I take an acidophilus pill every day when travelling. Acidophilus helps your body to fight off invaders in the intestine. In fact, I found a new product that is really good and on the box it recommends you take two a day--one in the morning and one in the evening--when travelling in areas where you feel you might get sick. The brand I use is Culturelle and it's made so that the lacobacillus acidophilus survives the stomach acid and bile so it gets to your intestine in a usable state. You can order it from culturelle.com, if you're interested.

I know it works because of my dog. I take her to a park to play every day. They use reclaimed water to water the grass and it stinks to high heaven. God only knows what sort of germs are in that water. At times, they've watered the grass before we get there, so her rubber ball gets some of that water on it. She had been getting a little diarrhea and I started giving her one of these pills a day. She hasn't gotten the diarrhea ever since I started giving her these pills.