Antimicrobial Activity of Aztreonam-Avibactam and Other β-Lactamase Inhibitor Combinations Tested Against Enterobacterales Isolates from Pediatric Patients from United States Medical Centers (2019–2023)

<b>Objective:</b> To evaluate the antimicrobial susceptibility of Enterobacterales isolated from pediatric patients. <b>Methods:</b> A total of 5723 isolates were consecutively collected (1/patient) from pediatric patients (<18 years old [yo]) from 82 United States medical centers in 2019-2023 and susceptibility-tested by broth microdilution method. Susceptibility was stratified by infection type and patient age: ≤1 yo (<i>n</i> = 2275), 2-5 yo (<i>n</i> = 1130), 6-12 yo (<i>n</i> = 1213), and 13-17 yo (<i>n</i> = 1105) and compared to adults (18-64 yo; <i>n</i> = 17,712). <b>Results:</b> Pediatric isolates were mainly from pneumonia (21.8%), bloodstream (BSI; 15.3%), and urinary tract infection (UTI; 51.8%). Aztreonam-avibactam, ceftazidime-avibactam, and meropenem-vaborbactam were active against ≥99.4% of ceftriaxone-nonsusceptible (99.4-100.0% susceptible), multidrug-resistant (MDR; 99.7-100.0% susceptible), and ESBL producer (99.7-100.0% susceptible) isolates from pediatric patients. Susceptibility to imipenem-relebactam varied from 97.1% (ceftriaxone-nonsusceptible) to 100.0% (ESBL producers). Ceftolozane-tazobactam showed good activity against ESBL producers (91.8% susceptible), but limited activity against ceftriaxone-nonsusceptible (75.8% susceptible) and MDR isolates (80.9% susceptible). The MDR phenotype varied from 14.3% (13-17 yo) to 19.7% (6-12 yo) among pediatric isolates (15.8% overall) and was 20.7% among adult Enterobacterales. Carbapenem resistance rates were markedly lower in pediatric (0.1%) isolates compared to adult isolates (1.3%). The ESBL profiles were similar among pediatric and adult isolates; 90.1% of ESBL producers from pediatric patients and 88.5% from adults carried a CTX-M +/- an OXA-1/30 gene. <b>Conclusions:</b> Antimicrobial resistance was generally lower among Enterobacterales from pediatric patients compared to adults. ESBL-producing Enterobacterales, mainly CTX-M, remain an important cause of infection in children. Aztreonam-avibactam, ceftazidime-avibactam, and meropenem-vaborbactam were highly active against isolates from both pediatric and adult population.