Scarlet fever is an infectious disease which most commonly affects 4–8-year-old children. Symptoms include sore throat, fever and a characteristic red rash. Scarlet fever is usually spread by inhalation. There is no vaccine, but the disease is effectively treated with antibiotics. Most of the clinical features are caused by erythrogenic toxin, a substance produced by the bacterium Streptococcus pyogenes (group A strep.) when it is infected by a certain bacteriophage. Before the availability of antibiotics, scarlet fever was a major cause of death. It also sometimes caused late complications, such as glomerulonephritis and endocarditis leading to heart valve disease, all of which were protracted and often fatal afflictions at the time.