DefinitionStrep throat is caused by Group A Streptococcusbacteria. It is the most common bacterial infection of the throat.Alternative NamesPharyngitis - streptococcal; Streptococcal pharyngitisCauses, incidence, and risk factorsStrep throat is most common in children between the ages of 5 and 15, although it can happen in younger children and adults. Children younger than 3 can get strep infections, but these usually don't affect the throat.Strep throat is most common in the late fall, winter, and early spring. The infection is spread by person-to-person contact with nasal secretions or saliva, often among family or household members.There are many strains of strep. Some strains can lead to a scarlet fever rash. This rash is thought to be an allergic reaction to toxins made by the strep g