Actually, this from a recent communique from Paul Sigala:
Regarding Richard's comments, he got the details only partially correct. For one thing, this happened on San Gorgonio, NOT in the Sierra (though similar principles likely apply). We camped along the Momyer trail on the south side out of Forest Falls, not far from a stream that crossed perpendicular to the trail (you can find this location easily on any map- it's the first major stream the trail crosses, about 4 miles in). Above the trail the stream heads up towards the crest of the San Bernardino ridgeline without crossing or coming near any other trail. Not believing there were bears there, we left a small pack with some snacks inside in camp and went on a day-hike. Returning several hours later we discovered the pack ripped open and the contents strewn about the campsite (including Jeanette's proud duct-tape velcro chess set that the bear had obviously taken a bite out of!). The bear (mid-sized brown bear) had climbed some small rock ledges along the stream nearby. After several minutes it came down and scurried upstream. This is where the apparent mistake happened. Not minding that the bear had just headed upstream along the stream bed (and pooped in the stream?), I went and filled a 1L nalgene from the stream without treating it. Jeanette took a few sips, while I guzzled nearly the entire liter. Two weeks later J came down with horrific bloating and diarrhea, went to the hospital at UCSD, gave a poop sample, and was told she was "swimming in giardia." She took her Flagyl and was cured within a few days. I on the other hand was asymptomatic, despite having quaffed nearly a liter of the putatively contaminated water. I don't know for sure that J caught it from that water--it just seems the most probable model. I also hypothesized that the bear had pooped in the stream, as animals commonly do when they are frightened and want to lighten their load for a quick escape, without any direct observation that this had indeed happened.
