I found a web page with many frustrated patients who had bad experiences with ignorant and arrogant doctors: www.badbugs.org/LabTesting.htm

How do you like this microbiologist's response to a sick person:

"Well, you can make your symptoms match any disease you want to, can't you?"

One of the most interesting and perhaps important claims of that page is that one test is likely to catch only 50% of the parasites. Ten tests are expected to catch 95%. One patient had Giardia diagnosed only after 8 samples.