The name 'strep' throat comes from the type of bacteria that is known to cause the infection, Group A Streptococcus (GAS). The infection is identified by the presence of certain specific symptoms. These symptoms vary depending upon the causative agent. A bacterial infection produces signs of throat redness and swollen uvula in the mouth, whereas a viral infection leads to swollen tonsils. The symptoms may include irritation, redness, and the build-up of pus in the back of the throat in some cases.