That's a great story, and it sounds like an amazing trip.

It's not a "will", it's a "might". It's a game of Russian roulette; 5 times you might be fine, but is it worth it if the 6th isn't, and you spend the rest of the vacation puking and crapping your guts out?

For me, the question is: are there any such parisites in the Alps? Maybe not. Giardia in the new world is spread largely by beavers, as I understand it, and those don't exist (much) anymore in Europe.