Klebsiella pneumoniae is associated with increased mortality versus Escherichia coli in carbapenem-susceptible Enterobacterales bacteraemia: a Peruvian cohort

Objectives To identify predictors of all-cause 30-day mortality in bloodstream infections (BSI) caused by carbapenem-susceptible Escherichia coli and Klebsiella pneumoniae, with emphasis on bacterial species and the extended-spectrum β-lactamase (ESBL) phenotype. Methods This was a single-centre retrospective cohort study of adults with a first episode of BSI due to carbapenem-susceptible E. coli or K. pneumoniae at a referral hospital in Lima, Peru (June 2020–December 2023). Primary outcome: All-cause 30-day mortality. A multivariable Cox model was built, with covariate selection guided by a directed acyclic graph, and the species × ESBL interaction was tested. Results Of the 403 patients (median age 66 years, 55.8% men; 58.6% ESBL+), 83 (20.6%) died. Mortality was higher in patients with K. pneumoniae than in those with E. coli (26.8% versus 17.4%; log-rank P = 0.018). In the multivariable analysis, K. pneumoniae was an independent predictor [adjusted HR (aHR) 1.72; 95% CI, 1.09–2.73; P = 0.021], as was a Charlson score ≥6 (aHR 8.43; 95% CI, 3.33–21.3; P < 0.001). ESBL was not an independent predictor (aHR 1.45; 95% CI, 0.92–2.29; P = 0.113), nor was the species × ESBL interaction (P = 0.43). The effect of K. pneumoniae was consistent across all sensitivity analyses (aHR 1.66–1.94). Conclusions K. pneumoniae nearly doubled mortality compared with E. coli, independently of ESBL, which did not predict mortality in this cohort of carbapenem-susceptible isolates. These findings challenge the assumption of prognostic homogeneity within carbapenem-susceptible Enterobacterales and support species stratification.