Urinary tract infections caused by Gram-negative bacteria in elderly hospitalized patients: Epidemiology, clinical features and outcomes in the era of antimicrobial resistance

Objective: Urinary tract infections (UTI) are among the most common infections in elderly hospitalized patients, often caused by multi-drug resistant (MDR) organisms and characterized by poor clinical outcomes. This study aimed to evaluate the clinical characteristics, microbiology, treatment patterns, and predictors of mortality in elderly hospitalized patients with UTI, with a focus on infections caused by MDR Gram-negative bacteria (MDR-GNB). Methods: A retrospective analysis was conducted on 171 patients hospitalized between January 2022 and December 2023 at a large academic hospital in Siena, Italy. Data on demographics, comorbidities, infection characteristics, antimicrobial resistance, treatments, and outcomes were collected. Risk factors for MDR-GNB UTI and predictors of 14-d mortality were identified through univariable and multivariable analyses. Results: Of 171 patients (median age: 82 y), 106 (62.0%) had a catheter-associated UTI, and 105 (61.4%) had a healthcare-associated UTI. MDR-GNB were isolated in 68.4% of cases. Common pathogens included Escherichia coli (74/171, 43.3%), Klebsiella spp. (39/171, 22.8%) and Pseudomonas aeruginosa (33/171, 19.3%). Among Enterobacterales 35.1% were Extended-spectrum β-lactamases-producers, 3.7% carried Klebsiella pneumoniae carbapenemase, and 3.0% metallo-β-lactamases. Overall, the 14-d mortality rate was 12.9%. Predictors of 14-d mortality included septic shock, infections caused by Providencia stuartii, infections caused by New Delhi metallo-β-lactamase-producing K. pneumoniae, and inappropriate empirical antibiotic therapy. Conclusions: UTI significantly affect hospital length of stay and mortality in elderly patients. In the current context, resistance mechanisms including K. pneumoniae carbapenemase and metallo-β-lactamases production, must be considered when managing these infections. Prompt recognition of risk factors for infections caused by MDR organisms and optimized antimicrobial strategies are essential to improve outcomes in this vulnerable population.