Strep throat is caused by the bacteria Streptococcus pyogenes. (Most sore throats are caused by a virus & are associated with colds & flu.) Common symptoms of strep throat are sudden sore throat, high fever, fatigue, & swollen tonsils/lymph nodes. Symptoms of colds/flu that are usually not present in strep throat are cough & runny nose. Rapid diagnosis is important for 2 reasons -- First, unlike colds/flu, strep throat is readily treatable with antibiotics & second, several serious complications can occur after prolonged, untreated strep infection. (Picture from CDC; Text paraphrased from several sources below.)