The problem with getting a dr.'s note is that you may get a different opinion from different doctors. I had asked the doctor if bronchitis is contagious; he said it isn't. After that I had been to the walk-in clinic and asked another dr. the same question and she had said that bronchitis IS contagious.
I have pretty responsible parents and find that in the last couple of years there's been less sickness going through my daycare. My current parents seem to keep their kids home when their kids are sick. I imagine that when I start getting different parents that will change again.