BackgroundRapid and accurate identification of Verotoxigenic Escherichia coli (VTEC) O157:H7 is dependent on well-established, standardized and highly discriminatory typing methods. Currently, conventional subtyping tests for foodborne bacterial pathogen surveillance are rapidly being replaced with whole-genome sequencing (WGS) in public health laboratories. The capacity of WGS to revolutionize global foodborne disease surveillance has positioned this tool to become the new gold standard; however, to ensure evidence standards for public health decision making can still be achieved, the performance of WGS must be thoroughly validated against current gold standard methods prior to implementation. Here we aim to verify the performance of WGS in comparison to pulsed-field gel electrophoresis (PFGE) and multiple-locus variable-number tandem repeat analysis (MLVA) for eight retrospective outbreaks of VTEC O157:H7 from the Canadian perspective. Since real-time implementation and routine use of WGS in public health laboratories is highly reliant on standardized data analysis tools, we also provide a comparative analysis of two popular methodologies for WGS analyses; an in-house developed single nucleotide variant phylogenomics (SNVPhyl) pipeline and the BioNumerics whole genome multilocus sequence typing (wgMLST) tool. To provide a useful and consistent starting point for examining laboratory-based surveillance data for VTEC O157:H7 in Canada, we also aim to describe the number of genetic differences observed among outbreak-associated isolates.ResultsWGS provided enhanced resolution over traditional subtyping methods, and accurately distinguished outbreak-related isolates from non-outbreak related isolates with high epidemiological concordance. WGS also illuminated potential linkages between sporadic cases of illness and contaminated food, and isolates spanning multiple years. The topologies generated by SNVPhyl and wgMLST were highly congruent with strong statistical support. Few genetic differences were observed among outbreak-related isolates (≤5 SNVs/ < 10 wgMLST alleles) unless the outbreak was suspected to be multi-strain.ConclusionsThis study validates the superiority of WGS and indicates the BioNumerics wgMLST schema is suitable for surveillance and cluster detection of VTEC O157:H7. These findings will provide a useful and consistent starting point for examining WGS data for prospective laboratory-based surveillance of VTEC O157:H7, but however, the data will continue to be interpreted according to context and in combination with epidemiological and food safety evidence to inform public-health decision making in Canada.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5243-3) contains supplementary material, which is available to authorized users.

Objectives:Are Canadians who study abroad (CSAs) more likely to stay in Canada than other international medical graduates (IMGs)? We looked at retention patterns of CSAs and immigrant IMGs who completed post-graduate medical education (PGME) training in Canada to describe the proportion and predictors of those working in Canada and in rural communities in Canada in 2015.Methods:We linked the National IMG Database to Scott's Medical Database to track the work locations of CSAs and immigrant IMGs in 2015.Results:Of the 1,214 IMGs who entered PGME training in Canada between 2005 and 2011, most were working in Canada in 2015 (88.0%). Relatively few IMGs worked in rural communities (9.1%). There were no differences in work location patterns of CSAs and immigrant IMGs.Conclusion:Contrary to what CSA advocates suggest, CSAs have the same retention patterns as immigrant IMGs. PGME admission policies should treat all IMGs in the same manner, regardless of their citizenship or residency before medical school.

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