Group A streptococcal infections in Alberta, Canada 2018-2023.

Group A streptococcal or Streptococcus pyogenes infections have been increasing post-COVID-19 pandemic. We describe the epidemiology of S. pyogenes pharyngitis and invasive disease in Alberta, Canada 2018-2023. Positive pharyngitis specimens were identified from throat swabs collected from pharyngitis patients. Invasive S. pyogenes was defined as the isolation of S. pyogenes from a normally sterile site or severe skin infection. S. pyogenes isolates were emm typed. Pharyngitis and invasive disease displayed seasonal trends preceding the COVID-19 pandemic followed by a sharp decrease during COVID-19 intervention measures. After the lifting of interventions, rates of pharyngitis and invasive disease rose. There were 182 983 positive pharyngitis specimens between 2018 and 2023 for a positivity rate of 17.6%. The highest rates occurred in the 0-9 age group in 2023 (41.5%). Invasive disease increased in 2022-2023 driven by emm1 and 12 types. M1_UK strain was the most frequent M1 type associated with invasive disease (59% of M1 isolates sequenced). Notably, out of 182 983 pharyngitis cases, there were 111 cases of invasive S. pyogenes detected for an invasive disease rate of 0.06%. This descriptive epidemiology of S. pyogenes pharyngitis and invasive S. pyogenes disease highlights the rapid increase in cases of S. pyogenes occurring in western Canada and illustrates the critical need for a vaccine.