strep throat is included in the broader category of sore throat or pharyngitis. about 11 million people get sore throats in the united states each year. most cases of sore throat are caused by viruses. the bacteria group a beta-hemolytic streptococcus causes 15 to 30 percent of sore throats in children. it causes 5 to 20 percent of sore throats in adults. cases usually happen in late winter and early spring.