Sore throats are usually caused by viruses, although an infection in the throat and tonsils called Group A Streptococcus (group A strep) is caused by bacteria.This infection lives in the nose and throat, easily spread to others by coughing and sneezing, creating small respiratory droplets containing bacteria. Although coughing and sneezing are the common methods of spreading the bacteria causing strep throat, there are many more ways to look out for to prevent you and your child from contracting this infection.