I have to admit.. I've never worried one iota about bathroom doors. Don't know if that's a good thing or a bad thing, but it's a thing.
You can't be paranoid about everything. It's just not healthy.
The current "hand sanitizer" phase is actually going to make bugs harder to kill. Over use of hand sanitizers just kills the weaker versions of a bug and gives the truly nasty one more room to grow (kinda like alcohol only killing the slow, weak brain cells ). We are making ourselves sicker in the long run by avoiding every "bad" thing we might run into. I've seen studies that show kids who eat dirt (i.e. play outside, get dirty, have fun, you know like we did as kids) are smarter and healthier than kids raised in cleaner environments.
I wash my hands and throw the towel away in the trash can. I will also will say that there are some bathrooms around that make that very hard to do but since you're already in them, any damage is already done.