Backpacker Giardia: The Science and the Evidence

[Colter]

After reading a purportedly scientific paper comparing the risk of giardiasis to the risk of shark attack, I stopped treating all my water and promptly got giardia for the first time in 20+ years.

Having done a lot of research now I've found many major flaws in said paper. I'd be delighted if those of you with a scientific mind would read through my findings and tell me what needs to be changed to make it accurate, or why you think my conclusions are logical as written.

Thanks folks!

[Rasty]

One thing that came to mind first was what the health department defines as an outbreak. Most health departments define an outbreak as two or more non-related persons becoming ill from a common source.

[Colter]

One thing that came to mind first was what the health department defines as an outbreak. Most health departments define an outbreak as two or more non-related persons becoming ill from a common source.

Thanks for the feedback! The definition I quoted is virtually identical to that used by the CDC, who say "outbreak" is synonymous with "epidemic."

Anything else?

[Rasty]

One thing that came to mind first was what the health department defines as an outbreak. Most health departments define an outbreak as two or more non-related persons becoming ill from a common source.

Thanks for the feedback! The definition I quoted is virtually identical to that used by the CDC, who say "outbreak" is synonymous with "epidemic."

Anything else?

Sorry. I'm in agreement with you on the misuse of the word outbreak. If one hiker or a group gets sick it's not an outbreak. If two seperate people or groups gets sick and the only common thing is the water source then it can be an outbreak. Food borne illness works this way.

[Rasty]

Do these scientific studies take dilution into account? The level of giardi in moving water must have a peak right after the fecal matter is deposited in a stream then becomes diluted to safe levels at some point. If this is true then a true outbreak is going to be difficult to define because the health department wouldn't have any evidence to test three or four days latter. Without any evidence the health inspectors I know are going to blame hygiene every time.

[rickb]

The link I followed to the studies you are looking at took me to the abstract, and not the full study-- I probably should have looked harder. I geve up.

After reading a purportedly scientific paper comparing the risk of giardiasis to the risk of shark attack, I stopped treating all my water and promptly got giardia for the first time in 20+ years.

And you were diagnosed with Giardia 2X before going with a filter, correct?

Not sure if your experience applies to the AT, but for where you draw water form and with your resistance to Giardia it seems like the value of a filter is clear cut.

For most peope on the AT, I think it is less so-- but I recognize you could be correct.

Question: What kind of filter have you been using? One of my (minor) concerns with filters would be that they could concentrate giardia in to a critical mass that would eventually leak out in full toxic concentrations.

[Colter]

Do these scientific studies take dilution into account? The level of giardi in moving water must have a peak right after the fecal matter is deposited in a stream then becomes diluted to safe levels at some point. If this is true then a true outbreak is going to be difficult to define because the health department wouldn't have any evidence to test three or four days latter. Without any evidence the health inspectors I know are going to blame hygiene every time.

That's the kind of critical thinking I like. That's an absolutely crucial point that Welch, Rockwell and other skeptics don't factor into their calculations. They repeatedly use averages, but you are exactly right. There are commonly peak points where the water will be loaded with literally millions, often tens of millions of cysts that will eventually be diluted to the point where the water becomes quite safe. Testing results depend on when and where the water is tested and the quality of the testing filters.

It will be extremely difficult to determine if it was dirty hands or bad water a week or two after the cysts were ingested. That's why I believe in restrospective case-control studies like this aforementioned one that studied 256 giardiasis victims and found giardias cases were triple for those drinking untreated water.

[Colter]

The link I followed to the studies you are looking at took me to the abstract, and not the full study-- I probably should have looked harder. I geve up.

And you were diagnosed with Giardia 2X before going with a filter, correct?

Not sure if your experience applies to the AT, but for where you draw water form and with your resistance to Giardia it seems like the value of a filter is clear cut.

For most peope on the AT, I think it is less so-- but I recognize you could be correct.

Question: What kind of filter have you been using? One of my (minor) concerns with filters would be that they could concentrate giardia in to a critical mass that would eventually leak out in full toxic concentrations.

Hi Rick,

You're right, for most of those studies you have to pay to read them. It would be nice if they were in the public domain. There are a few studies linked on my blog that are fully downloadable, including the one I am specifically debunking.

I've pretty much always treated or filtered. The first time I got giardia I have no idea how I got it. The next time I was extremely thirsty fighting a forest fire and drank out of a spring. The next time I was drinking unfiltered Sierra water after having been convinced it was safe to do.

Perhaps this has been linked to many times but it is a large study of AT hikers and unsurprisingly it shows filters and good hygiene both make a difference in hiker health but unfortunately doesn't specifically address giardia.

Every person and every water source is different. I don't mind if people look at the facts and decide not to treat their water.

I've always thought about filters failing and releasing all the baddies at once. Never heard of it but it seems it could happen. I have used filters but currently use Aqua Mira drops.

[10-K]

Saying "I don't treat my water and I've never gotten sick." is like saying "I never wear my seatbelt and never been injured."

But I still don't treat my water...though I am selective.

I do often wonder if you can build up an immunity to the nasties by being exposed to them and building antibodies or whatever...

[rickb]

[QUOTE=Colter;1335869]There are a few studies linked on my blog that are fully downloadable, including the one I am specifically debunking.
QUOTE]

I could't find that one.

[Colter]

[QUOTE=rickb;1335957]

There are a few studies linked on my blog that are fully downloadable, including the one I am specifically debunking.
QUOTE]

I could't find that one.

It's a clickable link in the first sentence. You might have thought it was just a title.

[rickb]

Never mind. Found it.

I like your write up.

But even if one accepts your notion that there is giardia in the backcountry, I am not sure one can conclude that all the different kinds of filters out there -- as used in practice -- really help.

[Snowleopard]

My impression is that there just isn't a lot of hard data. There is no regular testing of backcountry water. I think the methodology of that paper is not reliable; state health departments just don't seem to have much info on backcountry water sources. Most of the data I've seen is data on municipal water systems. Worcester, MA, some time ago had cryptosporidium in its municipal water. Unfortunately for those who advocate just choosing your water sources carefully, most people would judge the Worcester reservoirs about as good as any water source in southern New England. Other municipal supplies have had giardia in the past.

I suspect that most cases of diarrhea on the trail are bacterial but prevention isn't very different whether it's bacteria or giardia or crypto.

In practice, your water treatment needs to eliminate giardia, crypto, bacteria and, in some places, viruses. You also need to be careful of personal sanitation, by hand washing, dish washing, and being careful with bathroom needs.

Most, but not all, filters will filter out both giardia and bacteria. Giardia and cryptosporidium are harder to eliminate with chemicals (long treatment time, even longer with cold water). In practice, if giardia or crypto are possibilities then a good filter, UV (steripen) or boiling are the best choices, or treat with chemicals for a loooong time. A good combination is a filter plus chemicals (possibly just bleach to kill viruses).

[mudhead]

I was not aware that filters work with bacteria.

[Colter]

Never mind. Found it.

I like your write up.

But even if one accepts your notion that there is giardia in the backcountry, I am not sure one can conclude that all the different kinds of filters out there -- as used in practice -- really help.

That might well be true. It's another issue I guess. What I do know for a fact is I made it from 1987 to 2010 treating and being perfectly healthy, and a few weeks after I stopped I had giardiasis! Lots of PCT thru-hikers get giardiasis in the Sierras and it seems that must have some significance.

I'd like to see someone set up a testing program where as many AT and PCT thru-hikers as possible were tested for giardiasis before and after their hikes, and track what types of water treatment methods they used, hygiene habits etc. That would some real data to work with

[Stir Fry]

I do often wonder if you can build up an immunity to the nasties by being exposed to them and building antibodies or whatever...



10K thats a good question, I have never read anything one way or the other. But I do think it true that those that live in Mexico drink the water and don't seem to get sick but you drink when visiting; "Oh my it on" I wander if that could be the reason?

[rickb]

I'd like to see someone set up a testing program where as many AT and PCT thru-hikers as possible were tested for giardiasis before and after their hikes, and track what types of water treatment methods they used, hygiene habits etc. That would some real data to work with

Just googling for Roland Meuser's study (small though it is) and found it summarized in this:

http://erikschlimmer.com/pdf/GiardiaMyth-Buster.pdf

I have no idea where the truth lies, but think everyone should trust their gut on this.

[SouthMark]

I do often wonder if you can build up an immunity to the nasties by being exposed to them and building antibodies or whatever...

I have long wondered the same thing. In 38 years I have never treated or filtered my water while hiking and never been sick. Friends that I know that also do not treat their water and have never been sick like me grew up in rural farming country and frequently drank from streams, creeks, rivers and even ponds. Early water supply was wells on the farm. It probably sounds awful but I and others have drank down stream from cows. Of course we could just be lucky but if that is the case for that length of time and types of water sources I have encountered… I need to head to Vegas immediately.

[Skidsteer]

I have long wondered the same thing. In 38 years I have never treated or filtered my water while hiking and never been sick. Friends that I know that also do not treat their water and have never been sick like me grew up in rural farming country and frequently drank from streams, creeks, rivers and even ponds. Early water supply was wells on the farm. It probably sounds awful but I and others have drank down stream from cows. Of course we could just be lucky but if that is the case for that length of time and types of water sources I have encountered… I need to head to Vegas immediately.

That' my theory as well. I've never known anyone to get giardia that grew up drinking well or cistern water.

No doubt there are exceptions but I haven't found one yet.

[GoldenBear]

The Katadyn Hiker Pro filters down to 0.3 microns
http://www.katadyn.com/usen/katadyn-...o-microfilter/

which will get some bacteria but not viruses, a fact noted by the Center for Disease Control
http://www.cdc.gov/healthywater/drin...treatment.html