It's fecal matter that really does it to me. Food left to sit long term is pretty much a petri dish. You don't need a lot of people to spread it. Just one person who's combing unwillingness to wash their hands with lazy utensil usage can spread enough shit to start bacteria growing all over it. And the worst part is that the grossest people are also the ones most commonly getting their hands over everything.  You have to look around and ask yourself if you'd lick the hands of the grossest person there. Because you essentially are.