Background: Shiga toxin-producing Escherchia coli (STEC) O157:H7 is a zoonotic pathogen that causes numerous food and waterborne disease outbreaks. It is globally distributed, but its origin and the temporal sequence of its geographical spread are unknown. Methods: We analyzed whole-genome sequencing data of 757 isolates from 4 continents, and performed a pan-genome analysis to identify the core genome and, from this, extracted single-nucleotide polymorphisms. A timed phylogeographic analysis was performed on a subset of the isolates to investigate its worldwide spread. Results: The common ancestor of this set of isolates occurred around 1890 (1845-1925) and originated from the Netherlands. Phylogeographic analysis identified 34 major transmission events. The earliest were predominantly intercontinental, moving from Europe to Australia around 1937 (1909-1958), to the United States in 1941 (1921-1962), to Canada in 1960 (1943-1979), and from Australia to New Zealand in 1966 (1943-1982). This pre-dates the first reported human case of E. coli O157:H7, which was in 1975 from the United States. Conclusions: Inter- and intra-continental transmission events have resulted in the current international distribution of E. coli O157:H7, and it is likely that these events were facilitated by animal movements (eg, Holstein Friesian cattle). These findings will inform policy on action that is crucial to reduce the further spread of E. coli O157:H7 and other (emerging) STEC strains globally.
Bibliographical noteFunding Information:
This work was supported by Food Standards Scotland (grant number FS102029) and the University of Aberdeen, the New Zealand Institute of Environmental Science and Research, the Public Health Agency of Canada, and the USDA. New Zealand clinical isolates were provided by the Institute of Environmental Science and Research, funded by the Ministry of Health. The authors thank Food Standards Scotland (FS102029) for support and the University of Aberdeen for funding sequencing of the Scottish E. coli O157:H7 genomes. They thank the Public Health Agency of Canada for the sequencing of Canadian E. coli O157:H7 genomes. The authors thank the Canadian National Enteric Surveillance Program (NESP) of the Public Health Agency of Canada for providing national incidence rates of E. coli O157:H7 infection in Canada, specifically, Frank Pollari and Kimberly Nguy from the Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, and the Enteric Diseases Program of the National Microbiology Laboratory. They also thank the provincial public health laboratories for providing this information to the NESP. They thank Adrian Cookson for the sequencing of New Zealand E. coli O157:H7 genomes and epidemiological data for human cases and for help and advice with the New Zealand isolates. They thank Springer Browne from Massey University for providing New Zealand cattle import data. They thank the Public Health Microbiology Laboratory, Queensland Department of Health, for the provision of Queensland human isolates.
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