Predictors of resistance and mortality in Klebsiella pneumoniae infections: a matched case–case–control study

Background Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major public-health threat associated with limited treatment options and increased mortality. This study identified risk factors for CRKP positive urine cultures, compared with carbapenem-susceptible K. pneumoniae positive urine cultures (CSKP), and assessed predictors of death. Methods A retrospective matched case–case–control study was conducted at a referral hospital in Najran, Saudi Arabia, between 1 January–31 December 2024. Adults with positive urine cultures of CRKP and CSKP were compared with matched controls without K. pneumoniae infection. Matching used hospital location/department, 30-day window period, specimen type, and time at risk; controls were additionally matched on age. Exploratory multivariable logistic regression identified adjusted associations. Results In exploratory adjusted models, CRKP positive urine culture episodes showed association with prolonged hospital stay/hospital settings (AOR 1.015/6.599), and several comorbidities: pulmonary disease (AOR 5.952), renal disease (AOR 3.355), and malignancy (AOR 13.420). The malignancy estimate in the CRKP vs. control model was imprecise and was treated as an exploratory signal rather than a stable adjusted predictor. Demographic predictors for CRKP included female sex (AOR 6.172) and non-Saudi nationality (AOR 7.160). Similarly, CSKP positive urine culture episodes were associated with female sex, non-Saudi nationality, renal disease; malignancy, hepatic disease (AOR 8.100) and absence of device use (AOR 9.330) produced imprecise estimates and were interpreted only as exploratory signals. When comparing CRKP to CSKP, carbapenem resistance was associated with older age (AOR 1.021), diabetes mellitus (AOR 2.689); hospital setting (AOR 36.955) estimate suggested a healthcare-associated direction but had a wide confidence interval and unstable magnitude. Mortality was higher in CRKP (18.1%) than CSKP (9.2%) and controls (9.7%), but this did not reach statistical significance in the unadjusted group comparison ( p = 0.062). The mortality model showed associations with advancing age (OR 1.038 per year), hospital setting (OR 3.852), carbapenem resistance (OR 2.844), cardiovascular disease (OR 3.302), and device utilization (OR 5.522). Conclusion CRKP was predominantly healthcare-associated and more likely among older patients and those with co-comorbidities. Since important confounders were unavailable and several estimates were imprecise, these findings should be interpreted as exploratory and hypothesis-generating.