Category Archives: infectious disease

SteriPEN, convenient or worthless?

Clean water is of utmost importance, whether you’re backcountry hiking, camping, or travelling abroad. And there are many ways to disinfect water, including chemical tablets, mechanical filters, simply boiling, and ultraviolet light. And while we know that UV light from the sun works with enough contact time, does a handheld UV light work well enough to be safe?

They’ve been around since the late 90s, but decreases in size and cost have made them more popular recently. They are lighter than ceramic filters, don’t require heating and then cooling the water, and they don’t leave a funky taste in the water after use. And while you can go to SteriPENs’s website and see a bunch of articles they sponsored showing how awesome they are, it’s nice that an independent group has finally looked into their effectiveness.

One of the things the article points out is that UV light is bacteriostatic, not bacteriocidal. Their DNA is damaged, so they can’t reproduce or cause infection (probably), but the water is disinfected, not sterile. Also, while still effectively treated by UV light, viruses and spores require much higher doses to be inactivated.

They tested the function against of the SteriPEN against water bottles contaminated with Escherichia coli, Staphylococcus aureus, and the spore of Geobacillus stearothermophilus. Using 1 L bottles in 3 different styles (wide mouth reusable, narrow mouth reusable, and disposable narrow mouth bottles), they either agitated as per the instructions for the device, or let the water remain calm. For wide mouth containers, you can stir. With narrow mouth bottles, you need to plug the mouth with the pen and invert and shake. However, knowing that many people don’t do this, they also did a test by simply stirring the narrow mouth bottle as well. They also measured the spectrum emitted by the device during use.

Used correctly the SteriPEN works pretty well. Bacteria counts were reduced more than 99.99%, but spores were only reduced 99.57% on average. If you don’t agitate the water, this drops to 94.2% on average. The SteriPEN does emit its maximal intensity of UV at 254nm, which is the most efficient wavelength for bacterial DNA. And in a bottle made of glass, PET, or metal, there’s no risk of UV injury to the user, as it’s all blocked. However, in a big open-topped pot, there’s a risk of UV emission that could be hazardous to the eyes. Thankfully, the device won’t turn on if not immersed in water.

Therefore it is ok to use a SteriPEN to disinfect your water, as long as you’re doing it right. You’ve got to agitate the water, not just put it in and let it sit there. These authors also didn’t test against viruses, but the manufacturer does have data, and since this paper replicates some of their other results, it’s not unreasonable to state that it likely works against those as well.

Downsides are a few. 4 AA batteries only gives you 100 cycles and the bulb is pretty fragile, so pack extras. It doesn’t filter out toxins, and turbid water decreases efficacy, so you might night a filter anyway. This particular device has 2 settings, 90s of light for 1L containers, 48s for 0.5L ones, so you’ll need to make sure you have it set for the correct size as well. Finally, it doesn’t keep the water disinfected forever, so be aware that the water can become contaminated again and require re-treatment.

Drinking water treatment with ultraviolet light for travelers – Evaluation of a mobile lightweight system
And it’s FOAMed!

Komodo dragons: Myth vs Reality

The Komodo dragon is a creature that inspires fear and mysticism in many. It’s got all the characteristics of a good monster movie: only found on rare tropical islands, large, and possessing magical saliva that can kill. First identified by the west in 1910 by Dutch sailors, they reported the lizards could spit fire and reached 7m in length. In reality the lizard can only get up to 3m and can weigh 70kg, and none have been identified as either breathing or spitting fire.

Komodo dragon (Varanus komodoensis), Komodo National Park, Indonesia

This review comes after a zoo worker was bitten on the hand by a small Komodo dragon. She had transient hypotension, and a retained tooth on xray. This was not removed, and after loose approximation (Ed. note: never do this), she was discharged on antibiotics. Thankfully the tooth came out on its own, and she did not develop a deep space infection. After this case report, the authors decided to do a literature review, knowing that it would help them get published.

Many of us are taught in school that Komodo dragon saliva is a possibly venomous, potentially fatal concoction of particularly virulent bacteria, including E. Coli, Staphylococcus, Streptococcus, and Pasteurella. These bacteria live in the rotting flesh that they leave in their mouth. But what is that based on?

It turns out, not much. The “facts” we have in textbooks, zoos, and medical literature are based on one guy’s book written in 1981. While Walter Auffenberg was the Jane Goodall of Komodo dragons, moving to the island and studying them in their natural habitat, his results haven’t been widely reproducible. And, more importantly, komodos don’t carry rotting flesh in their mouth. They fastidiously clean their teeth and gums. Now, perhaps the water buffalo does die of sepsis after being bitten, but if it does, it’s because it runs into murky water with fresh wounds, and not from bacteria in the mouth of the lizard. So, the “bacteria as venom” concept is just as dead in the water as the buffaloes.

So what about the venom aspect? The author of that study (Fry) was able to identify glands in the lower jaw that could potentially be venom glands. Furthermore, the extract of those glands does in fact contain proteins that inhibit blood clotting similar to snake venom. However, there isn’t any evidence that the venom actually affects the prey or is secreted in any significant amount during bites. The teeth lack venom grooves present in every other venomous animal (including the shrew). On the plus side, the author did come up with the “grip, rip, and drip” model of lethality from komodos.

Then why do animals die after being bitten by a large, reptilian predator? For the same reasons they die after being bitten by any large animal. Direct trauma, blood loss, and hypovolemic shock (and by eating).

Our findings are also in accord with the view that the killing technique of V. komodoensis is broadly similar to that of some sharks and Smilodon fatalis (saber cat). Despite obvious anatomical differences, these unrelated predators kill or are thought to have killed (respectively) large prey by using relatively weak bite forces amplified by sharp teeth and postcranial input.

They have strong neck muscles and serrated teeth, so after they bite they pull away, tearing holes in the prey that then bleeds to death. Is it possible that venom can increase this bleeding? Sure, but it’s also possible that it doesn’t.

So then why did this patient become hypotensive? Likely a vasovagal response. And given that the bite was on the hand, it’s appropriate to put the patient on antibiotics. But maybe we can finally stop propagating the magical thinking associated with komodo dragons.

Bitten by a Dragon

Further enjoyable reading
National Geographic
A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus

Want to repel mosquitoes?

Mosquitoes. Mozzies. Whatever name you want to use for them, they’re a nuisance to you when you’re outdoors. And even worse, if you are in certain areas, they can transmit a large number of serious diseases. So which repellent is best? While I covered botanical mosquito repellents previously, this review article examines the products most of us think of when someone mentions mozzie spray.

At 38 pages, this is no light read. It’s certainly more words on mosquitoes than I’ve ever read in one sitting. But it’s full of interesting information, both trivial and applicable. For instance, did you know that the US Army had the patent on DEET for a full 11 years before they allowed civilian use?

As detailed in the article, not only are there several species of mosquitoes, there are also several formulations of repellent, and even seemingly minor things such as local weather patterns that can affect how long any particular product will work. Something as simple as wearing dark clothing can attract biters as they are able to see you better. Carbon dioxide, lactic acid, carboxylic acids, and even sweat will also attract mosquitoes, as their olfactory receptors are keen on these smells.

Using specific search strings, the authors found 1417(!)articles between 2000 and 2012, and they further pared this down to 102 when they only included repellent efficacy on human skin. The main repellents studied were DEET, Insect Repellent 3535, Icaridin (Picaridin), and Citriodora. DEET, being the gold standard, is often what others are compared against.

So what should you use?

  • DEET 20-25%
  • IR3535 10-20%
  • Icaridin 10-20%
  • Citriodora 20-30% (cream)

If you want to repel mosquitoes, a high concentration DEET product (20-25%) has the greatest repellency against all species, and conveniently it lasts the longest. It is clearly the most effective at repelling Aedes spp. Of note, in their data, they found that going over 25% DEET doesn’t offer greater protection against Aedes spp., but it does have longer repellency against Anopheles spp. Of note, it also has the most side effects, up to and including neuro- and cardiotoxicity.

IR3535 at concentrations of 10-20% works against most mosquitoes, but puzzlingly loses some efficacy against Anopheles at higher concentrations. Icaridin is also effective at 10-20%. Using IR3535 or Icaridin is reasonable, especially if you want to wear anything that DEET can destroy, such as rayon, spandex, vinyl, plastic, or even leather. 

Citriodora (lemon scented eucalyptus extract) is useful when applied as a cream, but is ineffective when used as just the essential oil. Speaking of essential oils and other “natural repellents”, these authors actually looked at a fair amount of studies, and found that some really are effective. These include catmint oil and rosemary, among others. And to really mess with you, adding 5% vanillin to anything, synthetic or natural, makes it more effective. However, most are fairly volatile and short-lived. Sorry I couldn’t give you more ammo against certain Facebook users.

The authors also included tick (Ixodes) repellent efficacy in this article, but found the data wanting. DEET, IR3535, and Icaridin all seem effective, but it isn’t conclusive.

The efficacy of repellents against Aedes, Anopheles, Culex and Ixodes spp.-A literature review

How you wash your utensils matters

When you’re out in the wild for extended periods of time, you’re always reminded of the need to eat. Some get around this by only carrying pre-prepared foods. Others decide to cook, which inevitably leads to dirty dishes. Even if you make the grave sin of using disposable dishes and silverware, you still have to clean the larger containers you prepare the food in. And when somewhere between 1/3 and 3/4 of hikers end up with diarrhea, cleaning of these dishes is clearly important. 

If you’re car camping and have running water, you can go ahead and move on to another blog post. Fresh running potable water makes this job easy. But for those times when it isn’t available, you need to clean your utensils somehow. Many of us have been taught the 3 bowl system seen above, where you wash in the first bowl, rinse in the second, and disinfect in the third. It has similarities to the 3 sink systems many restaurants use. But does this mean it’s best?

To find out, a group of authors decided to test 18(!) different 3 bowl systems to see which actually reduced bacterial loads the most. They used porridge contaminated with E. coli, a practice I can’t recommend when camping. (They describe the contamination in excruciating detail, using 232 words). The authors trimmed the systems to 10 after finding 8 of them “wholly inadequate.” Describing each of the systems is needlessly complex, so here’s Table 1 from the article. Table 1

This doesn’t entirely explain their methods though. When they wrote “established”, they meant washing until visibly clean in first bowl, then using 2 and 3 just for rinsing and sanitizing, as it were. “Alternative” meant removing all easy food residue in bowl 1, then getting them visibly clean in bowl 2, and rinsing in bowl 3.

Their results weren’t entirely surprising. First they note that grease is only removed with detergent. Second, while systems D, F, G, and J were best for bacterial loads, E through I were easiest to use because you could see what you were washing easier in the cleaner bowl 2, and D-I where the ones that didn’t leave a disinfectant smell on the dishes when done. Putting this all together, the winner was system G in using the least bleach while still reducing coliform counts below measurable levels.

Of note, systems B and C are often what is used and taught for wilderness trips. This may be due to a real or perceived need to decontaminate the rinsing water, but the authors recommend using potable water for bowl 3. Otherwise you are left with a distinct disinfectant residue on your dishes that can be tasted at your next meal. More importantly, due to reduced contact time with the disinfectant (dunking takes less time than cleaning), they had higher coliform counts as well.

So there you have it. You can use the 3 bowl system, but not the way it’s been taught historically. You should have water and detergent in the first bowl, cleaning them mostly. Then continue cleaning until visibly clean in a second bowl of water with 10mL of bleach in it (5L:10mL water:bleach). Finally, rinse in potable water. In severely water restricted circumstances,  this system gives you the added benefit of still working when you remove the 3rd bowl, except for that disinfectant taste again. The authors do note that if an outbreak of diarrhea occurs at your campsite, consider increasing the bleach content of bowl 2 to 100mL.

Laboratory evaluation of the 3-bowl system used for washing-up eating utensils in the field.