Streptococcus pyogenes (group A strep) is responsible for scarlet fever. It can also cause simple angina, erysipelas and serious toxin-mediated syndromes like necrotizing fasciitis and the so-called streptococal toxic shock-like syndrome. The virulence of group A strep seems to be increasing lately. The exanthem of scarlatina is thought to be due to erythrogenic toxin production by specific streptococcal strains in a nonimmune patient. Along with erythrogenic toxins, the Group A strep produces several toxins and enzymes. Two of the most important are the streptolysins O and S. Streptolysin O, an hemolytic, thermolabile and immunogenic toxin, is the base of an assay for scarlatina and erysipelas – the anti-streptolysin O titer.