North of Sonora. Does hiker hygiene go down on certain parts of the trail, or would it be because there's more Giardia in the water on that stretch of trail? That is the stretch where PCT hikers tend to get Giardia, isn't it?
I absolutely agree about anecdotal evidence and my story proves nothing standing on it's own. But most articles like what I wrote start with a personal lead-in. My story about believing the "debunkers," then not treating, and subsequently getting Giardia is about as relevant as it gets. I think the rest of my manifesto stands on it's own, with two scientific studies concluding hikers are getting giardia from drinking water.
I read the Derlet article. If you read a skeptical article about the dangers of giardiasis, they will likely be written by, or sourced to, Delret, Welch, Zell, or Rockwell, who in turn usually source each other. I think Zell is the most objective and has come closest to doing what needs to be done. Actually, it might not even be fair to call him a skeptic.
No one is ever going to prove whether hikers are getting Giardia from testing a few dozen sites and trying to extrapolate the results to all other untested water sources. For one thing, they never seem to take into account that any time you have one Giardia cyst that there were likely MILLIONS in a concentrated area when they first entered the water. Derlet himself said on REI.com Here's a fact I recently uncovered: Giardia-infected cattle excrete nearly 100 million Giardia cysts per day, and pack animals excrete about 12 million per day. Twelve million! So be careful if you drink in those watersheds. Well, jeez, thanks! I read that after I was convinced that it was paranoia to drink the water untreated in the Sierras. As I've related, my best guess is I got Giardia from a place where cattle had been grazing. Hadn't run across cattle grazing in probably a month. Didn't know they were there until after I drank. Of course, infected people excrete up to 10 BILLION a day.
What needs to be done is more extensive studies like Zell's to determine who is getting Giardia, and HOW they got it. Zell tested the hikers before and after in the Desolation Wilderness study. Between 5 and 8% or so got Giardia on their Sierra trip, except it didn't determine how they got it.
Seems to me some much larger, more carefully controlled studies like this informal poll could really help to paint a picture of what's going on: http://forums.outdoorsdirectory.com/showthread.php/94691-Giardia-Poll-Please-vote!/page2 The Colorado study I talked about on my blog where 3 times as many untreated-water drinkers got Giardia was good, because they studied 691 people who actually HAD laboratory confirmed Giardiasis. Less theories and more new research. Find out what actually DID happen and WHY.