Knowledge center. Scarlet fever, also known as scarlatina, is a disease caused by a toxin (erythrogenic exotoxin) released by Streptococcus pyogenes or group A beta-hemolytic streptococcus-the disease occurs in a small percentage of patients with strep infections, such as strep throat or impetigo.auses of scarlet fever. Scarlet fever is caused by a bacterium called Streptococcus pyogenes, or group A beta-hemolytic streptococcus. This is the same bacterium that causes strep throat. When the bacteria release toxins scarlet fever symptoms occur, including the rash, Pastia's lines, red tongue and flushed face.