I didn't have a stool sample taken, so I don't know for sure that I had giardia. It was an assumption, based on that being the first time in my memory of having stomach cramps and pain like that. I don't typically have stomach problems. I had been on the trail for a week, long enough to have gotten giardia even though I was initially treating my water. And, whether or not I had giardia (I do wonder now what else it might have been), I'm still curious to know if the theory fits the people's experience. Thanks for your response!