Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Update on invasive group A streptococcus hypervirulent M1UK clone in Canada 2024 (#11)

Gregory J Tyrrell 1 , Alyssa R Golden 2 , Averil Griffith 2 , Julianne V Kus 3 , Allison McGeer 4 , Marc-Christian Domingo 5 , Jennifer M Grant 6 , Jessica Minion 7 , Paul Van Caeseele 8 , Guillaume Desnoyers 9 , Elizabeth Simms 10 , Robert Taylor 11 , Xiaofeng Ding 12 , Laura Steven 13 , Jan McFadzen 14 , Courtney Primeau 15 , Irene Martin 2
  1. Provincial Laboratory for Public Health (Microbiology), Edmonton
  2. Public Health Agency of Canada - National Microbiology Laboratory, Winnipeg, MANITOBA, Canada
  3. Public Health Ontario, Toronto
  4. Toronto Invasive Bacterial Diseases Network, Mount Sinai Hospital, Toronto
  5. Laboratoire de santé publique du Québec, Ste-Anne-de-Bellevue
  6. British Columbia Centre for Disease Control, Vancouver
  7. Roy Romanow Provincial Laboratory, Regina
  8. Cadham Provincial Laboratory, Winnipeg
  9. Laboratoire de santé publique du New Brunswick, Moncton
  10. Queen Elizabeth II Health Science Centre, Halifax
  11. Newfoundland Public Health Microbiology Laboratory, St. John's
  12. Queen Elizabeth Hospital, Charlottetown
  13. Stanton Territorial Hospital Laboratory, Yellowknife
  14. Yukon Communicable Disease Control, Government of Yukon, Whitehorse
  15. Centre for Emerging and Respiratory Infections and Pandemic Preparedness, Public Health Agency of Canada, Ottawa

Background: The hypervirulent M1UK lineage of group A Streptococcus (GAS) has been associated with increased notifications of scarlet fever and invasive GAS (iGAS) infections. Following a sharp increase in the incidence of iGAS infections worldwide following the COVID-19 pandemic, we previously reported on the distribution of M1UK in Canada up to 2023. Here we provide an update on the prevalence of emm1/M1UK in Canada through 2024.

Methods: To date, we have performed whole genome sequencing (WGS) on (or received genomic data for) 4,579 iGAS isolates collected in 2024, including 1,215 emm1. M1UK isolates were identified by mapping WGS reads to reference strain MGAS5005 and identifying 27 characteristic single nucleotide variants. Statistical significance was assessed using the Cochran-Armitage trend test.

Results: Overall the prevalence of emm1 in 2024 has been high at 26.5%, a similar rate to 2023 (24.2%) and significant increase since 2020 (8.2%, P<0.0001). However, during 2024 the prevalence of emm1 decreased each quarter, starting at a high of 38.1% in January-March, 27.8% in April-June, 15.6% in July-September and hitting a low of 8.5% in October-December. Amongst emm1 isolates, the M1UK lineage has increased in prevalence since 2020, from 48.9% to 68.6% in 2024 (P<0.0001). Despite the gradual decrease in emm1 prevalence in 2024, the proportion of M1UK has remained consistent, ranging from 67-73% of emm1 each quarter.

Conclusions: Despite gradually decreasing throughout the year, emm1 prevalence remained high in Canada in 2024. M1UK was the most common emm1 lineage and continues to replace the M1global lineage in Canada.