Two reasons to wash your hands for at least fifteen seconds with soap after using the restroom and throughout the day:
1) So you don't spread disease to others
2) Because not everyone else is doing it...
...for example, the guy who came out of one of the stalls earlier today, rinsed his hands for a second in water, and then left. Trust me that any bug that can make you sick is fine with being moistened for a second or two.