Background Since 2022, many countries reported an upsurge in invasive group A streptococcal (iGAS) infections. We explored whether changes in S. pyogenes carriage rates or emergence of more virulent strains, such as emm 1 variants M1 UK and M1 DK , contributed to the 2022/2023 surge in the Netherlands. Methods We determined emm (sub)type distribution for 2,698 invasive and 351 S. pyogenes carriage isolates collected between January 2009 - March 2023. Genetic evolution of emm 1 was analyzed by whole-genome sequencing of 497 emm 1 isolates. Findings The nationwide iGAS upsurge coincided with a sharp increase of emm 1.0 from 18% (18/100) of invasive isolates in Q1 2022 to 58% (388/670) in Q1 2023 (Fisher’s exact, p<0.0001). M1 UK became dominant among invasive emm 1 isolates in 2016 and further expanded from 72% in Q1 2022 to 96% in Q1 2023. Phylogenetic comparison revealed evolution and clonal expansion of four new M1 UK clades in 2022/2023. DNase Spd1 and superantigen SpeC were acquired in 9% (46/497) of emm 1 isolates. S. pyogenes carriage rates and emm 1 proportions in carriage isolates remained stable during this surge and the expansion of M1 UK in iGAS was not reflected in carriage isolates. Interpretation During the 2022/2023 iGAS surge in the Netherlands, expansion of four new M1 UK clades was observed among invasive isolates but not carriage isolates, suggesting increased virulence and fitness of M1 UK compared to contemporary M1 strains. The emergence of more virulent clades has important implications for public health strategies such as antibiotic prophylaxis for close contacts of iGAS patients.
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Rümke et al. (2024) studied this question.
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