Added Value of the emm-Cluster Typing System to Analyze Group A Streptococcus Epidemiology in High-Income Settings

TO THE EDITOR—A new emm-cluster typing system has been recently proposed for group A Streptococcus (GAS) [1].This system classifies most of the 223 emm types [2] into 48 functional emm clusters containing 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 framework to investigate immunologic crossprotection 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 epidemiologic similarities across the Pacific region and highlighted vaccine target priorities [8]. We applied the emm-cluster system to GAS epidemiology in a high-income setting by analyzing prospective surveillance data for GAS pharyngitis in North America, 2000–2007 [9]. A total of 56 and 33 different emm types were recovered from 7040 US and 1434 Canadian GAS