Regional endemicity of toxigenic Vibrio parahaemolyticus lineages associated with foodborne illness in Australia

Gastrointestinal Vibrio parahaemolyticus infections, primarily associated with consumption of oysters, are emerging in Australia, where previously little was known about the disease and epidemiology. Following a multijurisdictional outbreak in 2021 and additional smaller outbreaks in subsequent years, an opportunistic whole genome sequencing study was undertaken to characterise human illness-causing strains in Australia. Through a multijurisdictional collaboration that bridged research, government, pathology service providers, aquaculture and clinicians, 676 V. parahaemolyticus genomes were contributed for analysis from human clinical, food, and environmental samples. We identified ST36, ST50 and ST417 as the dominant multi-locus sequence types causing gastrointestinal illness nationally. Phylogeographic contextualisation of Australian V. parahaemolyticus sequences within the global dataset indicates the Australian and New Zealand ST36 strain originated from a single point of introduction from the US Pacific-Northwest and is now circulating locally. In contrast, ST50 and ST417 appear to be endemic across Australia, with multiple lineages co-circulating. These findings establish a baseline for future outbreak investigations of V. parahaemolyticus in Australia and the consolidation of Australian data provides a critical platform for ongoing research, public health surveillance and risk mitigation.