Lessons from 5 Years of Routine Whole-Genome Sequencing for Epidemiologic Surveillance of Shiga Toxin–Producing Escherichia coli, France, 2018–2022

Abstract

Whole-genome sequencing (WGS) is routine for surveillance of Shiga toxin–producing Escherichia coli human isolates in France. Protocols use EnteroBase hierarchical clustering at <5 allelic differences (HC5) as screening for cluster detection. We assessed current implementation after 5 years for 1,002 sequenced isolates. From genomic distances of serotypes O26:H11, O157:H7, O80:H2, and O103:H2, we determined statistical thresholds for cluster determination and compared those with HC5 clusters. Thresholds varied by serotype, 5–16 allelic distances and 15–20 single-nucleotide polymorphisms, showing limits of a single-threshold approach. We confirmed validity of HC5 screening for 3 serotypes because statistical thresholds had limited effect on isolate clustering (high sensitivity and specificity). For O80:H2, results suggest that HC5 is less reliable, and other approaches should be explored. Public health officials should regularly assess WGS used for Shiga toxin–producing E. coli surveillance to account for serotype and genomic evolution and to interpret WGS-linked isolates in light of epidemiologic data.