Sore throat refers to the inflammation of the pharynx or back of the throat. It occurs frequently when a person has a cold or an attack of influenza. 10% of sore throat may be due to strep throat infection. Strep throat is an infection of the pharynx, caused by group A streptococcus bacteria, whereas sore throat may be a viral or a bacterial infection. Strep throat is common among children and teenagers, between the ages of 5 to 15.