How many doorknobs do you typically touch outside of your home a day? Most doors here are automatic. Plus, I would be reluctant to use someone else's keyboard at work, even.
But...why? Do you have an autoimmune disorder? Generally find yourself especially vulnerable to the errant bug? How do you feel when you breath in someone's fart? You're a walking bag of mud expressing discomfort at other bits of mud in the world. One bit in a million might be annoying. One in a billion actually painful.