One problem with some protozoan parasites like Giardia is the difficulty diagnosing it. Physicians and vets alike will both admit that it's a tough bugger to pin down. It can be there, merrily causing trouble, but it's just hard to find in fecal specimens. And if it's difficult to find where it is specifically suspected, how accurate are those random water tests done on backcountry water sources? Was it not there, or was it there and they just didn't find it?

I don't know about Crystosporidium, but Giardia can infect every kind of mammal there is, it isn't host-specific at all. To me, that means it's endemic in the wildlife, and if there's wildlife where you're hiking, it's there. Maybe not in the particular quart of water you just gathered, but maybe in the next one.

"Better to be safe than sorry" is a very old saying, and there's a reason that it's so old and so well-used.


Sue