Strep throat is caused by the bacterium known as Streptococcus pyogenes, also referred to as group A streptococcus or group A strep (GAS). Group A streptococcus is spread through direct contact with respiratory discharges from the nose or throat of an individual who has an active strep throat infection. Such discharges can occur when the infected individual coughs, sneezes, or shares food or beverages with another person. You can also become infected with strep throat after touching a surface contaminated with group A strep bacteria and then touching your nose or mouth.