Group A streptococcal infections in Alberta, Canada 2018–2023

Group A streptococcal or <i>Streptococcus pyogenes</i> infections have been increasing post-COVID-19 pandemic. We describe the epidemiology of <i>S. pyogenes</i> pharyngitis and invasive disease in Alberta, Canada 2018-2023. Positive pharyngitis specimens were identified from throat swabs collected from pharyngitis patients. Invasive <i>S. pyogenes</i> was defined as the isolation of <i>S. pyogenes</i> from a normally sterile site or severe skin infection. <i>S. pyogenes</i> isolates were <i>emm</i> 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 <i>emm</i>1 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 <i>S. pyogenes</i> detected for an invasive disease rate of 0.06%. This descriptive epidemiology of <i>S. pyogenes</i> pharyngitis and invasive <i>S. pyogenes</i> disease highlights the rapid increase in cases of <i>S. pyogenes</i> occurring in western Canada and illustrates the critical need for a vaccine.