I almost always wait for someone to open the door if there's no way to do so without touching nasty door handles. Or find a tiny piece of paper to use and discard afterward. Or hold the door with my feet while I clean my hand after opening the door with it, if possible. When I go to restaurants sometimes I carry a paper napkin if I have been to the place and know it's complicated to get out without touching anything. Yeah, I'm that paranoid with it...

* Heck, I even change clothes when I get home before seating in my bed or sofa.