Summary

The Enteric Reference Laboratory (ERL) typed a total of 755 Yersinia isolates in 2025 including 7 Y. pseudotuberculosis with the remainder typed as Y. enterocolitica (748/755, 99.1%). The most common type for Y. enterocolitica was biotype 2/3 serotype O:9 (reported as its genomic equivalent, sequence type 12 as well as five isolates of sequence type 657) for a total of 488 out of 748 (64.4%). This is similar to previous years with 61.3% in 2024, 68.0% in 2023, 71.1% in 2022 and 62.7% in 2021.Biotype 4 serotype O:3 (reported as sequence types 18 with 89 isolates and 276 with 1 isolate) was the next most common comprising 12% of all Y. enterocolitica. Other ystA containing reported strains were Biotype 2/3 serotype O:5 (reported as ST 14) and biotype 2/3 serotype O:3 (reported as ST429 and 206) with 15 and 3 isolates, respectively (2.0% and 0.4% of Y. enterocolitica). The remaining 152 isolates were all Biotype 1A (comprised of many sequence types and denoted by the presence of the ystB toxin gene) making up 20.3% of all Y. enterocolitica isolates. This is a decrease from a high in 2024 that had 206 Biotype 1As making up 29.4% of Y. enterocolitica for that year. Previous years were similar to the 2025 relative abundance with Biotype 1As making up 20.6% of Y. enterocolitica in 2023, 17.1% in 2022 and 17.3% in 2021. The most common sequence type of Biotype 1A was ST157 with 15 isolates (9.9% of Biotype 1As) while in 2024 it was ST278 with 12 isolates (17.6%). Y. pseudotuberculosis decreased to seven in 2025 from 12 in 2024 compared to five in 2023, nine in 2022 and 10 in 2021. It should be noted that Y. pseudotuberculosis is not included in standard enteric panels at all the diagnostic testing labs and may be underreported.