All key points, Hygine while in the field is certainly paramount.

Having a dirtbag in the crew certainly don't help. We have a crude name for what you are describing. I won't mention it here but The common slang is simply "gastro". I'm sure nine out of ten times thats all the problem may be. A couple of days with the runs because someone failed to wash their hands and touched your food is not the same as beaver fever. I mean gastro isn't nice either, but it dosen't even rate on the same scale as giardia. Anyone who travels abroad frequently probably picked up "a case of gastro" at least once from eating in an unclean establishment.

When you do get gardia you will know. Takes a week or two IOT develop in most people. Small exposures may not even get to some folks, I have drank directly from water sources many times in the past and almost had to chew the water to swallow it because of all the floaties. Nothing, not even a good fart. but in one particular case we were out for ten days drinking the water we could find as resupply thinking our equipment was working. After drinking that much sheer volume I guess it finally took hold. Knocked me off my feet for a couple of weeks. Another in the party was tested positive later but did not get nearly as sick. If you do react in a less than desireable manner however, look forward to explosive bloody runs, vomiting, severe cramps with chills/fever/skakes and dizziness for 1-2 weeks (with treatment) Not to mention the horrible smell and the embarrasing tests you need to do to confirm your condition at the hospital.

Sorry for the terifying mental images BTW