Integrating Epidemiological Investigation and Whole-Genome Sequencing to Evaluate Suspected Healthcare-Associated Transmission of the Corynebacterium jeikeium Complex

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Abstract
Routine identification of Corynebacterium species can be challenging and may complicate investigation of suspected healthcare-associated transmission. We investigated a suspected cluster of blood culture isolates routinely identified as Corynebacterium jeikeium and retrospectively evaluated similarly identified isolates recovered at our hospital. After three patients in a hematology ward had blood cultures yielding C. jeikeium within approximately one month in 2024, pulsed-field gel electrophoresis (PFGE), environmental sampling, and follow-up surveillance were performed. We subsequently reviewed all blood culture isolates routinely identified as C. jeikeium from 2019 to 2025. Ten isolates from 10 unique patients underwent long-read whole-genome sequencing (WGS). Species identity was assessed by average nucleotide identity (ANI) against type-strain genomes, and genomic relatedness by core-genome phylogenetic and pairwise genome analyses. PFGE showed indistinguishable patterns for two cluster-associated isolates. No environmental isolate was identified as Corynebacterium spp., and no additional temporally associated cases were detected. WGS identified all 10 isolates as C. macclintockiae and did not support a single-clone transmission event; the two isolates with indistinguishable PFGE patterns were closely related but not genomically identical. However, direct or indirect transmission between the corresponding patients could not be excluded. These findings support integrating epidemiological investigation, accurate species identification, and high-resolution genomic analysis when evaluating suspected healthcare-associated transmission involving members of the C. jeikeium complex.

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