Investigators analyzed 207 episodes of Klebsiella pneumoniae bloodstream infection collected at a single tertiary center in Japan from 2022 through 2024. They applied a genotypic case definition of hypervirulence that required PCR positivity for all five markers: rmpA, rmpA2, iucA, iroB, and peg-344. The laboratory workflow screened first for rmpA and then tested rmpA-positive isolates for the remaining markers; isolates that did not meet the five-marker threshold were classified as classical K. pneumoniae (cKp). The study began with 290 first episodes within the species complex but excluded non–K. pneumoniae species identified by PCR and episodes lacking usable isolates or clinical data, yielding 207 episodes for clinical analysis. Whole-genome sequencing was performed on a subset of isolates using an enriched sampling strategy that included all hvKp isolates, isolates with 1–4 biomarkers, all third-generation cephalosporin–resistant isolates, and a random sample of cKp isolates.
Data indicated that hvKp, defined by the five biomarkers, accounted for 14% (28/207) of bloodstream infection episodes. Abscess complications were substantially more frequent among hvKp episodes: imaging-confirmed abscesses occurred in 61% (17/28) of hvKp cases versus 13% (23/179) of cKp cases. The cohort showed longer resource use associated with hvKp: median post–disease onset length of stay was 28 days for hvKp case-patients compared with 14 days for those with cKp, and total duration of antimicrobial therapy was a median 43 days versus 14 days, respectively. The investigators recorded 30-day mortality as a secondary endpoint; the source reported objectives and outcomes but did not provide additional, granular mortality figures in the abstract. Abscesses and other metastatic infections were defined strictly by imaging confirmation; the study excluded clinically suspected but nonimaged abscesses from the abscess outcome count.
Short-read whole-genome sequencing identified CTX-M–type extended-spectrum β-lactamase genes in 11% (3/28) of hvKp isolates. Those three hvKp isolates corresponded to 1.4% (3/207) of all K. pneumoniae bloodstream infection episodes in the analyzed cohort. The sequencing strategy was intentionally enriched, and the authors reported these genomic resistance findings within that sampling frame. The study classified third-generation cephalosporin resistance (3GCR) phenotypically as nonsusceptibility to ceftriaxone and defined multidrug resistance as nonsusceptibility to more than one agent in over three antimicrobial categories, following referenced standards. Antimicrobial susceptibility testing was performed by broth microdilution and interpreted by Clinical and Laboratory Standards Institute criteria; the source lists the full antimicrobial panel used in susceptibility testing.
The study team observed that most sequence type 23 (ST23) hvKp episodes involved abscesses: 9 of 10 ST23 hvKp episodes had abscess complications. Investigators summarized lineage-specific genomic features for hvKp isolates and assessed the degree to which hypervirulence markers co-occurred with antimicrobial-resistance determinants. The report presents these lineage associations as part of its genomic characterization; further details, including phylogenetic analyses and full sequencing methods, are provided in the article appendix and associated figures and tables.
Clinical and microbiologic data came from electronic medical records and laboratory systems at the Kameda Medical Center. Blood cultures were processed with a BD BACTEC FX system and species identification was performed by MALDI-TOF mass spectrometry. The PCR assays and primer sequences used for screening the five biomarkers are described in previously published methods and summarized in the article Appendix. The hvKp classification was assigned retrospectively for analysis and was not available to treating clinicians during routine care. Abscess outcomes were restricted to imaging-confirmed lesions; clinically suspected but nonimaged abscesses were not counted.
The authors acknowledged limitations inherent to a single-center, retrospective design and to the enriched sequencing sampling strategy, which affects prevalence estimates derived from genomic subgroups. They also noted that species-level exclusions (K. variicola and K. quasipneumoniae) reduced the analytic denominator to 207 K. pneumoniae episodes. Methodological specifics such as PCR primer sequences, sequencing pipelines, and full susceptibility tables appear in the appendix and figures that accompany the article. The dataset showed that the five-biomarker definition delineated a clinically distinct subgroup of bloodstream infections characterized by higher abscess frequency and increased durations of hospitalization and antimicrobial therapy, and that a small proportion of hvKp isolates carried CTX-M–type extended-spectrum β-lactamase genes.