My best friend's brother was a (nearly) OCD germaphobe for quite some time. He was very careful about washing his hands and such. He didn't get sick often, but when he did, he got very sick. And no one else around him, not even his family, got very sick when he did. Nothing like that had ever happened to him before (where he got very sick but his family did not). While it is not very strong evidence, nor is it scientific, I believe that it was because the lack of exposure to bacteria and the like weakened his immune system and left him more susceptible to bugs that a normal immune system would be able to fight off without incident.

Interestingly, it seems that all parties concerned experience the same amount of "sick," it's just a question of duration and severity. Personally, I think I'd rather be a bit under the weather for a while than incapacitated for a few days.