Invasive group A streptococcal disease surveillance in Canada, 2023

Background: Invasive group A streptococcal (iGAS, Streptococcus pyogenes) disease has been a nationally notifiable disease in Canada since 2000.Objective: To summarize the demographics, emm types and antimicrobial resistance of iGAS isolates collected in Canada in 2023. Methods:The Public Health Agency of Canada's National Microbiology Laboratory (Winnipeg, Manitoba) collaborates with provincial and territorial public health laboratories to conduct national surveillance of invasive Streptococcus pyogenes.Emm types were extracted from whole genome sequencing data and antimicrobial susceptibilities were predicted from the sequencing data based on the presence of resistance determinants.Results: Overall, the incidence of iGAS disease in Canada was 6.53 cases per 100,000 population in 2022; an increase from the rate of 5.56 cases per 100,000 population in 2021.A total of 5,201 iGAS isolates were collected during 2023, representing a stark increase in comparison to pre-SARS-CoV-2 pandemic disease activity.Of note during 2023 was the increased number of isolates collected from children younger than 15 years of age (n=577), over double the total in 2019 (pre-pandemic, n=254).The most common emm types overall in 2023 were emm1 (24.2%, n=1,260) and emm12 (16.6%, n=864), representing significant increases in prevalence since 2019 (p<0.0001);these types were also the most common within all Canadian regions and for both adults and children.Antimicrobial resistance rates in 2023 included 11.0% erythromycin resistance, 2.3% clindamycin resistance and 15.2% tetracycline resistance.Conclusion: The 5,201 isolates of iGAS collected in Canada in 2023 represent the highest annual total to date.The increase of iGAS experienced in 2023 was a critical public health concern, particularly due to the significant burden of pediatric invasive disease.Continued surveillance is vital to understanding the changing landscape of iGAS disease in Canada, particularly emm types and antimicrobial resistance patterns in the post-pandemic period.