Strep throat is a bacterial infection of the throat and tonsils caused by group a streptococcus. Learn the causes of streptococcal pharyngitis and how to tell strep from other sore throat conditions. strep throat is a bacterial infection that causes inflammation and pain in the throat. We explain the common signs, diagnostic tests, treatment options, and potential complications. Strep throat is a bacterial infection that can make your throat feel sore and scratchy. Strep throat accounts for only a small portion of sore throats. If untreated, strep throat can cause complications, such as kidney inflammation or rheumatic fever. Your doctor tests for strep throat with a rapid antigen test. She swabs the back of your throat with a cotton-tipped stick to get a sample. Strep throat mouth ulcers or canker sores are not usually a symptom of strep throat. However, having an infection such as strep throat can compromise your immune. Streptococcal pharyngitis, also known as strep throat, is an infection of the back of the throat including the tonsils caused by group a streptococcus (gas). Common symptoms include fever, sore throat, red tonsils, and enlarged lymph nodes in the neck. Some develop a sandpaper-like rash which is known as scarlet fever. Symptoms typically begin one to three days after exposure and last seven to ten days.