Extended-Spectrum Beta-Lactamase Positivity in Infants with Febrile Urinary Tract Infection: Risk Factors, Pathogen Distribution, and Temporal Trends

Objective: To identify the risk factors for extended-spectrum beta-lactamase (ESBL) positivity in infants aged 1-12 months with febrile urinary tract infection (UTI), compare pathogen distribution and antibiotic resistance by ESBL status, and assess year-based changes in ESBL positivity from January 2018 and January 2025. Materials and Methods: This retrospective, single-center study evaluated 321 infants (1-12 months) with first febrile UTI, comparing ESBL-positive and ESBL-negative isolates and analyzing temporal trends in ESBL positivity, pathogens, and empirical antibiotic use. Results: The overall ESBL positivity rate was 57.3%. The ESBL positivity was significantly associated with urinary tract anomalies (P < .001), antibiotic exposure within the preceding 3 months (P = .003), and prophylactic antibiotic use (P = .013) on urine dipstick testing (P = .001). Pathogen distribution differed significantly between ESBL-positive and ESBL-negative groups (P < .001). Although Escherichia coli was the most common pathogen in both groups, its frequency was lower in the ESBL-positive group compared with the ESBL-negative group (57.07% vs. 79.56%), whereas Klebsiella pneumoniae and Enterobacter cloacae were significantly more frequent among ESBL-positive isolates. The ESBL-positive isolates demonstrated significantly higher resistance rates to beta-lactams, fluoroquinolones, and trimethoprim-sulfamethoxazole (all P< .001). Temporal analyses revealed significant year-to-year variation in ESBL positivity (P <.001), peaking in 2023 (90.48%). Over time, the frequency of E. coli decreased, while K. pneu moniae increased. Conclusion: Urinary tract anomalies and prior antibiotic exposure are major risk factors for ESBL-positive febrile UTI in infants. The increasing contribution of K. pneumoniae and high resistance to commonly used empirical antibiotics underscore the need to reassess empirical treatment strategies in this vulnerable population.