Evidence for early circulation of the M1UK sublineage of Streptococcus pyogenes in Germany, 2015–2023

Several European countries have reported a rise in invasive Group A <i>Streptococcus</i> (GAS) infections, particularly linked to the toxigenic <i>emm1</i> sublineage M1_UK. In Germany, historical molecular data are limited due to the absence of systematic molecular surveillance. We performed whole-genome sequencing (WGS) on 189 invasive <i>Streptococcus pyogenes</i> isolates collected between January 1, 2015, and May 31, 2023, at University Medical Center Carl Gustav Carus, TU Dresden. Clinical data were extracted from patient records. M1_UK sublineage identification was based on 27 characteristic single nucleotide polymorphisms (SNPs). A Bayesian coalescent analysis estimated the evolutionary timescales of the M1_UK clade in Germany. The most common <i>emm</i> type was <i>emm1</i> (34%, 64/189), followed by <i>emm12</i>, <i>emm4</i>, and <i>emm89</i>. Of the 64 <i>emm1</i> isolates, 31 (48%) were M1_UK. No significant associations were found between clinical outcomes and M1_UK or M1_global genotypes. Although a post-pandemic shift favouring M1_UK was observed, our analysis indicates that M1_UK had already been circulating in Germany by 2017. The estimated most recent common ancestor dates to 2012 (95% highest posterior density: 2009–2015), with a stable effective population size over time. Our findings confirm the pre-pandemic circulation of M1_UK in Germany. While the clinical impact of M1_UK remains unclear, integrating clinical data with high-resolution molecular surveillance may improve early detection of emerging high-risk clones.