The first ever Progpower held in Chicago, I came home with a nasty cold that settled into pneumonia. Second Progpower I came home unable to speak, voice shot and that settled into a chest cold.
Knock on wood, I've been well the last three PPs. What I do is go to bed early the week before in order to store up my energy. I take a multivitamin daily so I can keep my immune system up (even have my vitamins with me for continental breakfast at the Granada). Keeping my hands clean and the good old hand sanitizer in the purse doesn't hurt at all. Every little bit helps.
Another thing: water, water, water!!!! I drink tons of it while at PP to keep hydrated (all those smokers zap our air of humidity - lol)!
Then I come home and sleep for three days afterward (ha ha)!