Emergent Invasive Group AStreptococcus dysgalactiaesubsp.equisimilis, United States, 2015–2018

The term group A Streptococcus is considered synonymous for the species Streptococcus pyogenes. We describe an emergent invasive S. dysgalactiae subspecies equisimilis lineage that obtained the group A antigen through a single ancestral recombination event between a group C S. dysgalactiae subsp. equisimilis strain and a group A S. pyogenes strain.