Group A streptococcal infections in Alberta, Canada 2018-2023

Area of Science:

• Infectious Diseases
• Epidemiology
• Microbiology

Background:

• Group A Streptococcus (GAS) infections, including Streptococcus pyogenes, have shown increasing incidence globally post-COVID-19.
• Understanding the epidemiological trends of S. pyogenes pharyngitis and invasive disease is crucial for public health interventions.

Purpose of the Study:

• To describe the epidemiology of S. pyogenes pharyngitis and invasive disease in Alberta, Canada, from 2018 to 2023.
• To identify trends in incidence, seasonality, and prevalent emm types associated with S. pyogenes infections.

Main Methods:

• Retrospective analysis of S. pyogenes isolates from pharyngitis cases (throat swabs) and invasive disease (sterile sites or severe skin infections).
• emm typing of S. pyogenes isolates to characterize circulating strains.
• Analysis of epidemiological data including seasonality, age distribution, and incidence rates.

Main Results:

• A total of 182,983 positive pharyngitis specimens were recorded (17.6% positivity rate) between 2018-2023.
• Pharyngitis and invasive disease rates decreased during COVID-19 interventions, then rose sharply afterward, with the highest pharyngitis rates in children aged 0-9 in 2023 (41.5%).
• Invasive disease increased in 2022-2023, driven by emm1 and emm12 types, with the M1_UK strain being most frequent (59% of M1 isolates).

Conclusions:

• S. pyogenes infections, both pharyngitis and invasive disease, have significantly increased in western Canada following the COVID-19 pandemic.
• The rise in invasive disease is linked to specific emm types, emphasizing the need for targeted surveillance.
• The findings underscore the critical need for the development and implementation of an S. pyogenes vaccine.