Most cases of erysipelas are due to Streptococcus pyogenes (also known as beta-hemolytic group A streptococci), although non-group A streptococci can also be the causative agent. The rash is due to an exotoxin, not the Strep. bacteria itself and is found in areas where no bacteria are present - e.g. the infection may be in the nasopharynx, but the rash is found usually on the face and arms or legs.
