I'm like GLC, in that I don't routinely think about germs. I used to get sick all of the time, but since I started spending more time outdoors, it's decreased immensely. So while I have some chronic things, I just don't worry about stuff like this.
I rode through a lot of farm country on my recent Vermont tour, but with no ill effects. When I told DH about the chicken poop issue based on this thread, he said it traumatized him and couldn't get it out of his head!