Characterisation and risk-factor profiling of P. aeruginosa urinary tract infections: pinpointing those likely to be caused by multidrug-resistant strains

Objectives: To characterise urinary tract infections (UTIs) caused by Pseudomonas aeruginosa in hospitalised adults and identify risk factors for those caused by multidrug-resistant (MDR) strains. Methods: A retrospective case-case-control study was conducted in two teaching hospitals. Results: 242 monomicrobial P. aeruginosa UTIs were analysed, 65 (26.8%) of which were caused by MDR strains. Clinical treatment failure at 72 h was more frequent in MDR cases (38/65 [58.4%] vs. 45/177 (25.4%) in non-MDR cases, p=<0.001), particularly when a β-lactam-β-lactamase inhibitor combination or fluoroquinolone was initially prescribed. By day 7 (when all treatment regimens were consistent with antimicrobial susceptibility testing (AST) results), treatment failure rates were similar (MDR 15/65 [23.1%] vs. non-MDR 25/177 [14.1%], p=0.09). In-hospital mortality rates remained low in both groups (6/65 [9.2%] vs. 22/177 (12.3%), p=0.49), but median hospital stays for the MDR cases were longer (48 vs. 22 days in non-MDR, p=<0.001). The models for predicting MDR and non-MDR P. aeruginosa UTIs displayed good discriminatory power. The presence of ≥3 risk factors for MDR P. aeruginosa UTI was associated with an OR for this outcome of 7.44 (95% CI 3,24-17.57, P<0.001; specificity 91%, accuracy 75%). The model for predicting non-MDR P. aeruginosa UTI displayed similar accuracy (74%) with a risk-factor burden threshold of ≥2 (OR 7.02 [95% CI 4.61-10.70], P<0.001). Conclusions: Risk-factor assessment can identify UTIs in hospitalised patients likely to be caused by MDR P. aeruginosa strains, thereby facilitating targeted infection-control and timelier, effective treatment of these infections.