I'm a biology student so I can get paranoid about small details regarding germs.
Sometimes you just have to let things go.
Until a century and a half ago, the human race had no idea that germs existed at all. "Surgeons" performed their operations such as amputations and blood-letting without washing their hands or their instruments. There was a communal cup at the well that everyone drank from. Bathing was a weekly/monthly/annual event. Refrigeration was unheard-of. Yes, people died young and mortality rates were high (what the heck does that mean, anyway? the "mortality rate" has always been 100% and always will be).
Not to say that you should not be clean and careful, but how many billions of germs are swarming on your skin right now, and how many do you suck in with every breath you take?
And not to mention "social" activities such as shopping, public transportation, meetings, any team or spectator sport, having sex, or any manual labor .....
There is no "iron-clad" immune system, but keeping your body healthy, strong, and fit is generally the best defense, because we are programmed/evolved to resist the pathogens in our environment.