I found this very interesting site on Parasites. It explains why parasites aren't always found in the stool and that you need a mutiple test to find them. Also for those who get dissapointed when not finding any visible signs of parasites - read his story. It's those critters you cant see that cause the most damage. AND they are not easy to get rid of, so keep cleansing...

http://www.badbugs.org/