobial stewardship to reduce prescribing of broad-spectrum antibiotics to empirically treat these organisms.