I get upper respiratory stuff all the time. I have bad allergies, and that makes me more susceptible. I'm an avid hand-washer, and I take vitamins. I do the best I can, but if I come in contact with someone who's sick, I usually get it.
I truly believe some people are more prone to colds and such than others. And if you're not, count yourself lucky and blessed. I do all I can to stay healthy, but the allergies are a curse.