Dynamics of emm types in invasive Streptococcus pyogenes isolates from Argentina, 2018-2024.

Group A Streptococcus (GAS) is a major cause of invasive bacterial infections worldwide, making molecular surveillance essential for monitoring strain dynamics and detecting emerging lineages. We conducted nationwide molecular surveillance of invasive GAS (iGAS) infections in Argentina between July 2018 and December 2024, analyzing 1127 isolates from confirmed cases. emm typing was performed using Sanger sequencing (2018-2020) and whole-genome sequencing (WGS) (2022-2024), enabling multilocus sequence typing (MLST), virulence and antimicrobial resistance profiling. Surveillance was interrupted during 2020-2021 due to the COVID-19 pandemic but was strengthened thereafter when iGAS became nationally notifiable. Overall, 59 emm types and 61 sequence types were identified. emm1 predominated across the study period (42.4%), followed by emm12, emm3, and emm4, with marked temporal shifts. In 2023, clonal diversity declined, with emm1 and emm12 accounting for 72% of isolates and the emergence of hypervirulent M1 lineages. In 2024, emm diversity increased, with expansion of emm3, emm4, emm49, and emm87.