But who says that people actually spit on the cake ? I just made a comment about not being allowed to have birthday cakes because someone may sneeze, spit, cough etc near the cake. It's all about care and hygiene and may I say parents taking responsibility.

Well, it would be those people who have seen young children do it, obviously.  We are talking about childcare centres and as I said before, unfortunately, not all parents do the responsible thing by keeping sick kids at home.  There is a very good reason why children are taught from a very young age not to share water bottles or drinking cups.   It is for that reason that blowing out candles by kids in childcare should not be recommended.  IMO