Phylogeographic analysis reveals multiple international transmission events have driven the global emergence of Escherichia coli O157:H7.

Background: Shiga toxin-producing Escherchia coli O157:H7 is a zoonotic pathogen which causes numerous food and waterborne disease outbreaks. It is globally distributed but its origin and temporal sequence of geographical spread is unknown.

Methods: We analysed 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. Timed phylogeographic analysis was performed on a subset of the isolates to investigate it's 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 from Europe to Australia around 1937 (1909-1958), to USA 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 in 1975 from the USA.

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 (e.g. Holstein Friesian cattle). These findings will inform policy on action that is crucial to reduce further spread of E. coli O157:H7 and other (emerging) STEC strains globally.