Expansion of Invasive Group A Streptococcus M1UK Lineage in Active Bacterial Core Surveillance, United States, 2019‒2021

From 2015–2018 to 2019‒2021, hypertoxigenic M1 UK lineage among invasive group A Streptococcus increased in the United States (1.7%, 21/1,230 to 11%, 65/603; p<0.001). M1 UK was observed in 9 of 10 states, concentrated in Georgia (n = 41), Tennessee (n = 13), and New York (n = 13). Genomic cluster analysis indicated recent expansions.