Prevalence and features of hypervirulent in respiratory specimens at a US hospital system.

Hypervirulent (hvKp) strains are considered to be relatively rare in the United States, but cases are increasingly reported. We prospectively and serially collected clinical isolates identified in respiratory specimens at a health system in Western Pennsylvania between 2020 and 2022. A total of 273 . isolates from 216 unique patients were analyzed for markers of hypervirulence by both string test for a hypermucoid phenotype and multiplex PCR to detect isolates carrying cardinal virulence genes , , , and . Of the 273 isolates, 13 (4.8%) tested positive by string test including 11 nonduplicate isolates, and two of these (0.7%) were positive by PCR for virulence genes , , , and . The latter two putative hvKp strains, belonging to sequence types ST23-K1 and ST86-SLV-K2, possessed pLVPK-like plasmids, and were collected from community-associated infections in individuals without known travel histories. Both putative hvKp strains and two additional string test-positive strains were resistant to killing by human serum. The hvKp strains caused significant pneumonia in mice infected by oropharyngeal aspiration, with significantly higher weight loss and increased bacterial burden in the lungs of mice infected with the KL1 (ST23) strain compared to the KL2 (ST86-SLV) strain. We also observed decreased survival of mice infected with the KL1 strain compared to the KL2 strain. These findings add to the growing body of evidence suggesting that hvKp strains, once considered endemic to Asia, may now be circulating in North America.IMPORTANCECertain lineages of are increasingly recognized to cause severe community-associated infection, but information on their prevalence in the United States is limited. In a prospective, sequential cohort of 273 . respiratory isolates, we identified two of them as genetically defined hypervirulent . The isolates were from local residents who developed community-onset pneumonia, suggesting that hypervirulent may already be present in the community.