I heard the same thing from South American Doctors who deal with parasite problems all the time. Said it takes NUMEROUS stool samples and then you may not catch them. They also said that in North America the labs aren't as good, don't test for as many different species as they do in South America. Said that there are thousands of different species. Said that if you carry the parasite problem back to the states you may NEVER get cured. My ex worked in the Amazon. Everyone got parasites. I got parasites, but never went into the jungle, just the altiplano areas. Had been fighting the problem for years, with no help from U.S. doctors. Really wish I would have stayed in South America where at least I could have gotten proper treatment early on.