"Risk of death in Klebsiella pneumoniae bloodstream infections is associated with specific phylogenetic lineages.".

BACKGROUND: Klebsiella pneumoniae species complex (KpSC) bloodstream infections (BSIs) are associated with considerable morbidity and mortality, particularly in elderly and multimorbid patients. Multidrug resistant (MDR) strains have been associated with poorer outcome. However, the clinical impact of KpSC phylogenetic lineages on BSI outcome is unclear.

METHODS: In an 18-month nationwide Norwegian prospective study of KpSC BSI episodes in adults, we used whole genome sequencing to describe the molecular epidemiology of KpSC, and multivariable Cox regression analysis including clinical data to determine adjusted hazard ratios (aHR) for death associated with specific genomic lineages.

FINDINGS: We included 1078 BSI episodes and 1082 bacterial isolates from 1055 patients. The overall 30-day case-fatality rate (CFR) was 12.5%. Median patient age was 73.4, 61.7% of patients were male. Median Charlson comorbidity score was 3. Klebsiella pneumoniae sensu stricto (Kp) (79.3%, n=858/1082) and K. variicola (15.7%, n=170/1082) were the dominating phylogroups. Global MDR-associated Kp clonal groups (CGs) were prevalent (25.0%, n=270/1082) but 78.9% (n=213/270) were not MDR, and 53.7% (n=145/270) were community acquired. The major findings were increased risk for death within 30 days in monomicrobial BSIs caused by K. variicola (CFR 16.9%, n=21; aHR 1.86, CI 1.10-3.17, p=0.02), and global MDR-associated Kp CGs (CFR 17.0%, n=36; aHR 1.52, CI 0.98-2.38, p=0.06) compared to Kp CGs not associated with MDR (CFR 10.1%, n=46).

CONCLUSION: Bacterial traits, beyond antimicrobial resistance, have a major impact on the clinical outcome of KpSC BSIs. The global spread of MDR-associated Kp CGs is driven by other mechanisms than antibiotic selection alone. Further insights into virulence determinants, and their association with phylogenetic lineages are needed to better understand the epidemiology of KpSC infection and clinical outcome.