Genomic characterizaton of invasive Group A Streptococcus (iGAS) isolates responsible for an outbreak in Bologna and Imola (Italy) between 2022 and 2024

Streptococcus pyogenes (Group A Streptococcus, GAS) is a well-known pathogen responsible for a wide range of diseases, including superficial infections (e.g., pharyngitis, impetigo) as well as severe invasive infections (iGAS) (e.g., necrotizing fasciitis, streptococcal toxic shock syndrome, and bacteremia). Clinical outcomes can vary widely, with invasive infections being associated with significant morbidity and mortality, particularly in vulnerable populations such as children, the elderly, and immunocompromised individuals. A remarkable increase in iGAS cases has been recently reported globally, likely due to post-pandemic shifts in population immunity and/or changes in healthcare access.This study focuses on the molecular characterization of 35 iGAS isolates collected in Bologna and Imola (Italy) from 2022 to 2024. By examining the distribution of antimicrobial resistance genes, virulence factors, emm types and emm clusters, the research aims to uncover potential associations between specific genomic features and the severity of clinical outcomes. Understanding these relationships is critical for elucidating the mechanisms underlying the invasiveness of GAS infections and guiding future strategies for prevention and management.Fifteen emm types were identified, with emm 1.0 and 1.3 being the most represented in our sample. Only emm75 was detected across multiple years. A total of 33 virulence genes were identified. Notably, phage-associated speA and speC were found in 48.6% and 42.8% of isolates, respectively. The presence of phage-associated virulence genes in specific emm types suggests their role in severe outcomes. Antimicrobial resistance genes were rare but included ermB and tetM.Continuous monitoring remains essential to detect emerging threats.