Invasive Group A Streptococcal Disease Surveillance in Canada, 2021-2022

Background: Invasive group A streptococcal (iGAS, ) disease has been a nationally notifiable disease in Canada since 2000. This report summarizes the demographics, types, and antimicrobial resistance of iGAS isolates collected in Canada in 2021 and 2022.

Methods: The Public Health Agency of Canada's National Microbiology Laboratory collaborates with provincial and territorial public health laboratories to conduct national surveillance of invasive . typing was performed using the Centers for Disease Control and Prevention sequencing protocol or extracted from whole-genome sequencing data. Antimicrobial susceptibilities were determined using Kirby-Bauer disk diffusion according to Clinical and Laboratory Standards Institute guidelines or predicted from whole-genome sequencing data based on the presence of resistance determinants.

Results: Overall, the incidence of iGAS disease in Canada was 5.56 cases per 100,000 population in 2021, decreasing from the peak of 8.6 cases per 100,000 population in 2018. A total of 2,630 iGAS isolates were collected during 2022, representing an increase from 2021 (n=2,179). In particular, there was a large increase in isolates collected from October to December 2022. The most predominant type overall in 2021 and 2022 was 49, at 21.5% (n=468) and 16.9% (n=444), respectively, representing a significant increase in prevalence since 2018 (<0.0001). The former most prevalent type, 1, increased from 0.5% (n=10) in 2021 to 4.8% (n=125) in 2022; similarly, 12 increased from 1.0% (n=22) in 2021 to 5.8% (n=151) in 2022. These two types together accounted for almost 25% of isolates collected in late 2022 (October to December). Antimicrobial resistance rates in 2021 and 2022 included: 14.9%/14.1% erythromycin resistance, 4.8%/3.0% clindamycin resistance, and <1% chloramphenicol resistance.

Conclusion: The increase of iGAS isolates collected in Canada is an important public health concern. Continued surveillance of iGAS is critical to monitor expanding types and antimicrobial resistance patterns.