Background: In 2010, the Infectious Diseases Society of America (IDSA) and the Surgical Infections Society updated recommendations for empiric therapy of hospital-associated (HA) and community-associated (CA) intra-abdominal infections (IAI). The Study for Monitoring Antimicrobial Resistance Trends (SMART) has tracked susceptibility of IAI aerobic gram-negative bacilli (GNB) globally since 2002. This report reviews susceptibility of GNB from the United States to many of the drugs recommended in the guidelines.
Methods: 22 US laboratories collected 2,866 GNB from adults with IAI in 2014-2015 (up to 100 consecutive isolates per year per lab; 1 isolate per species per patient). Susceptibility testing and determination of extended-spectrum-β-lactamase (ESBL) phenotype were done using CLSI broth microdilution methods and breakpoints. An IAI was defined as HA or CA if cultured ≥48 hours or <48 hours post-admission, respectively.
Results: The proportion of P. aeruginosa resistant to ceftazidime (CAZ) was 22.9% and 11.6% for isolates from HA and CA IAI, respectively; the proportion of ESBL+ isolates among E. coli, K. oxytoca, K. pneumoniae, and P. mirabilis was 11.9% (HA) and 7.2% (CA). Only ertapenem (ETP), imipenem (IPM), and amikacin (AMK) had susceptibility values >90% vs. HA and CA ESBL+ isolates, followed by piperacillin-tazobactam (TZP) with 69.7% (HA) and 73.8% (CA).
Susceptibility (with 95% confidence limits) of all GNB combined is shown below, using breakpoints of each species and assuming 0% susceptible if no breakpoint exists for any drug/species.
- Of the studied agents recommended for empiric therapy of HA IAI, IPM, cefepime (FEP), CAZ, TZP, and AMK were active against >80% of isolates in the US.
- However, because cephalosporins are not recommended if >20% of P. aeruginosa are resistant to CAZ or if ESBL+ Enterobacteriaceae are suspected, cephalosporins may not be appropriate for empiric therapy of HA IAI in the US.
- Furthermore, even though TZP is recommended for empiric therapy of HA IAI if ESBL+ isolates are suspected, it inhibited <70% of HA ESBL+ isolates in this study, making its empiric use questionable.
- Among drugs suggested for CA IAI, ETP, IPM, FEP, CAZ, and TZP were active against >85% of CA isolates.
K. Young, Merck & Co., Inc.: Employee , Salary
M. Motyl, Merck & Co., Inc.: Employee , Salary
D. Sahm, IHMA, Inc.: Independent Contractor , Research support