Clinical and population genomic epidemiology of invasive group A streptococcus in Scotland, 2014-2024

Following the COVID-19 pandemic, multiple countries reported a surge in invasive group A streptococcus (iGAS) infections. Posited explanations include reduced population immunity, increased respiratory virus co-infection, and emergence of hypervirulent GAS clones. To assess the relative contribution of these factors, we analyzed the epidemiology and genomics of 3,408 iGAS infections in Scotland.

National surveillance data from 2014-2024 were analyzed to characterize iGAS incidence. Hybrid whole genome sequencing was used to comprehensively genetically characterize 404 emm1 isolates collected from invasive and tonsillitis infections.

iGAS incidence markedly increased in late 2022 and early 2023, disproportionately affecting children and older adults. This surge was not associated with a proportional increase in bacteremia but did coincide with increased influenza and respiratory syncytial virus infections. Genomic analyses found that emm1 post-pandemic isolates were not genetically distinct from pre-pandemic isolates in genome-wide polymorphisms, accessory genes including virulence and antimicrobial resistance determinants, mobile genetic elements, or chromosomal structural variants.

The post-pandemic iGAS surge in Scotland was not associated with emergence of a novel hypervirulent emm1 clone. Instead, the epidemiologic and population genomic findings are consistent with increased host susceptibility following reduced pathogen exposure during the pandemic and increased respiratory virus co-infection as predominant contributing factors.