Invasive Infection Caused by a Hypervirulent ST367-KL1 <i>Klebsiella quasipneumoniae</i> subsp. <i>similipneumoniae</i>: First Case Report in Japan

Klebsiella quasipneumoniae is a member of the Klebsiella pneumoniae complex that is difficult to distinguish from K. pneumoniae using conventional laboratory methods, and information on its clinical manifestations is limited. We describe the first known case of invasive infection with hypervirulent K. quasipneumoniae subsp. similipneumoniae in Japan. A 65-year-old woman with pancreatogenic diabetes mellitus presented with fever and nausea. Computed tomography revealed a liver abscess and multiple pulmonary nodules with cavitation suggestive of septic pulmonary emboli. Blood cultures yielded an isolate identified as K. pneumoniae complex. Whole-genome sequencing (WGS) subsequently identified the isolate as K. quasipneumoniae subsp. similipneumoniae, sequence type 367 (ST367) and capsular type K1 (KL1). The isolate exhibited a hypermucoviscous phenotype and harbored the virulence-associated genes iroBCDN, iucABCD/iutA, rmpA/A2, and peg-344. The patient improved following antimicrobial therapy with meropenem for 10 days, followed by cefmetazole for 13 days, and was discharged home after a hospital stay of 81 days. This case highlights the potential for invasive infection caused by hypervirulent K. quasipneumoniae, the usefulness of WGS for species identification, and the need for ongoing clinical and genomic surveillance to monitor the emergence of this pathogen.