Monthly Archives: September 2013

Drinking water on the cheap

Anyone who goes backpacking knows that suitable water can be hard to find.  Contaminated water can make for serious health problems. For those areas where people live with contaminated water, the problem is compounded, as children have significantly higher mortality from diarrheal illnesses.  Many of these places lack the resources to implement costly solutions to this problem.  This paper looks at a relatively inexpensive way to purify water. As a significant component of wilderness medicine is improvisation, it is applicable in survival situations as well.

The authors attempted to answer multiple questions.  The first was simply, can solar water disinfection (SODIS) work with the contaminated water from a large city in Pakistan? Second, are there ways to increase the efficiency of the SODIS system?  Third, to what effect does the intensity of the sunlight affect disnifection?  Fourth, how much plasticizer leaches into the water with heating?  Their materials were locally made PET bottles, natural sunlight, the rooftop of the building, and foil and black paint.

The untreated water had 827 CFU/100mL of total coliforms, with 82.3 CFU/100mL of fecal coliform.  With all 3 types of vessel (transparent, reflective with foil, and absorptive with black paint), 90% of total coliforms were inactivated within 4 hours.  The absorptive vessel had the highest temperature attained, and also had the most effectiveness for removing coliforms in strong sunlight, while the reflective worked best in weak and moderate sunlight.  They also determined that the amount of plasticizer present after heating was significantly lower than the WHO guideline value for safety.  Even if it weren’t, in a pinch, a single dose of DEHP is less toxic than known enteric pathogens.

This paper continues the trend of showing the efficacy of using passive solar disinfection to make safe drinking water.

Application of solar water disinfection for treatment of contaminated public water supply in a developing country: field observations.

Palm cooling, effective or not?

RTX cooling, or Rapid Thermal Exchange, started with two Stanford researchers in the 90s looking at rewarming patients after surgery.  The basis is that mammals have arteriovenous anastamoses in the palms and soles, and this can be used to bring high volumes of blood in contact with a thermal plate.  A small vacuum is created in the device to further increase blood flow.  The inventors received a DARPA grant to study the device for possible military use.  It came into vogue in the athletic and wilderness fields as an easy and effective way to decrease or increase core temperature.  A secondary benefit of increased endurance was noticed in some trials, and this is being looked at by a few.  Currently devices are in use by many sports teams, including the San Francisco 49ers.
The curious thing is, if you look through the 9 studies available on pubmed using palm cooling as the search, you’ll notice not all of them are positive.
The positive studies are authored by:

The negative studies are authored by:

Certainly sample size in all of these is low, and perhaps the device is effective at cooling and/or endurance increase.  However, based on the literature available, it is 5 in favor, 4 against.  Then consider that 2 of the 5 positive papers are written by the owners of the patent for the device (Grahn and Heller).  I would wait to purchase one of these devices for my personal gym.

Don’t be like Goldilocks

Bears are big and dangerous.  Certainly, they don’t typically go out looking for people, but people continue to go further into bear habitats, increasing the chances of injury.
This paper in the journal Injury describes bear attack patients who presented to a tertiary center in Kashmir and injury patterns they sustained.  They made sure to exclude injuries received from fleeing, and only those caused directly by bears. Importantly, the attacks were from the Asiatic black bear, which is known for its aggression.  All patients were alone when they were attacked, reportedly collecting firewood or reaping corncobs.  They do not comment if they were campers or simply villagers.  Rabies prophylaxis was given to all patients, the rationale was “none of them had been able to kill the attacking bear and hence the rabies status of the animal was unknown.”
They do comment on the attacks themselves, and the pertinent information included:

  • 28 of the attacks were in people trying to scare the bear away
  • 4 recalled a bear with cubs
  • Most attacks (26) occurred June-October (attributed to pre-hibernation foraging)
  • Significant transportation delays occurred, with only 2 patients presenting within 6 hours
The injury patterns described were varied, but included:
  • Majority upper extremity injuries
  • 18 open fractures of various grades
  • 1 lower extremity injury
  • 4 eye injuries
  • 2 mandibular fractures, and 2 skull fractures
  • Finger amputations and muscle avulsions were common
  • Head and neck injuries were from teeth, but arm injuries were from claws
  • Eleven patients developed infections of their wounds, all were mixed flora.
The authors close by recommending routine rabies and tetanus prophylaxis, and careful exploration of “even apparently minor wounds” as they can hide tendon, vessel, and bone injuries.  They recommend against closing cutaneous wounds secondary to infection risk. The only caveats to this study I can see are that there is likely sampling bias, as minor injuries either did not present to the tertiary center or were not identified by the authors.
Pattern of orthopaedic injuries in bear attacks: Report from a tertiary care centre in Kashmir

Which is the best botanical mosquito repellent?

Many people don’t like to use DEET-based mosquito repellents due to reports of toxicity, the fact that DEET can dissolve plastic, or just a desire to be more natural.  However, DEET is still the gold standard for insect repellents. So how would botanical mosquito repellents work compared to that? Unfortunately, the authors of this paper did not compare the botanicals to DEET, but did compare citronella, geraniol, and linalool to each other.

To do this they took 4 people (the authors themselves!) and used their exposed legs as a test patch for mosquito bites.  Then for 9 tests, they were exposed for 3 hours to indoor environments with mosquitoes using either candles or diffusers as their only defense.  The second leg of the experiment involved pasture next to a canal in Puerto Rico during the dry season, using a trap to collect mosquitoes in the middle of 4 mounted diffusers.

The results are interesting.  Indoors, all of the diffusers were better at repelling than control, but geraniol was better than the others.  Candles were not as effective as diffusers indoors, but the results were the same, with geraniol beating the others, and all being better than nothing.  Citronella had the least repellent effect for both.

Outdoor results were similar, except they didn’t test candles. Geraniol diffusers reduced mosquito counts by 95.5% over control. Linalool and citronella lagged behind again. Placing the diffusers closer to the trap resulted in better repelling.

The results show that those citronella candles available for purchase really aren’t useful for repelling mosquitoes. If you can source a geraniol diffuser (Fasst Products in the paper), you’ve got a pretty good botanical repellent though.

Efficacy of the botanical repellents geraniol, linalool, and citronella against mosquitoes.