sore throat, streptococcal (strĕpˌtəkŏkˈəl) [key], infection and inflammation of the pharynx caused by certain streptococcal bacteria. These organisms are known as hemolytic streptococci because they secrete toxins that dissolve, or cause hemolysis of, red blood cells. Acute streptococcal sore throat is usually characterized by an extremely painful throat, enlarged tonsils, and sometimes gastrointestinal disturbances. Scarlet fever, which is caused by the same streptococcal bacteria, occurs when the microorganisms produce a toxin that, in sensitive individuals, causes appearance of a characteristic rash. Complications of streptococcal infection, which include rheumatic fever and sometimes arthritis and nephritis, can be prevented by early, vigorous treatment with penicillin or other suitable antibiotics.