"So what was the purpose of that article except to make the person who wrote it appear smart?"
What's wrong with appearing smart? You got something against smart??

But seriously, I would be happy to convince people to focus more on effective measures (potty hygiene and not sharing dirty cooking pots) than on ineffective measures (water treatment).

As a scientist (physicist, not epidemiologist), it also kind of bugs me when people want to know what's the "purpose" of a scientific fact. What's the "purpose" of tectonic plates, the germ theory of disease, the heliocentric model of the solar system, or Mendelian genetics? They are what they are. We shouldn't have to apologize for them.

Edited by bcrowell on 02/25/2011 19:37:00 MST.

Ben, you have so much focus on potty hygiene that maybe you need to look in the mirror.

Most of the rest of us don't have a problem with it.

--B.G.--

"Ben, you have so much focus on potty hygiene that maybe you need to look in the mirror. Most of the rest of us don't have a problem with it."
Bob, let's focus on the science and avoid the ad hominem attacks.

Ben is arguing his case respectfully. We should all do the same in the tradition of Backpackinglight, one of the last bastions of internet civility.

Ben, I could focus on science, but I haven't found very much here yet.

Some of us have been doing the lab tests for the last 35 years or so.

--B.G.--

I'm much more concerned about crypto (which can kill you) or blastocystis (which doesn't get killed by much of anything)

I've had the same blastocystis infection for over 20 years. It continues to change my life in limiting ways. While the indigenous blasto to n. america is milder than the zoonotic variety I picked up in Taiwan, there are more and more infected people returning or coming to n. america from other places, increasing the prevalence of other strains here. This sh*t is almost impossible to kill--i've been through numerous treatments. Typical chlorine treatments won't usually kill blasto, but a good filter or boiling will work.

Blasto is one of the most common parasites--much more prevalent than giardia. Fortunately for most here, the strain native to the USA usually doesn't cause any symptoms, but some of the other strains (which are genetically unique enough to actually be classified as separate species) are highly symptomatic and are increasing in USA. If you go anywhere tropical, there are likely several different blasto strains in virtually any water.

The famous Welch paper says Forty-eight of the 50 state health departments in the United States responded to a questionnaire about giardiasis in their jurisdictions. The agencies had reports of 34348 cases during 1991 and studied 80 outbreaks in the same period. Nineteen of these outbreaks were attributed to consumption of contaminated drinking water; only two outbreaks were reported among individuals identified as campers or backpackers. http://www.ncbi.nlm.nih.gov/pubmed/11995903

Following is my attempt to look at these numbers in a different, and what I think is a more telling, way.

The CDC estimates there are an upwards of 2.5 million cases of giardiasis annually in the U.S. http://www.giardiasis.org/

Using the 2-7% infection rate for developed countries would actually mean there are a minimum of 6,680,000 cases a year. But we'll take the lowest number of 2,500,000 cases, of which 34,348 were reported in 1991. 2,500,000 - 34,348 = 2,465,652 unreported cases. That means about 98.6% of cases go unreported. That figure supports what many physicians say, they usually don't report Giardia.

A disease outbreak is defined as "the occurrence of cases of disease in excess of what would normally be expected in a defined community, geographical area or season." Thus, in 1991 there were only 80 outbreaks reported, or at least studied, out of 34,348 reported cases.

Now by my reasoning there would be a lot more reported outbreaks around large numbers of people sharing the same food and water (swimming pools, day care centers, rest homes etc,) if so the ratio of outbreaks/vs individual cases would skew towards the under reporting of individual backpacker Giardia, regardless of source. But we'll go with the low numbers again. Out of 80 actual outbreaks total, 2 were reported from contaminated drinking water from campers and backpackers. That's 2.5%.

If 2.5% of national Giardia cases are caused by camper/backpacker drinking water (2.5% times 2.5 million) that's 62,500 cases a year, minimum, of campers/backpackers contracting Giardia from contaminated water, extrapolating from the official numbers.

Now I grant there are some fuzzy numbers in there, but I think they are a lot more representative of the truth than this quote, based on the same fuzzy base numbers and used over and over again in literature attempting to promote the "myth" of getting giardia from backcountry drinking water: Nineteen of these outbreaks were attributed to consumption of contaminated drinking water; only two outbreaks were reported among individuals identified as campers or backpackers. That number of 62,500+ sounds a lot different than 2.

Check my numbers. If I've made any errors point them out and I'll make the changes.

Buck, I think you are going to have a really tough time getting your arms around hard statistics on this. Part of the reason is that self-selection is going on. Some backpackers who consume contaminated water will get acute symptoms, some will get mild symptoms, and some will get no symptoms at all that they recognize. Some may get a transient bout of mild symptoms and then just chalk it up to some food that went bad, and they might not realize that they've become a carrier. If you stood at some appropriate trailhead and interviewed backpackers coming out, and if you asked them if they had any giardia symptoms, probably nearly 100% would report a negative, even if they had been on the trail for weeks. Probably only the backpackers with acute and recurring symptoms will actually seek out a physician for treatment. This is totally impractical, but it would be different if everybody coming off the trail had to be lab tested. Then you could begin to get some real statistics.

At one point in time a few years ago, California State University - Fresno was doing research into "backcountry health." I don't know how extensive they got, but I remember part of their interview process.

--B.G.--

I absolutely agree, Bob. There's just not enough dependable hard data. But the point is that the numbers we have are being spun in misleading ways or at the very least are being used to draw sweeping conclusions based on incomplete data.

The supporting evidence for not treating backcountry water is presented in five logical, myth-busting arguments http://www.erikschlimmer.com/pdf/GiardiaMyth-Buster.pdf

In my opinion the data mining done in that article is egregious.

"Now by my reasoning there would be a lot more reported outbreaks around large numbers of people sharing the same food and water (swimming pools, day care centers, rest homes etc,)"

I've heard this before, and it poses an interesting epidemiological question: Most water used in urban settings is treated and, therefore, not infested with giardia, so how does it get into swimming pools, day care centers, nursing homes, etc? What are the vectors? Clearly they exist, but what are they? Certainly not backpackers alone. People returning from abroad? Pets? Urbanized wild critters pooping on lawns and kids or pets picking it up? Has anybody read of studies addressing tis?

Tom, most water used in urban settings is treated and probably not infested with high risk of giardia. It is probably low risk, but it may not be zero risk.

It doesn't take much imagination how swimming pools become contaminated, nor day care centers, nor nursing homes.

--B.G.--

A one-year retrospective laboratory survey in Colorado revealed that 691 (3%) of 22,743 stool examinations for ova and parasites were positive for Giardia lamblia, a higher percentage than that reported from surveys outside of Colorado. The majority of infected residents who were surveyed had experienced an episode of chronic watery diarrhea (median duration 3.8 weeks) with bloating, flatulence, and weight loss (averaging 5.1 kg), and had responded to a course of metronidazole or quinacrine. A statewide telephone survey of 256 cases and matched controls identified: 1) and increased incidence of giardiasis in persons between the ages of 16 and 45, p less than .001, with males and females equally affected; and 2) a higher proportion of cases than controls who visited Colorado mountains (69% vs. 47%), camped out overnight (38% vs. 18%), and drank untreated mountain water (50% vs. 17%), p less than .001. Also identified was a correlation between the seasonal distribution of cases and degree of fecal contamination of mountain streams. These results indicated that G. lamblia is endemic in Colorado and that drinking untreated mountain water is an important cause of endemic [giardia]infection.

Reality trumps theory.

http://www.journals.elsevierhealth.com/medline/record/ivp_00029262_105_330

Edited by Colter on 02/27/2011 21:10:01 MST.

I knew there was a lot of confusion about treating/filtering water, but I have never seen it put so clearly. Thanks for sharing.

I'm not a research scientist so I don't really understand the numbers. But is the fact that Colorado residents are more likely to venture into the backcountry than most (not all) states residents taken into consideration when they say it? I moved here from California and the % of residents who are outdoor enthusiasts is much higher. That's a big reason we move here. Sorry if I don't understand the numbers correctly. I'm just curious.

Randy, I'm not a research scientist either, but here's what I would say:

The specific numbers are unimportant. The study only deals with cases of Giardia confirmed by laboratory. It shows that persons drinking untreated mountain water are much more likely to get Giardia than those that don't. The state will not be the primary factor, but rather the presence of Giardia.

That given, giardia occurs nationwide and is common in California. The Sierra Nevada is considered one of the most high risk areas in the U.S. http://emedicine.medscape.com/article/782818-overview. Perhaps no coincidence that that's where PCT thru-hikers tend to get sick.

Couldn't most of this debate be solved if some researchers went out backpacking and actually sampled a number of water sources for these various organisms?

Mary, that has been done. However, to do a really good job of it, the whole project will be very expensive. Do you want your tax dollars to go for that?

Twenty-five years ago the diabetics did not have small blood glucose meters, and then there was enough demand that they are common now. Wouldn't it be neat if backpackers had some kind of similar size "bug meter" that could be dipped into a stream, and then 30 seconds later an indicator said "safe" or "risky" or something else?

I would not hold my breath waiting for that to happen.

--B.G.--

"It doesn't take much imagination how swimming pools become contaminated, nor day care centers, nor nursing homes."

If I really work at it I can imagine that, Bob. What I'm getting at is: where do the people that crap in the pools, etc, pick it up? They're not all backpackers, and the water they drink here in the US of A is supposed to be adequately treated, so how do they vector it in? Travel abroad? Contaminated municipal water systems? Agricultural workers bringing it into the lettuce fields and then practicing poor potty hygiene? One or more of the above? If other, what specifically?

"where do the people that crap in the pools, etc, pick it up?"



Perhaps they picked it up in the very same pool two weeks before.

Or, in the case of a day care center... little kids are notoriously unclean when they are outside of the watch of their mothers. The carpet probably needs to be hosed down twice a day.

Some of our oldest senior citizens have a problem with this also.

Agricultural workers are more likely to be in a situation where they can't afford proper medical care. They think they got into some bad food, and the symptoms will pass... but it hits them at the worst time.

--B.G.--

One thing I've found out is that the "10 cysts for an infectious dose" quotes seen in many papers all trace back to a single limited study. I am interested in having some of you look at this chart and tell me what you think? For example, what would the chances of infection be if someone drank 5 giardia cysts, based only on that chart?

The full study is Waterborne Transmission Of Giardiasis Proceedings Of A Symposium Held At Cincinnati Ohio On Sept 18-20, 1978 starting on page 64. For some reason I couldn't link it.

Bob Gross, could you PM me or contact me through my website? Thanks!

Edited by Colter on 02/28/2011 22:40:23 MST.