How long does it take until symptoms of strep throat go away with treatment?

1-3 days. Strep is a bacteria that remains very sensitive to penicillin. If treated by mouth it can take 2-3 days to become non contagious. If treated with cr bicillin injection the contagious period is shorter and sometimes more effective. My choice is the shot, your child will feel better quickly and can return to school as early as 24 hours after the shot.