The Changing Landscape of Urinary Tract Infections: Epidemiology, Pathogen Distribution and Antimicrobial Resistance over Six Years

Background: Urinary tract infections (UTIs) are among the most common bacterial infections worldwide and remain a major cause of antimicrobial prescribing in both community and hospital settings. Continuous epidemiological surveillance is essential to monitor changes in uropathogen distribution and antimicrobial resistance, particularly in aging populations. Methods: A retrospective observational study was conducted using urine culture data from a Portuguese tertiary healthcare network between January 2020 and December 2025. Demographic, microbiological, and antimicrobial susceptibility data were extracted from the laboratory information system. After applying predefined exclusion criteria, 44,596 positive urine cultures corresponding to distinct infectious episodes were included. Pathogen distribution, temporal trends, polymicrobial infections and antimicrobial susceptibility patterns were analyzed according to age, sex, and healthcare setting. Results: During the study period, 165,269 urine samples were processed, yielding 44,596 positive urine cultures. Women accounted for most infections, while individuals aged ≥65 years represented the largest patient group. Of all positive cultures, 41,555 (93.2%) were monomicrobial and 3041 (6.8%) were polymicrobial. Escherichia coli was the predominant uropathogen (49.6%), followed by Klebsiella pneumoniae (17.4%), Proteus mirabilis (7.0%), Enterococcus faecalis (5.3%), and Pseudomonas aeruginosa (5.1%). The overall microbiological profile remained relatively stable throughout the six-year period. Antimicrobial susceptibility testing demonstrated preserved activity of fosfomycin against the principal Enterobacterales, whereas resistance to fluoroquinolones and trimethoprim–sulfamethoxazole remained substantial. Polymicrobial infections occurred predominantly among older and hospitalized patients. Conclusions: This large-scale six-year surveillance study provides a comprehensive overview of the epidemiology of urinary tract infections within a Portuguese tertiary healthcare network. The findings confirm the continued predominance of Escherichia coli, highlight the growing burden of UTIs among older adults, and emphasize the importance of continuous local microbiological surveillance to support empirical antimicrobial therapy, antimicrobial stewardship, and future public health strategies.