My daughter had recurrent strep throats for 5- 6 years. Sometimes when she was a baby the throat cultures did not come back positive, but the doctors could see the tell-tale patches on her throat. She had scarlet fever. She could not be near anyone getting over a slight cold without getting sick ( often with strep). The doctors thought I was exagerating until they did a throat culture on her (healthy) and it came back with Beta 4 strep. They tested her ability to fight disease etc. Finally, she would be negative while on antibiotics and positive 12-24 hours when she went off them. They removed her tonsils and adenoids and found that she had tunnels through them( they said that they looked like swiss cheese) and the antibiotics wern't really getting to them. She had them out at age 6 and is now 34. She hasn't had any strep. since, but did fight impetigo or herpes for the longest time. The tonsils were filtering that, but not strep. That is an occasional problem now, but is very manageable.