Group A streptococcus refers to Streptococcus pyogenes, which is b-hemolytic and has a clear ring of 2-4 mm around the cultured colonies, called b-hemolytic.The more famous diseases that can be caused by group A streptococcus are scarlet fever, which is an infectious disease. Group A streptococci can also cause pharyngitis, tonsillitis, lymphangitis of the lower extremities (commonly known as dermatitis) and other skin and soft tissue infections, and are the most common type of streptococcus causing human disease.