Antibiotic Resistance in Urine Culture Isolates from Hospitalized Children Under Five Years with Urinary Tract Infection: A Comparison of the 2019–2020 and 2024–2025 Periods

Background/Objectives: We evaluated changes in antibiotic resistance among urine culture isolates from children under five years hospitalized with urinary tract infection (UTI) at a single center in 2019–2020 and 2024–2025. Methods: This retrospective, repeated cross-sectional study included 498 children and analyzed 359 isolates of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus spp. As second-line agents were tested selectively, primary outcomes (defined post hoc) were resistance to a core panel of agents tested in at least 90% of isolates and core-panel multidrug resistance (MDR) in Enterobacterales; other comparisons were exploratory. Fisher’s exact test, Benjamini–Hochberg correction, and adjusted Firth regression were used. Results: Second-line agents were tested mainly in cefuroxime-resistant isolates (95% vs. 7% for ceftazidime in E. coli), biasing resistance estimates. In the core panel, no difference was significant in E. coli, and the decrease in cefuroxime resistance in K. pneumoniae did not survive correction. Core-panel MDR was lower in 2024–2025 (51.9% vs. 38.7%; p = 0.019; adjusted OR 0.56, 95% CI 0.35–0.88); full-category MDR was not (68.4% vs. 58.3%; p = 0.067). Conclusions: Differences may reflect testing practices and case mix rather than true changes in resistance. Findings apply only to hospitalized children under five years at this center and require confirmation.