103 - Empiric Antibiotic Susceptibility Using a Traditional vs. Syndromic Antibiogram-Implications for Antimicrobial Stewardship Programs

Background: A primary tenet of antimicrobial stewardship programs (ASPs) is to establish empiric antibiotic treatment recommendations. While traditional antibiograms are useful, intrinsic variability in susceptibility exists when stratifying by source and/or location. In contrast, a syndromic antibiogram displays the likelihood of adequate coverage for a specific infection syndrome, considering the weighted incidence of pathogens causing that syndrome. The aim of the study was to compare antibiotic susceptibilities using a traditional versus syndromic antibiogram.

Methods: Between 2016-2019, 20 US institutions per year submitted up to 250 consecutive targeted gram-negative pathogens from hospitalized patients as part of the Study for Monitoring Antimicrobial Resistance Trends (SMART). MICs were determined by broth microdilution and interpreted using 2020 CLSI breakpoints, except for imipenem/relebactam (I/R) for which FDA breakpoints were used.  The traditional antibiogram included the 3 most common Gram-negative pathogens from all sources and represented critical organisms considered for empiric antibiotic coverage; the syndromic antibiogram included the 3 most commonly isolated Gram-negative pathogens from a respiratory source based on patient location.

Results: 17,561 Gram-negative isolates, including 6,654 lower respiratory isolates were evaluated.  The top 3 most common Gram-negative organisms included:  E. coli (n=6095, 44%), Klebsiella spp. (n=4097, 30%), P. aeruginosa (n=3649, 26%). Cumulative susceptibilities were comparable using a traditional vs. syndromic antibiogram (Figure 1); however, cefepime (FEP), piperacillin/tazobactam (TZP), and meropenem (MEM) susceptibilities were 5 – 8% lower when stratified by patient location (Figure 2) and ≥10% for P. aeruginosa (Figure 3).  Ceftolozane/tazobactam (C/T) and I/R demonstrated ≥90% susceptibility regardless of respiratory source or patient location.Figure 1. Cumulative susceptibility of E. coli, Klebsiella spp, and P. aeruginosa for traditional vs. syndromic antibiogram
Figure 2. Syndromic antibiogram evaluating cumulative susceptibility of E. coli (n = 637), Klebsiella spp. (n = 1190) and P. aeruginosa (n = 1997) respiratory isolates stratified by patient location
Figure 3. Syndromic antibiogram evaluating susceptibility of P. aeruginosa (n = 1997) respiratory isolates stratified by patient location


Conclusion: Our analysis demonstrated that susceptibilities were lower for first-line agents when stratified by ICU and P. aeruginosa. ASPs should consider syndromic antibiograms based on source and patient location to optimize empiric antibiotic therapy recommendations.