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.