Invasive group A streptococcal disease surveillance in Canada, 2020

Abstract

Background: Invasive group A streptococcal (iGAS) disease (caused by Streptococcus pyogenes) has been a nationally notifiable disease in Canada since 2000. This report summarizes the demographics, emm types and antimicrobial resistance of iGAS infections in Canada in 2020.

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 S. pyogenes. Emm typing was performed on all isolates using the Centers for Disease Control and Prevention emm sequencing protocol. Antimicrobial susceptibilities were determined using Kirby-Bauer disk diffusion according to Clinical and Laboratory Standards Institute guidelines. Population-based iGAS disease incidence rates up to 2019 were obtained through the Canadian Notifiable Disease Surveillance System.

Results: Overall, the incidence of iGAS disease in Canada has increased from 4.0 to 8.1 cases per 100,000 population from 2009 to 2019. The 2019 incidence represents a slight decrease from the 2018 rate of 8.6 cases per 100,000 population. A total of 2,867 invasive S. pyogenes isolates that were collected during 2020 are included in this report, representing a decrease from 2019 (n=3,194). The most common emm types in 2020 were emm49 (16.8%, n=483) and emm76 (15.0%, n=429), both increasing significantly in prevalence since 2016 (p<0.001). The former most prevalent type, emm1, decreased to 7.6% (n=217) in 2020 from 15.4% (n=325) in 2016. Antimicrobial resistance rates in 2020 included 11.5% resistance to erythromycin, 3.2% resistance to clindamycin and 1.6% nonsusceptibility to chloramphenicol.

Conclusion: Though the number of collected invasive S. pyogenes isolates decreased slightly in 2020 in comparison to previous years, iGAS disease remains an important public health concern. The emm distribution in Canada has been subtly shifting over the past five years, away from common and well-known emm1 and towards emm49 and emm76. It is important to continue surveillance of S. pyogenes in Canada to monitor expanding replacement emm types, as well as outbreak clones and antimicrobial resistance.

Keywords: Canada; Streptococcus pyogenes; antimicrobial resistance; emm; group A streptococcus; iGAS; surveillance.

Figure 1

Annual incidence rates of invasive Streptococcus pyogenes cases in Canada by age group, 2010–2019 ^a Cases per 100,000 population

Figure 2

Prevalence of invasive Streptococcus pyogenes emm types in Canada, 2016–2020^{a,b,c a} Number of isolates for 2016, 2017, 2018, 2019 and 2020, respectively ^b Increase in 2016 and 2017 totals from previous annual reports is due to inclusion of submitted data from Alberta ^c For emm types with an overall (2016–2020) n≥30: up or down arrows indicate statistically significant trends toward increasing or decreasing prevalence for the 2016–2020 timespan, using the chi-squared test for trend. Emm types with no arrow either did not demonstrate a statistically significant trend, or did not have an overall n≥30

Figure 3

Regional distribution of invasive Streptococcus pyogenes isolates collected in 2020, by emm type^{a a} Number of isolates in the Northern, Eastern, Central and Western regions of Canada, respectively

Figure 4

Antimicrobial resistance of invasive Streptococcus pyogenes in Canada, 2016–2020 Abbreviation: CHL-NS, chloramphenicol-nonsusceptible (resistant or intermediate); CLI-R, constitutively clindamycin-resistant; ERY-R, erythromycin-resistant