My son had his tonsils out at age 4 - now at age 20 he is getting tonsillitis again ( 3rd time now in 3 months). does he need tonsillectomy again?

It's possible: If they didn't get all of the tonsillar tissue the first time or if it just grew back. They sometimes have to repeat the procedure but it is rare and he doesn't quite meet the criteria yet. Wait and see if he continues to get them. Also, could try gargling w/peroxide to keep bacteria levels down and see if that helps. A bit unconventional but I have had some success w/reducing recurrent strep

Hard to say: You do not end the possibility of throat infections with a tonsillectomy,ever. Some will always label a throat infection tonsillitis even though they play a minor role in the infection. The tissues of the mouth and throat are weak compared to skin and the most common portal for invasion by germs. Good hand washing and avoiding exposure are the best way to reduce infections.