Streptococcal sore throat, or strep throat, is an inflammation of the throat and tonsils caused by bacteria of the group A hemolytic Streptococcus, hence its name. It is the most common type of strep infection; others include scarlet fever. Onset is usually sudden and is accompanied by pain, redness, and swelling in throat tissues, pus on the tonsils, fever, headache, and malaise. Abdominal pain and nausea may occur, especially in children. If left untreated, strep throat can led to rheumatic fever. The peak incidence of strep throat occurs in winter. Penicillin is the usual treatment, unless the patient is allergic. Viral infections can mimic strep throat.