The pathophysiological mechanisms of invasive GAS infections are poorly understood. These mechanisms could involve not only virulence factors of the bacterium ( M protein determines the emm genotype , but also super- antigenic exotoxins SpeA , Spe C, Ssa, Sme z or other virulence genes , SilC , ... Sic ), but also in some cases, factors associated with host immunity in particular in the absence of risk factors for invasive skin infection such as cutaneous effraction ( wound , burn , chicken pox ) , corticosteroids or other immunosuppressive therapy and recent surgery .