Genomic Insights into a Sustained National Outbreak of Yersinia pseudotuberculosis.

In 2014, a sustained outbreak of yersiniosis due to Yersinia pseudotuberculosis occurred across all major cities in New Zealand (NZ), with a total of 220 laboratory-confirmed cases, representing one of the largest ever reported outbreaks of Y. pseudotuberculosis. Here, we performed whole genome sequencing of outbreak-associated isolates to produce the largest population analysis to date of Y. pseudotuberculosis, giving us unprecedented capacity to understand the emergence and evolution of the outbreak clone. Multivariate analysis incorporating our genomic and clinical epidemiological data strongly suggested a single point-source contamination of the food chain, with subsequent nationwide distribution of contaminated produce. We additionally uncovered significant diversity in key determinants of virulence, which we speculate may help explain the high morbidity linked to this outbreak.