Persistent Cross-species Transmission Systems Dominate Shiga Toxin-producing O157:H7 Epidemiology in a High Incidence Region: A Genomic Epidemiology Study

Several areas of the world suffer a notably high incidence of Shiga toxin-producing . To assess the impact of persistent cross-species transmission systems on the epidemiology of O157:H7 in Alberta, Canada, we sequenced and assembled O157:H7 isolates originating from collocated cattle and human populations, 2007-2015. We constructed a timed phylogeny using BEAST2 using a structured coalescent model. We then extended the tree with human isolates through 2019 to assess the long-term disease impact of locally persistent lineages. During 2007-2015, we estimated that 88.5% of human lineages arose from cattle lineages. We identified 11 persistent lineages local to Alberta, which were associated with 38.0% (95% CI 29.3%, 47.3%) of human isolates. During the later period, six locally persistent lineages continued to be associated with human illness, including 74.7% (95% CI 68.3%, 80.3%) of reported cases in 2018 and 2019. Our study identified multiple locally evolving lineages transmitted between cattle and humans persistently associated with O157:H7 illnesses for up to 13 y. Locally persistent lineages may be a principal cause of the high incidence of O157:H7 in locations such as Alberta and provide opportunities for focused control efforts.