Just a day after posting the previous comment, a couple of very pertinent publications came out.
First of all, Wilderness and Environmental Medicine, a wilderness medicine peer-reviewed journal, published a case report of a hiker in the Grand Canyon who appeared to have died from complications of hyponatremia. She was a 47 year old otherwise healthy woman, who hiked about 10 kg, and was described as drinking "a large amount of water." She had a rapid deterioration in neurologic status, and had findings of brain swelling. Her serum sodium concentration when measured in the hospital was lowish, although not as low as one would have expected from the description of her medical event. She had, however, been receiving some intravenous fluid prior to reaching the hospital.
I am not totally convinced by this case report, largely because of missing data, but the explanation is plausible. In any case, it is a reminder of what I said earlier: If one is not thirsty, don't drink!
(This article is not yet available online, but the citation is Wild Environm Med 2015;26:371-374.)
A second article, actually much more interesting, was also published in the New York Times:
http://www.nytimes.com/2015/08/25/upshot/no-you-do-not-have-to-drink-8-glasses-of-water-a-day.html?_r=3&abt=0002&abg=0
This article, by a physician, reviewed the recent emphasis on increasing water drinking and subtle dehydration and found it bogus. He reiterated the importance of paying attention to one's own thirst mechanism.
Friday, September 11, 2015
Wednesday, September 2, 2015
Can water be bad for you?
I am not talking here about water borne illness--anyone reading my publications or blog posts knows my feelings about that! I am, instead, focusing on problems related to the over-consumption of water from any source. Believe it or not, this is actually a growing problem. It was nicely reviewed recently in an article in the New York Times:
http://well.blogs.nytimes.com/2015/08/26/for-athletes-the-risk-of-too-much-water/?_r=0
The physiology here is actually quite simple. When water is added in excess to the body, it dilutes the amount of sodium in the circulation, a condition called "hyponatremia." Hyponatremia can cause a host of complications, including devastating and occasional fatal brain injury.
Fortunately, the body has a couple very effective mechanisms to prevent over-consumption of water. The first is our thirst mechanism. Once one has drunk enough water to result in even very minimal hyponatremia, our thirst shuts off and there is simply no desire to drink any more. Secondly, the kidneys are very good at excreting excessive water; this is why your urine looks so clear after drinking a lot of fluid.
Dangerous hyponatremia can result if we consistently over-ride our thirst mechanism and/or if the ability of the kidney to excrete excess water is impaired. Vigorous athletic activity can result in both of these. Hormones produced during exercise may impair kidney water excretion, and admonitions to drink heavily during sport may push us even when our thirst says "no more!"
Most of the reports of this condition have been during endurance sports such as marathon running. I have not heard of well-documented cases occurring during conventional backcountry travel or hiking.
One of the lessons of this subject is the importance of listening to one's body. Fear of dehydration has often led to the admonition for athletes to drink even if they are not thirsty. This is probably a mistake. Mild dehydration may impair athletic performance a bit (although even that is debatable), but is rarely fatal. Probably the best advice is simply pay attention to one's feelings. If you are thirsty, drink. If you aren't, don't.
http://well.blogs.nytimes.com/2015/08/26/for-athletes-the-risk-of-too-much-water/?_r=0
The physiology here is actually quite simple. When water is added in excess to the body, it dilutes the amount of sodium in the circulation, a condition called "hyponatremia." Hyponatremia can cause a host of complications, including devastating and occasional fatal brain injury.
Fortunately, the body has a couple very effective mechanisms to prevent over-consumption of water. The first is our thirst mechanism. Once one has drunk enough water to result in even very minimal hyponatremia, our thirst shuts off and there is simply no desire to drink any more. Secondly, the kidneys are very good at excreting excessive water; this is why your urine looks so clear after drinking a lot of fluid.
Dangerous hyponatremia can result if we consistently over-ride our thirst mechanism and/or if the ability of the kidney to excrete excess water is impaired. Vigorous athletic activity can result in both of these. Hormones produced during exercise may impair kidney water excretion, and admonitions to drink heavily during sport may push us even when our thirst says "no more!"
Most of the reports of this condition have been during endurance sports such as marathon running. I have not heard of well-documented cases occurring during conventional backcountry travel or hiking.
One of the lessons of this subject is the importance of listening to one's body. Fear of dehydration has often led to the admonition for athletes to drink even if they are not thirsty. This is probably a mistake. Mild dehydration may impair athletic performance a bit (although even that is debatable), but is rarely fatal. Probably the best advice is simply pay attention to one's feelings. If you are thirsty, drink. If you aren't, don't.
Thursday, December 11, 2014
Ebola in the Wilderness
Yup. You read that right.
It was bound to happen.
With all the hullabaloo in the media about the risk of Ebola taking hold in the US "homeland", it was only a matter of time before some started fretting about a participant in an organized camping program or wilderness trek developing the disease.
Over the past few weeks, I have had emailed questions, participated in a discussion regarding the agenda at an upcoming outdoor education meeting, and attended a council meeting--all of which involved the question of whether outdoor education programs should have contingency plans for Ebola.
Gimme a break!
There is no questioning the fact that Ebola is a monumental crisis, a health problem of unimaginable severity with the potential for destabilizing a huge part of Africa. Its victims die horrible deaths.
Having said that, Ebola will never be anything more than a blip on the screen of health problems in developed areas such as the US. Its spread depends upon living conditions, health care practices, and severe poverty. As the past few months have shown, despite some well-publicized imported cases, the disease simply has not taken hold--exactly as the experts (decried by politicians, of course) predicted. I wrote a piece about this in the Syracuse newspaper:
http://www.syracuse.com/opinion/index.ssf/2014/10/great_ebola_epidemic_if_decency_wont_prompt_aid_maybe_self_interest_will_your_le.html
There are plenty of things to worry about regarding Ebola, but someone coming down with it in a tent in the North American backcountry is not one.
As much as I would like simply to laugh this off, there are two things about this which really bother me.
The first is the pitifully narcissistic way in which we look at threats. Rather than worrying about the fate of hundreds of thousands of unfortunates living in daily fear of this disease, we argue about how it should be handled in US airports. Rather than aiding local health care workers in areas which are dealing with Ebola every day, we corner the market on protective gear to be stored in hundreds of American hospitals which will never see a case. "Just in case."
The second is a theme which runs through a lot of my writings on wilderness health and safety. What is it that seems to cause some wilderness educators to become infatuated with "problems' which are either nonexistent or trivial (wilderness water quality, Ebola), while ignoring issues of demonstrably greater importance (immunizations, hand sanitation)?
Go figure.
It was bound to happen.
With all the hullabaloo in the media about the risk of Ebola taking hold in the US "homeland", it was only a matter of time before some started fretting about a participant in an organized camping program or wilderness trek developing the disease.
Over the past few weeks, I have had emailed questions, participated in a discussion regarding the agenda at an upcoming outdoor education meeting, and attended a council meeting--all of which involved the question of whether outdoor education programs should have contingency plans for Ebola.
Gimme a break!
There is no questioning the fact that Ebola is a monumental crisis, a health problem of unimaginable severity with the potential for destabilizing a huge part of Africa. Its victims die horrible deaths.
Having said that, Ebola will never be anything more than a blip on the screen of health problems in developed areas such as the US. Its spread depends upon living conditions, health care practices, and severe poverty. As the past few months have shown, despite some well-publicized imported cases, the disease simply has not taken hold--exactly as the experts (decried by politicians, of course) predicted. I wrote a piece about this in the Syracuse newspaper:
http://www.syracuse.com/opinion/index.ssf/2014/10/great_ebola_epidemic_if_decency_wont_prompt_aid_maybe_self_interest_will_your_le.html
There are plenty of things to worry about regarding Ebola, but someone coming down with it in a tent in the North American backcountry is not one.
As much as I would like simply to laugh this off, there are two things about this which really bother me.
The first is the pitifully narcissistic way in which we look at threats. Rather than worrying about the fate of hundreds of thousands of unfortunates living in daily fear of this disease, we argue about how it should be handled in US airports. Rather than aiding local health care workers in areas which are dealing with Ebola every day, we corner the market on protective gear to be stored in hundreds of American hospitals which will never see a case. "Just in case."
The second is a theme which runs through a lot of my writings on wilderness health and safety. What is it that seems to cause some wilderness educators to become infatuated with "problems' which are either nonexistent or trivial (wilderness water quality, Ebola), while ignoring issues of demonstrably greater importance (immunizations, hand sanitation)?
Go figure.
Wednesday, June 4, 2014
Silly science and the drinking of urine
A friend sent me the following link, having remembered my outdoor education comments that urine was generally sterile, and did not require any particular precautions in the backcountry:
http://www.outsideonline.com/news-from-the-field/Your-Pee-Isnt-Sterile.html
There are two parts to this story, one which is simply a bad interpretation of mediocre science and the other of which is a genuinely stupid concept which seems to have some traction.
First things first: the bad interpretation of mediocre science.
The article refers to a study presented at a recent medical meeting which actually had nothing to do with the outdoors; it was a study of the urine of women with overactive bladder. The investigators used what was described as a "cutting edge" method to show that most urine contained bacteria, even if this could not be shown by the conventional method (growing actual bugs from the urine). The method (hardly "cutting edge"--it's been around for years) actually involved identifying not bacteria themselves but rather traces of their genetic material, DNA. This is the same methodology which is used in forensics to identify suspects from traces of their body fluids.
What the investigators actually showed, therefore, was not that bacteria were present in some urine samples but that traces of bacterial DNA were present. There is a big difference. This method is so sensitive that it can identify the most miniscule of traces of bacterial DNA. Such material is probably all around us--any living thing can leave such "fingerprints".
When we talk about something being "sterile", we do not mean the absence of tiny amounts of genetic chemicals. We mean the absence of viable bacterial which can grow according to usual laboratory methods. Isolated fragments of DNA cannot reproduce, grow, or cause disease. Thus, the absence of bacteria growing in standard culture from urine indicates that the urine is "sterile", in spite of any "cutting edge" DNA findings.
So, the thoughtful, environmentally sensitive camper can continue to relieve himself or herself in the North American wilderness without fretting about spreading disease. Some have argued that the concentrated salts of urine could have unpleasant environmental consequences, damaging flora or attracting animals. This may or may not be a concern. If it is, however, there is an easy solution: pee in streams or other bodies of water! Heresy, eh?
Now for the genuinely stupid concept.
Apparently, there is a thread in some circles which promotes the drinking of urine as a health or survival technique. According to the Outside article, the media's favorite spokesperson for this is apparently a dude named Bear Grylls, who has some sort of reality show Man versus Wild. In one segment, he is shown in a very hot, dry desert, extolling the benefits of drinking urine as a way of maintaining hydration.
The Outside article used the above study showing urine was "unsterile" as a way of criticizing Grylls. The problem with the technique, however, has nothing to do with sterility. It shows an incredible lack of understanding of basic human physiology.
The role of urine is to concentrate and excrete salts in the diet as well as the break down products of protein digestion. Drinking urine may supply one with some water, but it also puts right back into the body the salt and waste products which are contained in the urine. These have to be excreted again, but will require more body water in order to make the urine to excrete them a second time. Thus, drinking urine actually worsens dehydration, even though it puts a bit more fluid into the body.
This is pretty basic science. It was shown most elegantly by a chap named James Gamble, who in the 1940s did very careful studies designed to create the optimal life raft ration. Taking anything other than plain water clearly made one's hydration worse. Of course, it was "reported" even earlier by Samuel Taylor Coleridge in The Rime of the Ancient Mariner: "Water, water everywhere, but not a drop to drink."
I guess that Bear Grylls doesn't read romantic English poetry.
http://www.outsideonline.com/news-from-the-field/Your-Pee-Isnt-Sterile.html
There are two parts to this story, one which is simply a bad interpretation of mediocre science and the other of which is a genuinely stupid concept which seems to have some traction.
First things first: the bad interpretation of mediocre science.
The article refers to a study presented at a recent medical meeting which actually had nothing to do with the outdoors; it was a study of the urine of women with overactive bladder. The investigators used what was described as a "cutting edge" method to show that most urine contained bacteria, even if this could not be shown by the conventional method (growing actual bugs from the urine). The method (hardly "cutting edge"--it's been around for years) actually involved identifying not bacteria themselves but rather traces of their genetic material, DNA. This is the same methodology which is used in forensics to identify suspects from traces of their body fluids.
What the investigators actually showed, therefore, was not that bacteria were present in some urine samples but that traces of bacterial DNA were present. There is a big difference. This method is so sensitive that it can identify the most miniscule of traces of bacterial DNA. Such material is probably all around us--any living thing can leave such "fingerprints".
When we talk about something being "sterile", we do not mean the absence of tiny amounts of genetic chemicals. We mean the absence of viable bacterial which can grow according to usual laboratory methods. Isolated fragments of DNA cannot reproduce, grow, or cause disease. Thus, the absence of bacteria growing in standard culture from urine indicates that the urine is "sterile", in spite of any "cutting edge" DNA findings.
So, the thoughtful, environmentally sensitive camper can continue to relieve himself or herself in the North American wilderness without fretting about spreading disease. Some have argued that the concentrated salts of urine could have unpleasant environmental consequences, damaging flora or attracting animals. This may or may not be a concern. If it is, however, there is an easy solution: pee in streams or other bodies of water! Heresy, eh?
Now for the genuinely stupid concept.
Apparently, there is a thread in some circles which promotes the drinking of urine as a health or survival technique. According to the Outside article, the media's favorite spokesperson for this is apparently a dude named Bear Grylls, who has some sort of reality show Man versus Wild. In one segment, he is shown in a very hot, dry desert, extolling the benefits of drinking urine as a way of maintaining hydration.
The Outside article used the above study showing urine was "unsterile" as a way of criticizing Grylls. The problem with the technique, however, has nothing to do with sterility. It shows an incredible lack of understanding of basic human physiology.
The role of urine is to concentrate and excrete salts in the diet as well as the break down products of protein digestion. Drinking urine may supply one with some water, but it also puts right back into the body the salt and waste products which are contained in the urine. These have to be excreted again, but will require more body water in order to make the urine to excrete them a second time. Thus, drinking urine actually worsens dehydration, even though it puts a bit more fluid into the body.
This is pretty basic science. It was shown most elegantly by a chap named James Gamble, who in the 1940s did very careful studies designed to create the optimal life raft ration. Taking anything other than plain water clearly made one's hydration worse. Of course, it was "reported" even earlier by Samuel Taylor Coleridge in The Rime of the Ancient Mariner: "Water, water everywhere, but not a drop to drink."
I guess that Bear Grylls doesn't read romantic English poetry.
Tuesday, August 27, 2013
What can they be thinking?
The following item caught my attention recently:
http://www.huffingtonpost.co.uk/2013/08/06/sunburn-pain-relief_n_3711613.html
The actual scientific study on which the above article was based is published in a very highly respected journal, Proceedings of the National Academy of Sciences:
http://www.pnas.org/content/110/34/E3225.long
The actual science here is impeccable. The research reports that a molecule, TRPV4, is involved in producing the pain of sunburn, and that a newly designed compound targeting this molecule inhibited the pain and blistering of sunburn in a mouse model. The implication is that such a compound could eventually be used to attenuate the burning and blistering of sunburn in humans.
Well, maybe.
The development of sunburn pain, like any pain, is a very complex cascade; this study shows that TRPV4 is an important part of that cascade. This is exciting new information, which has implications beyond sunburn. However, there are other well-known components of this cascade, including something called the "prostaglandin pathway." We already know how to inhibit prostaglandin-mediated pain and inflammation: the use of "non steroidal antiinflammatory drugs" (NSAIDS), of which ibuprofen is perhaps best known. It has been known for a long time that taking ibuprofen or similar agents right after excessive sun exposure markedly reduces pain and blistering.
The issue is that the pain and blistering of sunburn is really only a small part of the problem. The UV light which produces the sunburn also damages DNA in cells of the skin. This damage can ultimately lead to the development of skin cancers such as melanoma. As I have pointed out in other writings, melanoma caused by sunburn is the most common cause of death in outdoor recreation. Ibuprofen, or some expensive new TRPV4 antagonist, may well minimize the acute pain of sunburn. It would do nothing to prevent skin cancer. Sunburn is our body's way of saying "You jerk! Don't you know that you are setting yourself up for cancer?" Why would we want to do anything to take away from this important message?
http://www.huffingtonpost.co.uk/2013/08/06/sunburn-pain-relief_n_3711613.html
The actual scientific study on which the above article was based is published in a very highly respected journal, Proceedings of the National Academy of Sciences:
http://www.pnas.org/content/110/34/E3225.long
The actual science here is impeccable. The research reports that a molecule, TRPV4, is involved in producing the pain of sunburn, and that a newly designed compound targeting this molecule inhibited the pain and blistering of sunburn in a mouse model. The implication is that such a compound could eventually be used to attenuate the burning and blistering of sunburn in humans.
Well, maybe.
The development of sunburn pain, like any pain, is a very complex cascade; this study shows that TRPV4 is an important part of that cascade. This is exciting new information, which has implications beyond sunburn. However, there are other well-known components of this cascade, including something called the "prostaglandin pathway." We already know how to inhibit prostaglandin-mediated pain and inflammation: the use of "non steroidal antiinflammatory drugs" (NSAIDS), of which ibuprofen is perhaps best known. It has been known for a long time that taking ibuprofen or similar agents right after excessive sun exposure markedly reduces pain and blistering.
The issue is that the pain and blistering of sunburn is really only a small part of the problem. The UV light which produces the sunburn also damages DNA in cells of the skin. This damage can ultimately lead to the development of skin cancers such as melanoma. As I have pointed out in other writings, melanoma caused by sunburn is the most common cause of death in outdoor recreation. Ibuprofen, or some expensive new TRPV4 antagonist, may well minimize the acute pain of sunburn. It would do nothing to prevent skin cancer. Sunburn is our body's way of saying "You jerk! Don't you know that you are setting yourself up for cancer?" Why would we want to do anything to take away from this important message?
Wednesday, June 19, 2013
Updates and shameless promotion
Despite best of intentions for more regular posts, it's been a pretty dry few months!
Several recent Adirondoc columns are now available through the publications link.
Some time ago, I mentioned Erik Schlimmer's development of a route across the Adirondacks, from Blue Line to Blue Line, which he dubbed the "Trans Adirondack Route." Erik has now produced a guidebook and video for the route, both of which I highly recommend: http://www.transadk.com/
I was recently interviewed for a program ("Health Link") discussing the health benefits of wilderness travel. The link to the interview is: http://blogs.upstate.edu/healthlinkonair/2013/03/28/how-to-prepare-for-hiking-and-mountain-climbing/
Several recent Adirondoc columns are now available through the publications link.
Some time ago, I mentioned Erik Schlimmer's development of a route across the Adirondacks, from Blue Line to Blue Line, which he dubbed the "Trans Adirondack Route." Erik has now produced a guidebook and video for the route, both of which I highly recommend: http://www.transadk.com/
I was recently interviewed for a program ("Health Link") discussing the health benefits of wilderness travel. The link to the interview is: http://blogs.upstate.edu/healthlinkonair/2013/03/28/how-to-prepare-for-hiking-and-mountain-climbing/
Monday, December 31, 2012
Happy New Year!
Looking back over my posts for this year, I realize that I haven't been a very prolific blogger. Frankly, I can't understand how some folks have the time to keep their blogs so current! I have, however, continued to keep up my regular column for Adirondac magazine, most of which reads like a blog anyway. Check out the publication link for some of these.
With winter coming on, the Caribbean cruise industry is in full swing. I suspect that most readers of this blog don't spend too much time on vessels like the Queen Mary II, but there is actually a very nice wilderness medicine connection.
December was a bad month for cruise ships. In addition to rather flagrant violation of basic Leave No Trace principles (http://www.foe.org/cruise-report-card), there have been a number of very high profile outbreaks of intestinal infection on some luxury liners:
http://news.sky.com/story/1031527/norovirus-cruise-outbreaks-on-two-ships
How would you like to spend 10 grand or more for a cruise, and wind up puking on the floor of your cabin with the staff forbidden to enter your room? These are hardly isolated incidents; the Centers for Disease Control and Prevention has a nice summary of reports over the decade:
http://www.cdc.gov/nceh/vsp/surv/gilist.htm
Most of these outbreaks in which the cause could be established were related to Norovirus, a well-described cause of epidemic gastroenteritis. In addition, however, virtually every other infectious cause of gastroenteritis (including giardiasis) appears on this list.
Where's the backcountry connection? Believe it or not, there are actually some biologic similarities between cruise ships and backcountry treks. Both situations take a group of individuals from different backgrounds and locales and put them together for a prolonged period sharing close spaces, eating together, and sharing toileting facilities.
Epidemiologists have long recognized that such environments are a prime condition for the hand-to-mouth spread of intestinal infections. Poor hygiene on the part of cruisers leads to surfaces on the ship becoming contaminated, spreading infection. While this certainly can happen in other public venues such as restaurants and hotels, these do not keep the same group of people in the same environment for several days at a time. Cruise ships do not spend a lot of time worrying about their drinking water; instead, they are compulsive about cleaning surfaces and encouraging their clients to pay attention to personal hygiene. When outbreaks do occur, the CDC invariably implicates hand-to-mouth spread.
Except in developing countries with no sanitation infrastructure, water is not a very efficient means of spreading intestinal infections. As the cruise ship experience demonstrates, however, breakdown in personal sanitation is the major way in which such infections spread.
So, whether your winter travels will be in the Caribbean on a cruise or in the Wind River Range on a trek, enjoy and stay healthy. In either place, be sure to wash your hands!
With winter coming on, the Caribbean cruise industry is in full swing. I suspect that most readers of this blog don't spend too much time on vessels like the Queen Mary II, but there is actually a very nice wilderness medicine connection.
December was a bad month for cruise ships. In addition to rather flagrant violation of basic Leave No Trace principles (http://www.foe.org/cruise-report-card), there have been a number of very high profile outbreaks of intestinal infection on some luxury liners:
http://news.sky.com/story/1031527/norovirus-cruise-outbreaks-on-two-ships
How would you like to spend 10 grand or more for a cruise, and wind up puking on the floor of your cabin with the staff forbidden to enter your room? These are hardly isolated incidents; the Centers for Disease Control and Prevention has a nice summary of reports over the decade:
http://www.cdc.gov/nceh/vsp/surv/gilist.htm
Most of these outbreaks in which the cause could be established were related to Norovirus, a well-described cause of epidemic gastroenteritis. In addition, however, virtually every other infectious cause of gastroenteritis (including giardiasis) appears on this list.
Where's the backcountry connection? Believe it or not, there are actually some biologic similarities between cruise ships and backcountry treks. Both situations take a group of individuals from different backgrounds and locales and put them together for a prolonged period sharing close spaces, eating together, and sharing toileting facilities.
Epidemiologists have long recognized that such environments are a prime condition for the hand-to-mouth spread of intestinal infections. Poor hygiene on the part of cruisers leads to surfaces on the ship becoming contaminated, spreading infection. While this certainly can happen in other public venues such as restaurants and hotels, these do not keep the same group of people in the same environment for several days at a time. Cruise ships do not spend a lot of time worrying about their drinking water; instead, they are compulsive about cleaning surfaces and encouraging their clients to pay attention to personal hygiene. When outbreaks do occur, the CDC invariably implicates hand-to-mouth spread.
Except in developing countries with no sanitation infrastructure, water is not a very efficient means of spreading intestinal infections. As the cruise ship experience demonstrates, however, breakdown in personal sanitation is the major way in which such infections spread.
So, whether your winter travels will be in the Caribbean on a cruise or in the Wind River Range on a trek, enjoy and stay healthy. In either place, be sure to wash your hands!
Tuesday, August 7, 2012
"Sports Drinks" and the backcountry
The estimable British Medical Journal has just published a provocative expose on the "sports drink" industry. You know the stuff: Powerade, Gatorade, etc. As you're watching the Olympics, no doubt you've caught some screen shots of competitors drinking them and have seen their ads.
The theory behind these products is deceptively simple: Dehydration leads to decreased athletic performance. Salts are lost along with water during exercise. Exercise requires caloric expenditure. Voila! Along come products with a perfect balance of water, salt, and carbohydrate. The products come with an impressive resume of "clinical trials" attesting to their benefit, and are endorsed by a number of athletic organizations.
At first, I wasn't sure that this expose would be of interest to the wilderness traveller. As a little experiment, however, I checked out "sports drinks" and "electrolyte drinks" on a few of my favorite on-line retailers of backpacking gear: Campmor, EMS, and REI. All offer a wide variety of powdered and tablet forms of these for the camper. EMS, for example, features "GU Electrolyte Brew". The EMS website claims that the product will "get your system back in balance" and "help you go longer". Hum...
I urge you to read this report yourself. It is in the July 18, 2012 issue of the BMJ, which should be available in many university libraries. Online access is available at:
http://www.bmj.com/content/345/bmj.e4737.pdf%2Bhtml
The quick summary of the report is not pretty. The real science behind these drinks is almost completely lacking. Company claims to the contrary, when the medical journal attempted to review these studies it found virtually none of sufficient methodologic rigor to withstand scrutiny. The few which had been published in journals were overwhelmingly published in very low-impact journals with clear ties to the sports drink industry. For example, the journal Medicine and Science in Sports and Exercise is published by an organization with long-standing financial relationships to Gatorade, and has a number of "Gatorade affiliated scientists" on its editorial board.
The promoters of these products have largely "invented" dehydration as a common problem in endurance exercise, and have encouraged the promulgation of completely unsubstantiated recommendations for overhydration during sports. Unfortunately, these are filtering down to youth sports.
Is there a problem with all this? There is.
First of all, sports drinks contain calories--hundreds per serving. This may not be a problem for truly active folks, but the average person drinking Gatorade isn't Usein Bolt! By marketing an image of health and vigorous exercise, companies fool the average (mostly sedentary) user into thinking that he is drinking something other than, essentially, sugar water with a dash of salt.
More importantly, however, the widespread emphasis on sports hydration over the past few years is likely fueling a real problem: hyponatremia. This condition, which is basically a fancy name for water intoxication, is a serious cause of death and disability in some endurance sports. There are at least 16 recorded deaths and over a thousand critical illnesses in marathon running alone attributable to hyponatremia. Although sports drink makers insist that the salt content of their beverages avoids this complication, this is not correct. Indeed, an actual scientific study of marathon runners has shown that the volume of liquid consumed, independent of its composition, is the major factor in causing hyponatremia.
Millions of years of evolution have led to our bodies having an excellent mechanism for preventing dehydration. The mechanism is "thirst". Pay attention to it. When it calls, have a drink. Of water. Right from the stream!
The theory behind these products is deceptively simple: Dehydration leads to decreased athletic performance. Salts are lost along with water during exercise. Exercise requires caloric expenditure. Voila! Along come products with a perfect balance of water, salt, and carbohydrate. The products come with an impressive resume of "clinical trials" attesting to their benefit, and are endorsed by a number of athletic organizations.
At first, I wasn't sure that this expose would be of interest to the wilderness traveller. As a little experiment, however, I checked out "sports drinks" and "electrolyte drinks" on a few of my favorite on-line retailers of backpacking gear: Campmor, EMS, and REI. All offer a wide variety of powdered and tablet forms of these for the camper. EMS, for example, features "GU Electrolyte Brew". The EMS website claims that the product will "get your system back in balance" and "help you go longer". Hum...
I urge you to read this report yourself. It is in the July 18, 2012 issue of the BMJ, which should be available in many university libraries. Online access is available at:
http://www.bmj.com/content/345/bmj.e4737.pdf%2Bhtml
The quick summary of the report is not pretty. The real science behind these drinks is almost completely lacking. Company claims to the contrary, when the medical journal attempted to review these studies it found virtually none of sufficient methodologic rigor to withstand scrutiny. The few which had been published in journals were overwhelmingly published in very low-impact journals with clear ties to the sports drink industry. For example, the journal Medicine and Science in Sports and Exercise is published by an organization with long-standing financial relationships to Gatorade, and has a number of "Gatorade affiliated scientists" on its editorial board.
The promoters of these products have largely "invented" dehydration as a common problem in endurance exercise, and have encouraged the promulgation of completely unsubstantiated recommendations for overhydration during sports. Unfortunately, these are filtering down to youth sports.
Is there a problem with all this? There is.
First of all, sports drinks contain calories--hundreds per serving. This may not be a problem for truly active folks, but the average person drinking Gatorade isn't Usein Bolt! By marketing an image of health and vigorous exercise, companies fool the average (mostly sedentary) user into thinking that he is drinking something other than, essentially, sugar water with a dash of salt.
More importantly, however, the widespread emphasis on sports hydration over the past few years is likely fueling a real problem: hyponatremia. This condition, which is basically a fancy name for water intoxication, is a serious cause of death and disability in some endurance sports. There are at least 16 recorded deaths and over a thousand critical illnesses in marathon running alone attributable to hyponatremia. Although sports drink makers insist that the salt content of their beverages avoids this complication, this is not correct. Indeed, an actual scientific study of marathon runners has shown that the volume of liquid consumed, independent of its composition, is the major factor in causing hyponatremia.
Millions of years of evolution have led to our bodies having an excellent mechanism for preventing dehydration. The mechanism is "thirst". Pay attention to it. When it calls, have a drink. Of water. Right from the stream!
Wednesday, May 23, 2012
Just when I thought I'd heard everything....
The things folks do in the backcountry never cease to amaze me. Check out this recent item from the Albany Times Union regarding some guys who became lost recently in the Adirondacks:
http://m.timesunion.com/tu/db_109215/contentdetail.htm?contentguid=QCPcA8PG&full=true#display
Peeing on each other to stay warm? Yikees!
Of course, equally important to keeping warm is keeping dry. This was obviously a counterproductive strategy. Since their names were used in the article, I suspect that most of their friends have come across this news item. At least they survived.
This brings to mind an occasional question about hypothermia--is it better to hold onto urine because it is warm, or empty your bladder? (Urinating on another camper is not usually one of the choices.) The correct answer is that it makes no meaningful difference. Urine is only warm because the body keeps it heated, so in theory less heat would expended if there were less urine in the bladder to heat. In the big scheme of things, however, the impact of this on total heat balance would be trivial. More importantly, most people with serious hypothermia are somewhat dehydrated, so the most important thing is to be drinking enough that it isn't possible to hold it!
Just don't pee on your friends.
http://m.timesunion.com/tu/db_109215/contentdetail.htm?contentguid=QCPcA8PG&full=true#display
Peeing on each other to stay warm? Yikees!
Of course, equally important to keeping warm is keeping dry. This was obviously a counterproductive strategy. Since their names were used in the article, I suspect that most of their friends have come across this news item. At least they survived.
This brings to mind an occasional question about hypothermia--is it better to hold onto urine because it is warm, or empty your bladder? (Urinating on another camper is not usually one of the choices.) The correct answer is that it makes no meaningful difference. Urine is only warm because the body keeps it heated, so in theory less heat would expended if there were less urine in the bladder to heat. In the big scheme of things, however, the impact of this on total heat balance would be trivial. More importantly, most people with serious hypothermia are somewhat dehydrated, so the most important thing is to be drinking enough that it isn't possible to hold it!
Just don't pee on your friends.
Monday, April 9, 2012
The "Trans Adirondack" Route
Erik Schlimmer is a good friend with whom I have guided in Alaska previously. He is one of the few people who approach me in the volume of untreated Adirondack water he has consumed without ill effects!
Erik has a number of "firsts" under his wilderness belt, most of which I would have no desire to duplicate. (Canoeing the lower Hudson? Yuck!) His most recent, however, looks like a lot of fun. He has outlined a 235 mile route which traverses the Adirondack Park. He will be releasing a guidebook early next year (Blue Line to Blue Line) which details the route.
This summer, Erik is working with one of his former students to produce a documentary which will coincide with the launch of his book. Information on the route and the planned documentary is available at:
http://www.kickstarter.com/projects/1559964226/trans-adirondack-route-documentary
Erik has a number of "firsts" under his wilderness belt, most of which I would have no desire to duplicate. (Canoeing the lower Hudson? Yuck!) His most recent, however, looks like a lot of fun. He has outlined a 235 mile route which traverses the Adirondack Park. He will be releasing a guidebook early next year (Blue Line to Blue Line) which details the route.
This summer, Erik is working with one of his former students to produce a documentary which will coincide with the launch of his book. Information on the route and the planned documentary is available at:
http://www.kickstarter.com/projects/1559964226/trans-adirondack-route-documentary
Saturday, March 17, 2012
Survival Lesson
For many of our frontcountry friends, outdoor education somehow equates with survival training. Such staples of television as "Man vs Wild" and "Survivorman" certainly add to this view. I had a personal taste of this a while ago when interviewed for a newspaper profile (http://adirondoc.com/publications/profile_post_061209.pdf). Not being a fan of the Discovery Channel (We only pay for basic cable.), I had a difficult time believing the reporter's questions about the utility of eating bugs and drinking urine as a survival skill. Apparently, such tripe is regular fare on such programs.
I was thinking about this the other day while reading about the seemingly amazing story of a 41 year old woman surviving a 3 1/2 week "ordeal" in the mountains of New Mexico (http://www.columbiatribune.com/news/2012/mar/10/missing-woman-survives-weeks-lost-in-nm-forest/).
No food--no water purification devices--no map or compass--below-freezing nights--her destination unknown to friends or family: this seemed like an obvious set up for fatality.
How did she survive?
Although the data are sketchy, it seems that she pretty much ignored common teaching about survival in such situations.
First of all, she drank plenty of water from a nearby creek, without fretting about its quality. While this might seem pretty basic, compare it to the arguably better-prepared chap I discussed in an earlier posting (April 27, 2010), who nearly died after a shorter period being lost because he avoided drinking for fear of water-borne illness.
Then, there is the matter of food. We often hear that the body cannot survive longer than ten days without food. This has led to the nonsense of courses on "edible plants", trapping small animals, eating bugs, etc. No one seems to realize that the energy expended by such efforts likely exceeds the minimal caloric content of the "food". Actually, the body's tolerance of extended fasting is well documented--time in excess of 40 days has been shown for centuries. Indeed, mammalian physiology is well adapted for extended periods without eating. (This is the reason that calorie restriction alone is rarely sufficient for extended weight loss.) The woman in question wasted no time or energy in pursuit of food.
She also stayed put. Although conventional teaching might have called for her to follow the nearby creek downstream, she chose not to do so. (Apparently, the unfortunate woman had some emotional disorder which contributed to her predicament, so this may not have been an informed "choice".) Rather than wasting energy and risking injury by walking distances, she simply stayed put, stayed warm, stayed dry, and waited. There are not too many areas in the US where a lost person cannot ultimately be found if she waits long enough--especially after abandoning a car.
Sure, she made some mistakes (albeit possibly intentional) which led to her near-miss. Nonetheless, we should remember the lesson of Margaret Page before pontificating on wilderness survival to our students.
I was thinking about this the other day while reading about the seemingly amazing story of a 41 year old woman surviving a 3 1/2 week "ordeal" in the mountains of New Mexico (http://www.columbiatribune.com/news/2012/mar/10/missing-woman-survives-weeks-lost-in-nm-forest/).
No food--no water purification devices--no map or compass--below-freezing nights--her destination unknown to friends or family: this seemed like an obvious set up for fatality.
How did she survive?
Although the data are sketchy, it seems that she pretty much ignored common teaching about survival in such situations.
First of all, she drank plenty of water from a nearby creek, without fretting about its quality. While this might seem pretty basic, compare it to the arguably better-prepared chap I discussed in an earlier posting (April 27, 2010), who nearly died after a shorter period being lost because he avoided drinking for fear of water-borne illness.
Then, there is the matter of food. We often hear that the body cannot survive longer than ten days without food. This has led to the nonsense of courses on "edible plants", trapping small animals, eating bugs, etc. No one seems to realize that the energy expended by such efforts likely exceeds the minimal caloric content of the "food". Actually, the body's tolerance of extended fasting is well documented--time in excess of 40 days has been shown for centuries. Indeed, mammalian physiology is well adapted for extended periods without eating. (This is the reason that calorie restriction alone is rarely sufficient for extended weight loss.) The woman in question wasted no time or energy in pursuit of food.
She also stayed put. Although conventional teaching might have called for her to follow the nearby creek downstream, she chose not to do so. (Apparently, the unfortunate woman had some emotional disorder which contributed to her predicament, so this may not have been an informed "choice".) Rather than wasting energy and risking injury by walking distances, she simply stayed put, stayed warm, stayed dry, and waited. There are not too many areas in the US where a lost person cannot ultimately be found if she waits long enough--especially after abandoning a car.
Sure, she made some mistakes (albeit possibly intentional) which led to her near-miss. Nonetheless, we should remember the lesson of Margaret Page before pontificating on wilderness survival to our students.
Monday, February 20, 2012
Northeast Wilderness Medicine Conference
Upstate New York will be hosting a major national conference on wilderness medicine from May 31, 2012 through June 2, 2012. A number of WM experts will be on hand, and the broad program offers something for everyone. Additional information and online registration are available at: http://upstate.edu/emergency/outreach/conferences/newm/index.php
Hope to see you there!
Hope to see you there!
Thursday, December 1, 2011
Wheezing in the Wilderness
Asthma is a big problem in the United States, and one which is growing annually. Somewhere between 3000 and 4000 people die from the disease in this country annually; this figure includes about 200 to 300 children. While I am unaware of confirmed asthma deaths in the setting of backcountry treks, the disease is so common it is inevitable that some folks with asthma will have difficulty in the wilderness.
Most specialists in asthma believe that the bulk of these deaths are unnecessary. Many of them result not from the lack of appropriate therapy but from failure to use well-established therapies in the appropriate fashion and time.
There is a major national initiative ongoing to improve all of this. One big component of it is the development of personal "asthma action plans" (AAPs). These are documents which are developed for individual patients with their physicians, which provide specific directions for treatment depending upon actual symptoms. There are several versions of AAPs, but all are predicated on the individual's assessment of his or her condition as "green" (good), "yellow" (not good), or "red" (awful). The plan provides specific medication suggestions for each zone. Here's a link to a nice example of an AAP:
http://cpnonline.org/CRS/CRS/pa_actionpl_art.htm
How does this relate to the wilderness? Although this system has become state-of-the-art for asthma care in the US, it has largely not penetrated first aid courses--any courses, not just wilderness ones. I recently reviewed over a dozen wilderness first aid textbooks and none even mentioned the AAP. Instead, they had a variety of generic recommendations regarding inhalers, perhaps enhanced by some attempt at explaining esoteric lung physiology, none of which were particularly useful. I guess that I shouldn't find this too surprising, since at a panel discussion in which I took part a while ago the representative of a major provider of wilderness first aid training commented that he had asthma himself and never heard of an asthma action plan!
Is there an "action item" for the wilderness educator here? You bet there is. Part of the pre-trek process in most programs is some sort of medical history/screening/release. I firmly believe that if any prospective participants provide a history of asthma, they must have an up to date personal AAP, a copy of which accompanies them on the expedition. Of course, there is also a need to be sure that the individual has an adequate supply of any or all drugs called for in the AAP.
What if someone does not have this? Although I hardly ever criticize fellow physicians (I know you'll find that hard to believe!), this is a time when it is appropriate to do so. Simply put, a physician caring for a patient with asthma in the 21st century who does not provide an asthma action plan is providing substandard care. This isn't just me--the Center for Medicare and Medicaid Services (CMS) has a standard for hospitals that patients with asthma must be provided with AAPs upon discharge. Failure to do so can actually result in hospital sanctions.
Therefore, I believe that programs have an obligation to their participants to notify them that they must discuss with their physician the development of an AAP and must bring one along with them.
Most specialists in asthma believe that the bulk of these deaths are unnecessary. Many of them result not from the lack of appropriate therapy but from failure to use well-established therapies in the appropriate fashion and time.
There is a major national initiative ongoing to improve all of this. One big component of it is the development of personal "asthma action plans" (AAPs). These are documents which are developed for individual patients with their physicians, which provide specific directions for treatment depending upon actual symptoms. There are several versions of AAPs, but all are predicated on the individual's assessment of his or her condition as "green" (good), "yellow" (not good), or "red" (awful). The plan provides specific medication suggestions for each zone. Here's a link to a nice example of an AAP:
http://cpnonline.org/CRS/CRS/pa_actionpl_art.htm
How does this relate to the wilderness? Although this system has become state-of-the-art for asthma care in the US, it has largely not penetrated first aid courses--any courses, not just wilderness ones. I recently reviewed over a dozen wilderness first aid textbooks and none even mentioned the AAP. Instead, they had a variety of generic recommendations regarding inhalers, perhaps enhanced by some attempt at explaining esoteric lung physiology, none of which were particularly useful. I guess that I shouldn't find this too surprising, since at a panel discussion in which I took part a while ago the representative of a major provider of wilderness first aid training commented that he had asthma himself and never heard of an asthma action plan!
Is there an "action item" for the wilderness educator here? You bet there is. Part of the pre-trek process in most programs is some sort of medical history/screening/release. I firmly believe that if any prospective participants provide a history of asthma, they must have an up to date personal AAP, a copy of which accompanies them on the expedition. Of course, there is also a need to be sure that the individual has an adequate supply of any or all drugs called for in the AAP.
What if someone does not have this? Although I hardly ever criticize fellow physicians (I know you'll find that hard to believe!), this is a time when it is appropriate to do so. Simply put, a physician caring for a patient with asthma in the 21st century who does not provide an asthma action plan is providing substandard care. This isn't just me--the Center for Medicare and Medicaid Services (CMS) has a standard for hospitals that patients with asthma must be provided with AAPs upon discharge. Failure to do so can actually result in hospital sanctions.
Therefore, I believe that programs have an obligation to their participants to notify them that they must discuss with their physician the development of an AAP and must bring one along with them.
Wednesday, October 5, 2011
What do ticks, heart attacks, and protozoa have in common?
I recently did a column in my wilderness health series in Adirondac magazine on the topic of ticks (http://adirondoc.com/publications/ticked_off_072011.pdf). I warned the editor that as soon as the column came out, he would be receiving irate letters. He didn't believe me.
The ink on the magazine was hardly dry when the first complaint came across his desk.
I was taken severely to task for minimizing the problem of Lyme disease among users of the outdoors.
Read the piece and judge for yourself. Lyme disease is a nasty affliction, but virtually always treatable with a short course of a common antibiotic; deaths from Lyme in the US are virtually unheard of. "Chronic" Lyme disease exists mainly in the minds of a group of unfortunate folks with some sort of chronic pain syndrome and a group of "specialists" who make a living from them. Hikers in tick-infested areas should take some simple precautions, but not consume much mental energy worrying about them.
The whole thing got me thinking about the irrational way in which those of us in the outdoor education industry decide what to worry about. It isn't just ticks.
I spend a lot of time working with challenge course programs, especially around issues of "medical screening". There have been a few (actually very few) cases of sudden cardiac death involving users of these courses, although on a per-participant-hour basis the actual risk is statistically at baseline (http://adirondoc.com/publications/sudden_death_2002.pdf). (Remember, over 300,000 people experience sudden cardiac death annually, and every one of them was doing something at the time!) This has not stopped some in the industry from arguing for exhaustive (and completely unvalidated) screening methods to select out those at risk. This has reached the ludicrous point of some arguing that failure to implement such screening is "unethical"! Of course, experienced cardiologists will tell you that they cannot predict the risk of sudden death in any specific individual, but this has not stopped facilitators from implementing simplistic checklists--preventing nothing but also potentially depriving folks who could benefit from such a program from participating.
I have commented previously on the silliness which has inflicted many outdoor instructors regarding the risk of water-borne giardiasis. Although the scientific data on this problem are abundantly clear, there continue to be programs which enforce water treatment strategies which are entirely unsupported by data. Some of these are so bizarre (keeping utensils which are "dipped" in suspect water separate from "clean" ones; flushing out the microliters of water caught in screw-top water bottle grooves) they seem more suited for the Book of Leviticus than outdoor education materials.
The problem with this sort of thing is that there actually are some very good data which should inform our decision making in these areas. Sadly, most outdoor education programs do not seem to integrate such epidemiologic data into their policy development.
We worry needlessly about water quality, while rarely enforcing hand sanitation--a far better way to address the spread of intestinal infection on the trail. We push for wide availability of "Epi Pens" without prescription to trek leaders, with virtually no data pointing to anaphylaxis as an actual problem in outdoor education courses. Of course, those who push for Epi Pens are not the ones advocating flu shots and immunization updates--a vastly more important intervention for a group about to set out on a lengthy expedition. Many programs insist on lengthy "woofer" courses and refreshers for their leaders, in the face of absolutely no evidence that such programs meaningfully impact safety, even if a fraction of their skills could be retained. Epidemiologic data clearly point to automobile accidents and drowning as the major causes of death on treks--have you ever heard of a program with a mandatory driver education or water safety recertification requirement?
In my "day job" as an academic physician, I am constantly surrounded by the drumbeats of those insisting that everything we do be firmly grounded in evidence. When I step into the outdoor education arena, however, it appears that unsubstantiated opinion, anecdote, and dogma regularly trump evidence.
We must do better.
The ink on the magazine was hardly dry when the first complaint came across his desk.
I was taken severely to task for minimizing the problem of Lyme disease among users of the outdoors.
Read the piece and judge for yourself. Lyme disease is a nasty affliction, but virtually always treatable with a short course of a common antibiotic; deaths from Lyme in the US are virtually unheard of. "Chronic" Lyme disease exists mainly in the minds of a group of unfortunate folks with some sort of chronic pain syndrome and a group of "specialists" who make a living from them. Hikers in tick-infested areas should take some simple precautions, but not consume much mental energy worrying about them.
The whole thing got me thinking about the irrational way in which those of us in the outdoor education industry decide what to worry about. It isn't just ticks.
I spend a lot of time working with challenge course programs, especially around issues of "medical screening". There have been a few (actually very few) cases of sudden cardiac death involving users of these courses, although on a per-participant-hour basis the actual risk is statistically at baseline (http://adirondoc.com/publications/sudden_death_2002.pdf). (Remember, over 300,000 people experience sudden cardiac death annually, and every one of them was doing something at the time!) This has not stopped some in the industry from arguing for exhaustive (and completely unvalidated) screening methods to select out those at risk. This has reached the ludicrous point of some arguing that failure to implement such screening is "unethical"! Of course, experienced cardiologists will tell you that they cannot predict the risk of sudden death in any specific individual, but this has not stopped facilitators from implementing simplistic checklists--preventing nothing but also potentially depriving folks who could benefit from such a program from participating.
I have commented previously on the silliness which has inflicted many outdoor instructors regarding the risk of water-borne giardiasis. Although the scientific data on this problem are abundantly clear, there continue to be programs which enforce water treatment strategies which are entirely unsupported by data. Some of these are so bizarre (keeping utensils which are "dipped" in suspect water separate from "clean" ones; flushing out the microliters of water caught in screw-top water bottle grooves) they seem more suited for the Book of Leviticus than outdoor education materials.
The problem with this sort of thing is that there actually are some very good data which should inform our decision making in these areas. Sadly, most outdoor education programs do not seem to integrate such epidemiologic data into their policy development.
We worry needlessly about water quality, while rarely enforcing hand sanitation--a far better way to address the spread of intestinal infection on the trail. We push for wide availability of "Epi Pens" without prescription to trek leaders, with virtually no data pointing to anaphylaxis as an actual problem in outdoor education courses. Of course, those who push for Epi Pens are not the ones advocating flu shots and immunization updates--a vastly more important intervention for a group about to set out on a lengthy expedition. Many programs insist on lengthy "woofer" courses and refreshers for their leaders, in the face of absolutely no evidence that such programs meaningfully impact safety, even if a fraction of their skills could be retained. Epidemiologic data clearly point to automobile accidents and drowning as the major causes of death on treks--have you ever heard of a program with a mandatory driver education or water safety recertification requirement?
In my "day job" as an academic physician, I am constantly surrounded by the drumbeats of those insisting that everything we do be firmly grounded in evidence. When I step into the outdoor education arena, however, it appears that unsubstantiated opinion, anecdote, and dogma regularly trump evidence.
We must do better.
Saturday, July 30, 2011
A "game changer" in grizzly territory?
You may have heard about the recent grizzly attack involving a group of NOLS students in Alaska's Talkeetna Mountains. A good rendition of the story is in this article from the Alaska Dispatch:
http://www.alaskadispatch.com/article/alaska-bear-attack-nols-kids-did-phenomenal-job
The story hit home, as this is a part of Alaska in which I have led scores of students during WEA courses over the past decade. The story is of particular interest to those of us who take groups into grizzly country, as it appears to be the first example of an exception to a rule we all hold as gospel: grizzlies do not attack large groups. Is this a "game changer" for outdoor educators?
Although the mantra appears in various forms, it is best stated by David Smith in his estimable book Backcountry Bear Basics. Smith reports that there has never been an injury to a group of six or more, nor a fatality in a group of four or more. He believes that this is because such a group is more likely to be noisy, to be seen early by the bear, and to give the bear pause before initiating a charge.
As best I can tell, this statement has never been challenged by anyone knowledgeable. The Alaska Department of Fish and Game apparently believes it. I discussed this the other day with Bill Porter, a friend who is a senior wildlife biologist at Michigan State University, who also concurs.
So, what happened? Obviously, we will probably never know for sure, but from the report in the paper I have a theory. Although the group size was sufficient to be protective, I have to wonder about how close together they were. Apparently, they were walking in a creek--a particularly dangerous place in the Talkeetnas in late July--when they came upon the sow and her cub. I suspect that the group was spread out somewhat, and that the mother thought she was being challenged by a single individual. She attacked, and it was only after that that the rest of the group wandered into the location.
Fortunately, the student had the knowledge and wits to do exactly the right thing: play dead. This worked, as the bear then left him for another student. Obviously, the vaunted NOLS bear procedure training saved the boy's life.
So, what is the lesson here for the outdoor leader in grizzly territory? I believe that we can continue to say with integrity that there is safety in numbers. What we must reinforce to our students, however, is that only applies if the group is tightly together--close enough to be seen as one. This is easier said than done--groups tend to spread out, and many resent being told to keep together. This incident, however, reminds us that this must always be the practice in bear country.
http://www.alaskadispatch.com/article/alaska-bear-attack-nols-kids-did-phenomenal-job
The story hit home, as this is a part of Alaska in which I have led scores of students during WEA courses over the past decade. The story is of particular interest to those of us who take groups into grizzly country, as it appears to be the first example of an exception to a rule we all hold as gospel: grizzlies do not attack large groups. Is this a "game changer" for outdoor educators?
Although the mantra appears in various forms, it is best stated by David Smith in his estimable book Backcountry Bear Basics. Smith reports that there has never been an injury to a group of six or more, nor a fatality in a group of four or more. He believes that this is because such a group is more likely to be noisy, to be seen early by the bear, and to give the bear pause before initiating a charge.
As best I can tell, this statement has never been challenged by anyone knowledgeable. The Alaska Department of Fish and Game apparently believes it. I discussed this the other day with Bill Porter, a friend who is a senior wildlife biologist at Michigan State University, who also concurs.
So, what happened? Obviously, we will probably never know for sure, but from the report in the paper I have a theory. Although the group size was sufficient to be protective, I have to wonder about how close together they were. Apparently, they were walking in a creek--a particularly dangerous place in the Talkeetnas in late July--when they came upon the sow and her cub. I suspect that the group was spread out somewhat, and that the mother thought she was being challenged by a single individual. She attacked, and it was only after that that the rest of the group wandered into the location.
Fortunately, the student had the knowledge and wits to do exactly the right thing: play dead. This worked, as the bear then left him for another student. Obviously, the vaunted NOLS bear procedure training saved the boy's life.
So, what is the lesson here for the outdoor leader in grizzly territory? I believe that we can continue to say with integrity that there is safety in numbers. What we must reinforce to our students, however, is that only applies if the group is tightly together--close enough to be seen as one. This is easier said than done--groups tend to spread out, and many resent being told to keep together. This incident, however, reminds us that this must always be the practice in bear country.
Tuesday, June 28, 2011
Hand sanitizers work!
As is often the case, the best new wilderness medicine news is not in the outdoor or the wilderness medicine literature. Instead, it can be found in rigorous studies reported in major peer-reviewed journals. A recent study reported in the Pediatric Infectious Disease Journal is a case in point.
With the recognition that poor personal hygiene, not drinking water, is the real culprit leading to gastrointestinal distress among backpackers, more attention is being paid to hand sanitation. Although good ol' soap and water is the tried and true approach to this, it is not always practical in the backcountry. Lately, a lot of folks have been using alcohol-based hand sanitizers instead. Although I have admired their attention to hygiene, I have wondered if this approach was effective.
A group of French investigators have studied the hand sanitizer intervention in a group with a huge susceptability to hand-to-mouth transmission of gastroenteritis: 5 to 10 year old kids. Basically, the intervention was quite simple. In one school, all students underwent supervised use of hand sanitizers several times a day. In another school, they did not. The numbers of children developing diarrhea and/or vomiting during the study period were compared between the schools. The "intervention" school experienced about half of the number of GI infections as the control school. There were similar differences demonstrated between the schools in doctor visits, days lost from school, and working days lost by parents. There were no complications associated with the use of the gel.
Other studies have looked at the biology of this (effectiveness of gels in killing organisms in the lab) and at the use of the agents in the health care setting. This is the first well-designed trial of such an intervention among laypersons. The results are pretty impressive.
Sure, a French elementary school ain't a trek in the wilderness. Yet, the impressive results in a very high-risk group with very large numbers is compelling. I think that we can rest assured that this approach in the back country is now evidence-based.
The exact citation for the study is: Pediatric Infectious Disease Journal 2010;29(11)994-998.
With the recognition that poor personal hygiene, not drinking water, is the real culprit leading to gastrointestinal distress among backpackers, more attention is being paid to hand sanitation. Although good ol' soap and water is the tried and true approach to this, it is not always practical in the backcountry. Lately, a lot of folks have been using alcohol-based hand sanitizers instead. Although I have admired their attention to hygiene, I have wondered if this approach was effective.
A group of French investigators have studied the hand sanitizer intervention in a group with a huge susceptability to hand-to-mouth transmission of gastroenteritis: 5 to 10 year old kids. Basically, the intervention was quite simple. In one school, all students underwent supervised use of hand sanitizers several times a day. In another school, they did not. The numbers of children developing diarrhea and/or vomiting during the study period were compared between the schools. The "intervention" school experienced about half of the number of GI infections as the control school. There were similar differences demonstrated between the schools in doctor visits, days lost from school, and working days lost by parents. There were no complications associated with the use of the gel.
Other studies have looked at the biology of this (effectiveness of gels in killing organisms in the lab) and at the use of the agents in the health care setting. This is the first well-designed trial of such an intervention among laypersons. The results are pretty impressive.
Sure, a French elementary school ain't a trek in the wilderness. Yet, the impressive results in a very high-risk group with very large numbers is compelling. I think that we can rest assured that this approach in the back country is now evidence-based.
The exact citation for the study is: Pediatric Infectious Disease Journal 2010;29(11)994-998.
Tuesday, March 29, 2011
What happens in the wilderness, redux
One concern I have long had about the wilderness first responder "movement" has been the disconnect between their content and the actual data speaking to the types of medical events encountered in typical backcountry expeditions. When I discuss this with folks (as at a recent AORE conference), a frequent refrain is that there are not enough good data about such events.
Bull %*#*.
In actuality, there are a number of registries and large series which have been the basis for numerous publications in the peer-reviewed medical literature over the past few decades. Indeed, the database from NOLS has produced three such publications. The fascinating thing about all of these reports is that they are strikingly consistent. In fact, it could be argued that we have had enough such studies.
Now along comes yet another such report, this time from the esteemed outdoor education program at Cornell University ("COE"). Although there is very little in the way of surprises here, this is a particularly well done study which did just about everything right. Ironically, the study is accompanied by an editorial which perfectly illustrates the fact that some folks just don't care about data.
First, the study itself. COE is a large program with an excellent ability to record, capture, and analyze data from its many treks. This report covered a six-year period, with 74,005 participant days. The activities included the usual suspects in such college programs, although there was an inordinate emphasis on climbing walls (nearly two thirds of the participant days). The remainder were more typical: backpacking, mountaineering, natural (rock and ice) surface climbing, various water sports, etc. Overall, the injury/illness rate in this large series was 1.5/1000 participant days. This is extremely close to the rate reported in previous studies from NOLS and Outward Bound. About one-third of these events necessitated evacuation, again a figure consistent with other reports. The distribution of these events was also very similar to a host of similar previous publications. Most (over half) were skin and soft-tissue injuries. There were no deaths, serious injuries, or (see one of my previous blog commentaries) anaphylaxis. There were ten fractures/dislocations, of which three were ankle and one was tib-fib. The other fractures were seemingly trivial: wrist, collarbone, nose and coccycx. The latter ("tailbone") is an injury many of us active folks have probably had without realizing it because of not taking an xray; I rarely if ever radiate someone's pelvis to document this fracture.
In a very thoughtful discussion, the authors of this report comment on the safety culture at COE, as well as their use of such data to inform programing. For example, the number of injuries associated with food preparation (lacerations and burns) has led to some changes in instruction. The authors assert, very correctly, that the pattern and severity of injuries in their outdoor recreation are dwarfed by those of other college sports. All in all, a very nice study. The publication information is: Wilderness and Environmental Medicine; 2010; 21:363-370. You can download a pdf from the journal's website.
The editors of the journal should have left well enough alone. They didn't. When the editors of a medical journal believe that there is something worthy of highlighting in an issue, they occasionally solicit an "editorial" to emphasize the study's importance. Inexplicably, the editors chose a WFR instructor with no apparent background or qualification in epidemiology to editorialize on the study. The editorial was generally lame and ill-informed. For example, the author considered it "surprising" to learn that outdoor recreation injury rates were lower than intercollegiate sports, although this observation has been widely known for decades, first publicized by Project Adventure in their safety studies. More troublesome, the editorialist violated a major rule of an editorial by using it to include unreviewed new data. He somehow turned the discussion around to femur fractures, using a alleged incident from one of his former students to "report" the successful construction of an ad hoc traction splint on a mountaineering trek. He went on to advocate for the teaching of and utilization of this technique.
This is a completely unsubstantiated case report, which has now made its way into the medical literature without peer review--a travesty for a medical journal. Femur traction splints constructed out of sticks, trekking poles, and similar items have been a staple of WFR courses for a long time. When I mention such constructions to trauma surgery colleagues, I generally get a "you've got to be kidding" response. My favorite description of the technique is from the Outward Bound First Aid Handbook: "Improvised traction splints employing ski poles, canoe paddles, and other pieces of equipment are more often architecturally interesting than medically useful." Amen. WFR course time spent on such nonsense teaches students techniques they will probably forget, will never need, and wouldn't work anyway.
Kudos to COE for a very helpful report. Darts to Wilderness and Environmental Medicine for spoiling it with a silly editorial.
Bull %*#*.
In actuality, there are a number of registries and large series which have been the basis for numerous publications in the peer-reviewed medical literature over the past few decades. Indeed, the database from NOLS has produced three such publications. The fascinating thing about all of these reports is that they are strikingly consistent. In fact, it could be argued that we have had enough such studies.
Now along comes yet another such report, this time from the esteemed outdoor education program at Cornell University ("COE"). Although there is very little in the way of surprises here, this is a particularly well done study which did just about everything right. Ironically, the study is accompanied by an editorial which perfectly illustrates the fact that some folks just don't care about data.
First, the study itself. COE is a large program with an excellent ability to record, capture, and analyze data from its many treks. This report covered a six-year period, with 74,005 participant days. The activities included the usual suspects in such college programs, although there was an inordinate emphasis on climbing walls (nearly two thirds of the participant days). The remainder were more typical: backpacking, mountaineering, natural (rock and ice) surface climbing, various water sports, etc. Overall, the injury/illness rate in this large series was 1.5/1000 participant days. This is extremely close to the rate reported in previous studies from NOLS and Outward Bound. About one-third of these events necessitated evacuation, again a figure consistent with other reports. The distribution of these events was also very similar to a host of similar previous publications. Most (over half) were skin and soft-tissue injuries. There were no deaths, serious injuries, or (see one of my previous blog commentaries) anaphylaxis. There were ten fractures/dislocations, of which three were ankle and one was tib-fib. The other fractures were seemingly trivial: wrist, collarbone, nose and coccycx. The latter ("tailbone") is an injury many of us active folks have probably had without realizing it because of not taking an xray; I rarely if ever radiate someone's pelvis to document this fracture.
In a very thoughtful discussion, the authors of this report comment on the safety culture at COE, as well as their use of such data to inform programing. For example, the number of injuries associated with food preparation (lacerations and burns) has led to some changes in instruction. The authors assert, very correctly, that the pattern and severity of injuries in their outdoor recreation are dwarfed by those of other college sports. All in all, a very nice study. The publication information is: Wilderness and Environmental Medicine; 2010; 21:363-370. You can download a pdf from the journal's website.
The editors of the journal should have left well enough alone. They didn't. When the editors of a medical journal believe that there is something worthy of highlighting in an issue, they occasionally solicit an "editorial" to emphasize the study's importance. Inexplicably, the editors chose a WFR instructor with no apparent background or qualification in epidemiology to editorialize on the study. The editorial was generally lame and ill-informed. For example, the author considered it "surprising" to learn that outdoor recreation injury rates were lower than intercollegiate sports, although this observation has been widely known for decades, first publicized by Project Adventure in their safety studies. More troublesome, the editorialist violated a major rule of an editorial by using it to include unreviewed new data. He somehow turned the discussion around to femur fractures, using a alleged incident from one of his former students to "report" the successful construction of an ad hoc traction splint on a mountaineering trek. He went on to advocate for the teaching of and utilization of this technique.
This is a completely unsubstantiated case report, which has now made its way into the medical literature without peer review--a travesty for a medical journal. Femur traction splints constructed out of sticks, trekking poles, and similar items have been a staple of WFR courses for a long time. When I mention such constructions to trauma surgery colleagues, I generally get a "you've got to be kidding" response. My favorite description of the technique is from the Outward Bound First Aid Handbook: "Improvised traction splints employing ski poles, canoe paddles, and other pieces of equipment are more often architecturally interesting than medically useful." Amen. WFR course time spent on such nonsense teaches students techniques they will probably forget, will never need, and wouldn't work anyway.
Kudos to COE for a very helpful report. Darts to Wilderness and Environmental Medicine for spoiling it with a silly editorial.
Saturday, February 26, 2011
Column Resumes
For several years, I wrote a regular column for the magazine of the Adirondack Mountain Club, Adirondac. They were having some financial challenges which caused their page allotment to shrink, so the column has been on hiatus.
The editor has asked me to resume the column in the summer, and I am doing so. As in the past, it will provide advice on the health and safety aspects of outdoor recreation, targeting a lay audience. The initial column will discuss some aspects of canoe safety. The Adirondack Mountain Club does not as yet have an online version of the magazine, but I will post the columns in the Publication area of my website.
The editor has asked me to resume the column in the summer, and I am doing so. As in the past, it will provide advice on the health and safety aspects of outdoor recreation, targeting a lay audience. The initial column will discuss some aspects of canoe safety. The Adirondack Mountain Club does not as yet have an online version of the magazine, but I will post the columns in the Publication area of my website.
Thursday, January 6, 2011
Best Giardia Story Ever
A buddy of mine who works as a college outdoor education instructor recently shared an experience with me. For reasons I will mention later, today is an amazingly appropriate day to bring this up.
My friend related a visit to one of the college's treks by a student instructor from the west. The visitor was appalled to learn that this particular program did not practice universal water treatment during their expeditions. When told that the local instructors had carefully considered things and no longer recommended routine treatment of most Adirondack waters, he commented that it must be because of something unique to New York, since tasting even a drop of untreated water in the American west was "guaranteed" to result in giardiasis. He went on with a litany of reasons why this was to be avoided at all costs, not the least being that giardiasis was essentially incurable, and that those unfortunate enough to acquire it would have it forever--often flaring up any time an offending food was consumed. He treated everything he drank on the trek. No one else did. Everyone was just fine.
Of course, everything about this would be simply silly if it were not for the fact that the person involved is en route to becoming a professional outdoor educator, presumably about to share such nonsense with unsuspecting students. This is hardly a "controversy" anymore; it is difficult to identify any true expert in this field who considers the "treat everything" approach to be necessary or appropriate. Which brings me to the reason why today is a very good time to tell this tale.
A report today (http://www.nytimes.com/aponline/2011/01/05/health/AP-EU-MED-Autism-Fraud.html?_r=2&ref=health) has confirmed once and for all that the original study linking vaccines to autism was not only incorrect, it was fraudulent. The 1998 study, by a British quack named Andrew Wakefield, reported 12 reportedly normal children in whom autism developed as a consequence of the MMR vaccine. The journal in which it was published retracted it long ago because of concerns about its validity, and all of Wakefield's coauthors disassociated themselves with its conclusions. Literally scores of well-designed studies involving thousands of children have been published subsequently, none of which have supported the Wakefield hypothesis. One would think that the concern would have gone away by now.
Sadly, things didn't work out that way. In the nearly 13 years since the Wakefield publication, concern about the MMR vaccine became rampant, leading many families to avoid it. This, in turn, has resulted in a resurgence of measles in the world, with countless preventable deaths. Nonetheless, uninformed "experts" have continued to trump this bogus association, believing a study of 12 patients over well-designed trials with thousands.
Believe it or not, this situation is nearly identical to the current infatuation of some wilderness folks with water-borne giardiasis.
There has been exactly one peer-reviewed scientific study suggesting a link between wilderness water consumption and giardiasis. This report, from 1976, reported that about 2/3 of participants in a camping trip in Utah's Uinta mountains acquired giardiasis. The authors ascribed the outbreak to consumption of surface water.
In subsequent years, it has become clear this this report was incorrect (although certainly not fraudulent--just wrong). Analyzing this incident in light of contemporary knowledge about giardiasis has made it clear that this was an epidemic of food- or hand-to-mouth borne infection. (This is discussed in more detail in a paper available on my website: http://adirondoc.com/publications/water_quality_2004.pdf).
Although no subsequent scientific studies have shown any association between North American wilderness water consumption and giardiasis (or, indeed, any infection), the damage was done with the single 1976 paper, just as it was with Wakefield's 1998 autism/vaccine study. "True believers" such as the student instructor continue to tout misinformation which has been long-since discredited--often embellishing it along the way.
While the damage done by this over 30 year old paper pales in comparison to that of the Wakefield study (I doubt that anyone has died because of it!), it certainly has had negative effects. Most strikingly, the incessant attention to water quality in the backcountry has eclipsed attention to a much more important strategy--hand washing---which probably would have prevented the Utah outbreak! It has created the market for a dizzying array of technologic fixes (filters, "steri-pens", etc) which exist to solve a problem which doesn't exist. It has perpetuated very bad science among folks who aspire to professional careers in outdoor education.
I'll conclude with a "stay tuned". With a couple of colleagues and a student, I am analyzing data from a series of studies we have done examining the colonization of backpackers' hands with (hope you're not eating lunch now) organisms found in FECES. Without giving away the results, let me just suggest that you avoid shaking hands with folks you meet in the wilderness...
My friend related a visit to one of the college's treks by a student instructor from the west. The visitor was appalled to learn that this particular program did not practice universal water treatment during their expeditions. When told that the local instructors had carefully considered things and no longer recommended routine treatment of most Adirondack waters, he commented that it must be because of something unique to New York, since tasting even a drop of untreated water in the American west was "guaranteed" to result in giardiasis. He went on with a litany of reasons why this was to be avoided at all costs, not the least being that giardiasis was essentially incurable, and that those unfortunate enough to acquire it would have it forever--often flaring up any time an offending food was consumed. He treated everything he drank on the trek. No one else did. Everyone was just fine.
Of course, everything about this would be simply silly if it were not for the fact that the person involved is en route to becoming a professional outdoor educator, presumably about to share such nonsense with unsuspecting students. This is hardly a "controversy" anymore; it is difficult to identify any true expert in this field who considers the "treat everything" approach to be necessary or appropriate. Which brings me to the reason why today is a very good time to tell this tale.
A report today (http://www.nytimes.com/aponline/2011/01/05/health/AP-EU-MED-Autism-Fraud.html?_r=2&ref=health) has confirmed once and for all that the original study linking vaccines to autism was not only incorrect, it was fraudulent. The 1998 study, by a British quack named Andrew Wakefield, reported 12 reportedly normal children in whom autism developed as a consequence of the MMR vaccine. The journal in which it was published retracted it long ago because of concerns about its validity, and all of Wakefield's coauthors disassociated themselves with its conclusions. Literally scores of well-designed studies involving thousands of children have been published subsequently, none of which have supported the Wakefield hypothesis. One would think that the concern would have gone away by now.
Sadly, things didn't work out that way. In the nearly 13 years since the Wakefield publication, concern about the MMR vaccine became rampant, leading many families to avoid it. This, in turn, has resulted in a resurgence of measles in the world, with countless preventable deaths. Nonetheless, uninformed "experts" have continued to trump this bogus association, believing a study of 12 patients over well-designed trials with thousands.
Believe it or not, this situation is nearly identical to the current infatuation of some wilderness folks with water-borne giardiasis.
There has been exactly one peer-reviewed scientific study suggesting a link between wilderness water consumption and giardiasis. This report, from 1976, reported that about 2/3 of participants in a camping trip in Utah's Uinta mountains acquired giardiasis. The authors ascribed the outbreak to consumption of surface water.
In subsequent years, it has become clear this this report was incorrect (although certainly not fraudulent--just wrong). Analyzing this incident in light of contemporary knowledge about giardiasis has made it clear that this was an epidemic of food- or hand-to-mouth borne infection. (This is discussed in more detail in a paper available on my website: http://adirondoc.com/publications/water_quality_2004.pdf).
Although no subsequent scientific studies have shown any association between North American wilderness water consumption and giardiasis (or, indeed, any infection), the damage was done with the single 1976 paper, just as it was with Wakefield's 1998 autism/vaccine study. "True believers" such as the student instructor continue to tout misinformation which has been long-since discredited--often embellishing it along the way.
While the damage done by this over 30 year old paper pales in comparison to that of the Wakefield study (I doubt that anyone has died because of it!), it certainly has had negative effects. Most strikingly, the incessant attention to water quality in the backcountry has eclipsed attention to a much more important strategy--hand washing---which probably would have prevented the Utah outbreak! It has created the market for a dizzying array of technologic fixes (filters, "steri-pens", etc) which exist to solve a problem which doesn't exist. It has perpetuated very bad science among folks who aspire to professional careers in outdoor education.
I'll conclude with a "stay tuned". With a couple of colleagues and a student, I am analyzing data from a series of studies we have done examining the colonization of backpackers' hands with (hope you're not eating lunch now) organisms found in FECES. Without giving away the results, let me just suggest that you avoid shaking hands with folks you meet in the wilderness...
Thursday, December 2, 2010
Why mosquitos love us and hate DEET
It's hard to be thinking about mosquitos during the first lake effect event of the season, but maybe it will get you into the mood for summer!
For a long time, I have endorsed the usual understanding of the mechanism by which mosquitos target warm-blooded animals. For quite a while, it has been recognized that there is a complex neurochemical mechanism by which the bugs are attracted to carbon dioxide. From an evolutionary standpoint, this makes a lot of sense: if you are looking for a blood meal, what better way to find it than by going after something which breathes out carbon dioxide? It is also consistent with our backcountry observations. How many times, for example, have you noticed the propensity of these creatures to congregate under the tent fly?
This understanding has also permitted me to pooh-pooh students in my classes who claim that something about their own sweat, soap, or BO is particularly attractive to mosquitos. I have generally dismissed them as whiners, and pontificated that there was no biologic mechanism for such an observation. How could a bug distinguish between Dr. Bronner's and Mountain Suds?
Mea culpa.
Complex modern science has now shown us that the smell detection system of mosquitos is vastly more complicated than we ever could have imagined. In the process, it has also uncovered the biologic explanation for the effectiveness of DEET. Pretty impressive.
The study (by Liu and associates at Vanderbilt) is available online from the journal PLoS Biology (http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000467). The molecular biology here is daunting, and not for the faint of heart. Also keep in mind that the work was done with an African mosquito; it is certainly plausible, however, that similar mechanisms are in place for other species.
These scientists have unraveled the existence of two distinct olfactory signaling pathways in these insects. Each of these pathways (AgOR and AgIR) consists of a family of specific receptors, each of which, presumably, can respond to specific odors. Such responses can be either attractive or repulsive. A specific receptor (AgOR7) appears to be the actual target of DEET; animals in whom this receptor was inactivated by microinjection of specific RNA fragments were no longer affected by DEET.
What can we take away from this elegant science? Carbon dioxide is still a potent attractant for mosquitos, but short of stopping breathing there is nothing we can do about it. DEET works--we know this from a lot of previous behavioral studies, and now we understand it at the molecular level. From a wealth of other studies, we also know that the health concerns of DEET are vastly overblown and can generally be ignored. Mosquitos also seem to be capable of responding to a lot of other olfactory stimuli, but we do not as yet understand what makes something attractive or repulsive.
Bottom line--it is now plausible that certain individuals are more attractive to mosquitos than others. Other than DEET and protective garmets, however, there is little to do other than sucking it up!
For a long time, I have endorsed the usual understanding of the mechanism by which mosquitos target warm-blooded animals. For quite a while, it has been recognized that there is a complex neurochemical mechanism by which the bugs are attracted to carbon dioxide. From an evolutionary standpoint, this makes a lot of sense: if you are looking for a blood meal, what better way to find it than by going after something which breathes out carbon dioxide? It is also consistent with our backcountry observations. How many times, for example, have you noticed the propensity of these creatures to congregate under the tent fly?
This understanding has also permitted me to pooh-pooh students in my classes who claim that something about their own sweat, soap, or BO is particularly attractive to mosquitos. I have generally dismissed them as whiners, and pontificated that there was no biologic mechanism for such an observation. How could a bug distinguish between Dr. Bronner's and Mountain Suds?
Mea culpa.
Complex modern science has now shown us that the smell detection system of mosquitos is vastly more complicated than we ever could have imagined. In the process, it has also uncovered the biologic explanation for the effectiveness of DEET. Pretty impressive.
The study (by Liu and associates at Vanderbilt) is available online from the journal PLoS Biology (http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000467). The molecular biology here is daunting, and not for the faint of heart. Also keep in mind that the work was done with an African mosquito; it is certainly plausible, however, that similar mechanisms are in place for other species.
These scientists have unraveled the existence of two distinct olfactory signaling pathways in these insects. Each of these pathways (AgOR and AgIR) consists of a family of specific receptors, each of which, presumably, can respond to specific odors. Such responses can be either attractive or repulsive. A specific receptor (AgOR7) appears to be the actual target of DEET; animals in whom this receptor was inactivated by microinjection of specific RNA fragments were no longer affected by DEET.
What can we take away from this elegant science? Carbon dioxide is still a potent attractant for mosquitos, but short of stopping breathing there is nothing we can do about it. DEET works--we know this from a lot of previous behavioral studies, and now we understand it at the molecular level. From a wealth of other studies, we also know that the health concerns of DEET are vastly overblown and can generally be ignored. Mosquitos also seem to be capable of responding to a lot of other olfactory stimuli, but we do not as yet understand what makes something attractive or repulsive.
Bottom line--it is now plausible that certain individuals are more attractive to mosquitos than others. Other than DEET and protective garmets, however, there is little to do other than sucking it up!
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