Eleven-year surveillance of Pseudomonas aeruginosa infections and antimicrobial resistance trends in a Portuguese tertiary hospital, 2014 - 2024: Trends and insights into novel agents.

Abstract

Pseudomonas aeruginosa is a frequent hospital-associated pathogen, often causing severe infections with limited treatment options due to increasing prevalence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains. This study evaluated its prevalence and resistance patterns in a large tertiary hospital. A retrospective observational study analysed all P. aeruginosa clinical isolates collected over 11 years (2014-2024) from inpatients and outpatients. Antimicrobial susceptibility testing included carbapenems, cephalosporins, piperacillin-tazobactam, aztreonam, aminoglycosides, ciprofloxacin, fosfomycin, colistin, ceftolozane-tazobactam and ceftazidime-avibactam. A total of 22883 P. aeruginosa isolates were analysed, representing 16802 episodes from 9978 patients. Mean patient age was 60.9 ±24.7 years, with male predominance. The prevalence of P. aeruginosa among hospitalized patients was 3.0%. Overall, 11.9% of isolates were MDR, 3.3% XDR and 84.8% non-MDR, with MDR and XDR rates increasing over time (p<0.05). A difficult-to-treat phenotype was present in 4.2%. Resistance to at least one carbapenem was observed in 19.0% of isolates, and to ciprofloxacin in 20.3%. Susceptibility to piperacillin-tazobactam, meropenem, ceftazidime, and amikacin remained above 80%. Most isolates non-susceptible to piperacillin-tazobactam or ceftazidime remained susceptible to amikacin, supporting amikacin-containing combination regimens in high-risk settings. Colistin resistance remained below 1%. Among MDR isolates, susceptibility to ceftazidime-avibactam decreased between 2017 and 2024 (100.0% to 83.7%, p<0.05), whereas ceftolozane-tazobactam susceptibility fluctuated over time (83.1% to 88.2%, p<0.05). These findings reveal a shifting resistance landscape and underscore the need for sustained surveillance, antimicrobial stewardship, and updated empirical treatment strategies, while highlighting a critical gap in contemporary epidemiological data.