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Giardia question
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Elizabeth Tracy
(mariposa) - M

Locale: Outside
Giardia question on 09/29/2011 14:05:05 MDT Print View


I use my coffee mug, or a little plastic cup, to scoop water from which to fill my Platypus bags. (In most locations it is impossible to fill up the narrow-top Platy bags without a scooper.) I then treat the Platy water with Aquamira.

But then I use my mug/cup to drink out of. This could be a hot drink at breakfast/dinner; and/or making a cold electrolyte-mix drink midday.

Am I being stupid about giardia? Aren't there going to be giardia cysts hanging out in the cup/mug after it's been used as a scooper? Can those cysts be wiped away with a cloth, UV-exposured away (by drying the mug in the sun), or boiled away (by pouring boiled water into the mug)?

- Elizabeth

Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: Giardia question on 09/29/2011 14:16:22 MDT Print View

Hi Elizabeth,

To play it straight, you'd consider the cup or mug contaminated after using it as a raw water scoop, possibly from giardia cysts or more commonly, from bacteria. You could rinse it with treated water and either shake it dry or wipe it with a clean cloth to greatly reduce any contamination. If the cup is metal, you could sterilize it by passing it over a stove flame, even briefly. I remmeber doing that in micro lab in school, only over a bunson burner, not a camp stove.

IMHO if it's worth treating the water, it's worth taking this extra step as well. Either that or have a dedicated scoop. Some folks fashion very light ones from plastic water bottles.



ben wood

Locale: flatlands of MO
Re: Giardia question on 09/29/2011 15:05:19 MDT Print View

hey, here's a thought.

take a platy bottle, cut off the bottom so that it is kinda like a funnel and use that as a water "scoop". It will weigh less than 1oz and can be your dedicated water scoop thingy.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Giardia question on 09/29/2011 16:12:30 MDT Print View

> Aren't there going to be giardia cysts hanging out in the cup/mug after it's been used as a scooper?

Well, maybe. Let's imagine there are 100 cysts per litre of water - that is an absurdly HIGH loading, btw for a running creek. The water left on your cup might amount to 0.5 cc, or 0.005 L. Then your cup should have 0.5 cysts attached to it. Now shake the cup or wipe it dry, and you are down to <0.1 cc or < 0.001 L. That amounts to 0.1 cyst.

Also remember that it takes about 10 cysts for you to become infected.

In short, the probability of any harm is so close to zero you would be better off worrying about tripping over your own feet and falling in the creek.


Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Giardia question on 09/29/2011 16:15:23 MDT Print View

"In short, the probability of any harm is so close to zero you would be better off worrying about tripping over your own feet and falling in the creek."

But I have fallen into the creek!

You make the assumption that the giardia cysts are distributed evenly through the raw water.


Buck Nelson
(Colter) - MLife

Locale: Alaska
Very low probability, but not zero. on 09/29/2011 18:25:54 MDT Print View

The ten giardia cyst minimum for infection is oft-repeated, even by experts, but comes from a misinterpretation of a single, very limited study. I think this statement is much closer to the truth: one (giardia) cyst has a 2 percent probability of causing giardiasis

I always treat my drinking water but, wisely or not, don't worry a whole lot about contamination from tiny amounts of untreated water.

Edited by Colter on 09/29/2011 18:28:26 MDT.

Sumi Wada
(DetroitTigerFan) - F

Locale: Ann Arbor
Re: Giardia question on 09/29/2011 19:28:50 MDT Print View

Logically, it's obviously not good practice to use your drinking cup as the water scoop. That said, I can't imagine that your exposure is any worse than going swimming in lakes/rivers or rinsing your face in a stream. I think we all do those things without worrying.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Giardia question on 09/29/2011 20:02:02 MDT Print View

It is good practice to treat every drop of water as if it might make you sick. It is good protocol, because you never know when some raw water might be unavoidable. I don't like to get too paranoid about it, but if it is convenient to practice safety down to the drop, you might as well.

Many years ago while I was in military training, there was very poor water management in the field, and I got sick. The physician thought that it was from something in the water, but we didn't even talk about Giardia in those days.

I would rather be safe than sorry.


Ryan Krause

Locale: Pacific Northwest
My take on 09/29/2011 20:48:41 MDT Print View

The 10 cyst minimum comes from a 1953 study - I've never seen it in full but it is still referenced by the CDC and they themselves quote the 10 cyst minimum in their giardia literature. However the sample size was quite small, and replicating such a trial today may be impossible to conduct such a trial due to ethics - this study and a similar 1913 trial recruited prison inmates that gave informed consent.

10 cysts or not, my personal take is the risk is low from backcountry water - the greater risk is from other people you share food with that have poor hygiene or you yourself have poor hygiene. Washing hands and keeping clean are very important.

Risk of giardiasis from consumption of wilderness water in North America: A systematic review of epidemiologic data

Few years back there was a good article here on BPL by Dr. Gortler on water sourcing to minimize risk:

Buck Nelson
(Colter) - MLife

Locale: Alaska
Re: My take on 09/30/2011 09:36:01 MDT Print View

Ryan, could you source that 1913 giardiasis infection study? The only study I could find is reflected in these results:Infectious Dose Study for Giardia

As you can see, 60% of the men contracted giardiasis with 10 or more cysts. Below the 10 cyst level, only 5 people were tested ONCE, and with a single cyst. There were no tests run at the 2-9 cyst level. There was a 100% infection rate at the 10 cyst level. The sweeping conclusion that there is a 10 cyst minimum required for infection simply makes no sense.

The Welch study you cited I find misleading to the extreme. He studies Giardiasis outbreaks. Backpacker giardiasis will very rarely qualify as an outbreak. In 1991 there were only 80 [giardiasis] outbreaks reported nationwide, or at least studied, out of 34,348 reported cases, out of an estimated 2,500,000 ACTUAL giardiasis cases. His insinuation that because there are few giardiasis outbreaks reported that giardiasis in backpacking must be rare is a major logical fallacy.

As I've said before on this forum, on the PCT in 2010 I wasn't treating my drinking water on the advice of people like Welch. When I went into Mammoth Lakes to be treated for giardiasis, my physician laughed when I told him about those studies such as Welch's, saying he treats backpackers for giardiasis very frequently.

My giardiasis manifesto is here. I welcome any feedback on it.

Rick Dreher
(halfturbo) - MLife

Locale: Northernish California
Re: My take on 09/30/2011 10:20:21 MDT Print View

I'll caution that giardia is unlikely to be present by itself; bacteria are almost certain to be present as well--the only question is whether any are pathogenic. Giardiasis is quite possibly overemphasized as a waterborne pathogen and because it's hard to diagnose and there's a significant time lag between exposure and active case, we're unlikely to ever have decent emperical data.

My take: do not design your water protocol completely around giardia.



Elizabeth Tracy
(mariposa) - M

Locale: Outside
Keep 'em coming on 09/30/2011 11:58:41 MDT Print View

Great discussion.
The debate is useful.
What else do people do? A dedicated scoop? Use your cup but dry it or sanitize it?

Craig W.
(xnomanx) - F - M
Giardia question on 09/30/2011 12:18:18 MDT Print View

If I worry about and treat giardia on the threads of my water bottle or inside a wiped-out, now dry coffee mug, it would stand to reason I should I gargle chlorine dioxide after opening my mouth and disinfect my lips after swimming in a mountain lake.

Should I just keep my head above water when I swim?

But then should I treat my hands after touching mountain water before I eat or put them in my mouth?


Volume folks, volume.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Keep 'em coming on 09/30/2011 12:58:25 MDT Print View

I never use any water scoop. A few days ago I was in a place where the spring water was just a dribble down a hillside. I placed a few rocks into the water to make a tiny dam about an inch high. Where the water poured over the dam is where I aimed my Platypus opening.

If I were forced to use a mug to gather water, that would be OK. I would dry out the mug with my shirt tail until it was dry, then let it air out. If I thought there could be any residual moisture left in the mug, then either it would be placed over the stove for a few seconds or else filled up with boiling water.

What I mean is that superhuman precautions are probably unnecessary, but it doesn't hurt to use the precautions that are convenient or quick.

Years ago, back when we were still treating our water with iodine solution, I used to rinse out a contaminated mug with a concentrated iodine solution. But then, where do you dispose of such a powerful solution?

As a backpacker, I have never gotten sick from the water. Some of my friends on the same trips were less cautious, and they have gotten sick and were diagnosed by a doctor.