What causes sore throat?

Sore throat, or pharyngitis, is an infection of the throat (and sometimes the tonsils). It is most commonly caused by bacteria called Streptococcus, which then becomes known as "strep throat." Strep throat can cause severe complications such as rheumatic fever (a disease of the heart valves), so it is important to get treatment for your child right away if he or she has strep throat.

What are the signs and symptoms of strep throat?