When someone is backpacking for several days, washing hands with soap might not always be possible, or inconvenient (e.g. because of soap polluting the water; you want to minimize the weight of your pack, ...). However, some resources, such as the Backpacker's Field Manual strongly recommend either using soap, or some hand sanitizer, and claim that gastroenteritis is likely to occur if they are not used. The main argument here is that even healthy individuals can contract gastroenteritis from contact of their own feces, if they don't wash their hands thoroughly enough.
While I agree that washing hands is reasonable, I wonder if soap or sanitizers are really necessary in most cases? This is mainly due to 2 questions:
Apparently, washing hands simply with water already decreases the amount of bacteria on your hands significantly. Shouldn't this be enough when on a hike? (Unless you were in contact with someone who has Salmonella, ..., i.e. some serious illness).
Do bacteria (like E.coli, in particular) die after a while when on the skin anyway?
Is it true that when outdoors for several days and no means of using soap or a hand sanitizer, but washing hands simply with water, one is at a notably higher risk of contracting some kind of gastroenteritis?