Group A strep (S. pyogenes) are the most common bacterial cause of acute pharyngitis (sore throat). About 20% of sore throat are caused by Group A Strep (the most of the rest cases by viruses).SYMPTOMS (2-4 days) PHARYNGITIS generally develops 2 to 4 days after exposure to the pathogen.It starts with an abrupt onset of soar throat, fever, malaise and headache.roup A strep (S. pyogenes) are the most common bacterial cause of acute pharyngitis (sore throat). About 20% of sore throat are caused by Group A Strep (the most of the rest cases by viruses).