Germs are on food sometimes. Usually your gut will kill them, but maybe not always. They can't get through the walls of your digestive tract, so they go on through and come out in your poop. if you touch your poop, you pick up those germs and they get another chance at making you sick. So you try not to touch the poop, and you wash your hands before you leave the bathroom.
Do you fold the tp? Bacteria in poop can go through up to ten layers of tp in some brands. So wash your hands even if you think they are clean.
