Spread of Virulent Group A Streptococcus Type emm59 from

Full-genome sequencing showed that a recently emerged and hypervirulent clone of group A Streptococ-cus type emm59 active in Canada and parts of the United States has now caused severe invasive infections in ru-ral northeastern Wyoming. Phylogenetic analysis of ge-nome data indicated that the strain was likely introduced from Montana. Strains of group A Streptococcus (GAS) type emm59 historically have not been commonly associated with invasive infections. However, a striking increase in the fre-quency and severity of invasive infections caused by type emm59 strains recently occurred in Canada (1). Four of the authors (M.L.M., P.L.F., R.N., and M.M.) cared for 4 patients whose cases were temporally clus-tered and who had severe invasive infections caused by GAS in northeastern Wyoming, USA. Of the 4 case-patients, 2 were directly linked. Case-patient 4 contracted invasive infection from a close-contact family member (case-patient 2). Case-patient 3 was a physician who had cared for case-patients 1 and 2. These infections occurred in an area close to where a cluster of 6 invasive emm59 infections occurred in Montana in 2010 (2). This fact led us to determine whether genetically related emm59 strains were responsible. Full-genome sequencing confirmed this hypothesis (Figure)