Streptococcus Isolates Recovered From Pharyngitis in the United States emm Type emm Cluster No.

TO THE EDITOR—A new emm-cluster typ-ing system has been recently proposed for group A Streptococcus (GAS) [1].This sys-tem classifies most of the 223 emm types [2] into 48 functional emm clusters con-taining closely related M proteins that share structural properties. emm clusters help to predict the virulence potential of any GAS isolate by ascribing M protein binding attributes to emm types belonging to the same emm cluster [1, 3]. This system correlates with M protein vaccine antigen content and serves as a frame-work to investigate immunologic cross-protection between emm types [1, 4, 5]. emm clusters have been used to analyze the epidemiology of GAS in the Pacific region, which is characterized by high GAS disease burden and a great variety of circulating emm types [6, 7]. The emm-cluster system identified epide-miologic similarities across the Pacific region and highlighted vaccine target priorities [8]. We applied the emm-cluster system to GAS epidemiology in a high-income set-ting by analyzing prospective surveillance data for GAS pharyngitis in North Amer-ica, 2000–2007 [9]. A total of 56 and 33 different emm types were recovere