Artex said:
Has anyone heard that if you get giardia once, there's a good chance you can't get it again? Any truth to that?
Yes, I think there is a lot of truth to that but in the sense that if you've had it once, you take precautions so that you never get it again. I'm getting to the age where too many of my friends have started to talk mainly about infirmities and illnesses so I generally avoid talking about mine, but here goes on giardia.
I had a case in the early 1980s when I was doing a lot of hiking in the Whites to finish up the "list" trailwrights style, single peak by peak. I was drinking untreated water straight from streams. What I got was not a classic case in the sense that it was low-level, seemingly chronic, would come and go, and could easily be attributed to other reasons (stress, IBS, etc.), none of which sounded right to me becasue I'd never had GI problems before but, hey, I was only the patient. Physicians here had hardly heard of giardia then. It lasted on and off for several years. In the "shedding" stage (which affects the lower colon), it could be intense for a day or so and then eased off, only to build again.
I also noticed a new never-before symptom, lactose intolerance, and assumed that I'd developed that somehow. In the meanwhile, my GI specialist was moving towards a possible diagnosis of colon cancer so we did the drill on that and the test came out negative. He was ready to hang the IBS diagnosis on it and tell me to do some yoga or meditation or whatever to deal with stress, which I was not really under other than this problem.
At about this point I happened to read an article in the ADK magazine, the first I'd seen about giardia in untreated mountain water. It mentioned that giardia can cause lactose intolerance. Bingo, lightbulbs went on, it all came together. To make a long story short, I discussed this with my physician, we treated it with a week of an antiparasitic drug, flagyl, the condition disappeared and has never returned. I have treated water ever since.
Giardia is generally not a big deal if you have a classic full-blown case. It's no fun, but you can treat it quickly and effectively if it presents dramatically. With minimal caution, you can avoid ingesting again. (Wash hands in the backcountry after nature calls as well as treat water.) It's virtually impossible to test for it as it involves getting into the upper intestine, not an easy job. If you have anything other than the classic full-blown case, however, it can be expensive, frustrating, time-consuming, and worrisome to rule out all the really bad things you might have and finally cut to the chase, flagyl or an equivalent drug (there are probably newer and better ones now). Treat or filter the water; in group hiking situations, wash hands before handling food. You can be an asymptomatic carrier and pass it to other people if your hands are contaminated. It's really so much simpler all the way around.