This could be a function of your immune system being very efficient. It is impossible to tell whether this is innate (genetic) or a result of your practices (or both). Despite the problems with homeopathic remedies, I find that the placebo effect can indeed be very strong and is often undervalued. Not strong enough to combat something like Ebola, but perhaps strong enough to keep you from contracting a cold or flu when you’re exposed. It also sounds like you practice good hygiene, being mindful of touching surfaces after sick people. So all of this combines to keep you healthy.