Like the others have said - coughing, sneezing, touching a door handle, ride bars to pull down, lightswitches, etc. will all pass this virus around. In regards to doctors, no offense to any on here, but your doc's reaction doesn't surprise me. Docs very much read what patients want, and that is what they tell them - again, talk to the doctors in Orlando and they'll tell you of millions of stories of visitors who claim their docs said it was ok to travel, but the docs who deal with all of this crap in Orlando will tell you otherwise - people need to stay home!!! Mono is VERY easily passed - that's why he has it in the first place and the Strep, tonsil thing is right behind it - had my tonsils out by emergency surgery at 16.5 yrs. old as 4 years of being sick solid with my 'episodes' of Chronic Fatigue/Epstein Barr (they still to this day can't agree on what my issues are) and severe tonsillitis nearly killed me (severe Scarlet Fever as well - all related) and despite getting my tonsils removed, most days I feel like I've been driven over by a truck, still to this day - that's what Mono feels like. Your son is probably having trouble coping on a day to day basis, never mind going to Disney World.
For his safety, and the safety of all of the other thousands of people he could potentially infect, I urge you to rethink your vacation plans.
Tiger