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Conclusions

While many questions remain to be answered regarding the factors defining VTEC of public health concern, the best information available at this time indicates a possible way forward in assessing food-borne VTEC isolates for food safety purposes.

  • The current best definition of VTEC of public health concern at this time includes, but is not limited to, the presence of key virulence markers including all VT1 and VT2 variants, key adhesion genes such as eae and/or aggR (and/or possibly others, which will need to be clearly defined).
  • Food testing methods should be able to rapidly discriminate O157:H7 VTEC from non-O157 VTEC as the former is immediately actionable on primary identification, while the latter may be comprehensively characterized by high-capacity techniques including (but not limited to) WGS analyses to determine the serotype, VT subtypes, sequence type, and other salient features which need to be considered in conjunction with other relevant information linked to the risk assessment process. Notwithstanding, it is important to understand and consider the limitations of NGS technology in interpreting results.
  • VTEC are a complex family of pathogens created through the transfer of mobile genetic elements. There is significant variability in the presence of specific virulence factors in individual strains of VTEC, so each isolate needs to be assessed on a "case-by-case" basis to determine its food safety significance. Such assessments may include consideration of all the pertinent factors described in this document.
  • The scope of analysis and decision-making should not be limited to specific serogroups , since Canadian public health data show that infections with diverse serotypes may occur, often with strains falling outside the currently defined "big seven" group of "priority" VTEC identified on the basis of US epidemiological data.
  • More information is needed to clarify the role of different virulence genes and genetic variations reported in the literature, and there is a need to continue documenting WGS data for food and clinical VTEC isolates for information gathering to guide future refinements in the identification of VTEC of health concern and the attendant test approaches.
  • Next generation sequencing genomics technologies are well suited for the analysis of food and clinical isolates in determining their salient characteristics for risk management purposes.


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