Strep throat is caused by the Streptococcus bacteria. It is the most common childhood bacterial infection of the throat. Strep 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 from nasal secretions or saliva, often among family or household members. Children with Strep throat get sick 2–5 days after they are exposed. The illness may begin suddenly, with a fever that peaks on the second day. Many kids also have a sore throat, headache, stomachache, nausea, or chills. In some children, Strep throat is very mild, with only a few symptoms. In others, Strep throat may be severe.
There are many strains of Strep. There are some strains that produce toxins that can lead to a scarlet fever rash. This rash is thought to be an allergic reaction to the toxins. Untreated, Strep throat can sometimes lead to rheumatic fever or kidney complications.