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Backcountry Water Treatment, Part 4: Ultrafiltration
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- Опубліковано 21 бер 2022
- This video is Part 4 in a series on Backcountry Water Treatment methods, focusing on Ultrafiltration purifiers, also known as the removal of viruses (in addition to bacteria and cysts) from drinking water by size-exclusion.
It addresses the claim that viruses are too small to be filtered by hollow-fiber membranes with 0.02-micron ratings, looks at filter options available in this class, and discusses the viral risks in backcountry waters.
There are also sections on the health threat of flood waters in a disaster, and the tactic of filtering your water twice for the additional removal of pathogens.
Watch the entire Backcountry Water Treatment series here:
• Backcountry Water Trea...
Index
00:21 Is Virus Filtration a Myth?
16:22 Section Summary
17:00 Virus Filters
22:42 Viral Risk Factors
32:42 Filtering the Risk
35:23 Section Summary
36:27 Water Treatment During Disasters
38:15 Tactic of Filtering Twice
41:22 Runt Microbe Theory
43:02 Rogue Pore Theory
50:03 Conclusion
Don't worry about the time they take. We're all here for the quality of information and the thoughtful insight behind it.
Thanks! I appreciate that!
I second this :-)
I didn't even realize this was almost an hour long until I read your comment!
@@GearSkepticyour videos are awesome Thankyou. Best on UA-cam
I was a microbiology and chemistry major in college and then went to medical school and residency and taught at a program. I don't recall hearing any lectures nearly as well presented and complete as your programs. I'm totally blown away.
Thank you so much! That is very generous of you, and I sincerely appreciate it.
Watching your videos feels like I'm getting a whole college degree worth of information, and with no ads as well! Thank you so much for sharing your research
You’re very welcome! I hope it helps!
It's unreal that you don't have a million subscribers. Social media would tell me that about 11 out of 10 people "enjoy hiking". Excellent material, thank you!
Egad! How would I handle that many comments? 😜
You already are Harrison ford to me. The dedication of 10+ years is astounding!!!! You deserve awards for all your work and the fact that you simply want to make it better for everyone in this capitalistic society makes you a superhero. You deserve all of the backpacking community's attention.
Thank you! Very kind of you and I appreciate it.
Wow. You have done the outdoor enthusiast and the emergency preparedness folks a great service. After watching your videos on backpacking food and water treatments, I feel more confident in the choices I have for each. Thanks again and keep up the excellent work.
You are most welcome, and thanks very much!
@@GearSkeptic I just finished a 5 day hike in the Gila National Forest. On day 4 I didn't encounter a stream with water for several hours and by then I needed to resupply my potable H2O. I came across a nasty, foul looking, shallow stream in an area where livestock fed and watered. So, I first "filtered" the water through my hankerchief. Then I filtered that through a Sawyer filter. I then treated that water with my Aquamira Chlorine Dioxide A/B system. Lastly, I filtered the water again as a drank it. Whew! If I'd had my steripen I would have used that as well. I thought of this video the entire time, too. Thanks again!
Yikes! Sounds challenging, but I’m glad you were okay. Type 2 fun!
Your videos tickle my brain in the best possible way. Thank you for your above-and-beyond effort in these. Clear, concise, and realistic. Excellent work as usual.
Very kind of you! Thanks!
This series is "life's work" type quality.
Most kind of you. Much appreciated!
Everytime I think of a flaw in your logic, you later address it. Thank you for your work and presentation! I look forward to each video you post.
Thank you! I appreciate you saying so 😁
Thank you for these videos, the effort and time you put into them is apparent and appreciated.
With all this information and more on the way we'll need a part 7 with recommendations based on location, weight, risk tolerance etc.
Good point! Part 7 is going on the planner…
this feels like a school project where you're really trying to impress your teacher(us) and doing everything in your power to present it. It is great!
So neat how there's a UA-cam expert in every field imaginable, great videos!
I’ve binge watched all your videos over the last three days, and I look forward to your future videos. Thank you for all your research and your amazing contribution to the hiking and backpacking community!
Oh and if no one has told you yet, you have a pleasant voice.
Thanks very much! That is kind of you to say.
Small correction at 41:20, the Katadyn filter actually accepts water in via the looped ends that then flows out the tube ends (top of your diagram), basically the arrows are backwards. This allows more surface area of the smaller pores exposed to the dirty water that can then flow out the larger tube ends without trapping debris inside the tubes. Unless you're talking about something else and I misunderstood.
Great video series though, you really have a way of narrowing down what actually matters and going deep on it. Can't wait for the next one.
If anyone needs a paper topic I'd love to see the test results on multiple filtration passes.
New gear skeptic video??? My day is made.
It only takes you a day to absorb a single GearSkeptic video? What is your trick, as I have to go over and over them time and time again
I wish everyone could have the benefit of this knowledge. Thank you!
You are most welcome!
Honestly, don’t fret about the upload times brother. The information and perspective you share is invaluable!
Thanks! I appreciate that!
Thank you for putting in all the hard work. I think we all value the quality and do not want you to feel rushed in any way. The rushed feeling likely is the internet being excited about the very compelling hard work you are providing. Keep it up and stay safe! Cheers and have a great weekend!
Thanks very much! I will try to keep my eye on the ball 🙂
The amount of effort taken avoiding mentions of a certain issue preceding the creation of that video by 2 years is truly astonishing! Well played, sir!
Been binging on your videos, and all I have to say is WOW!
You talk about calorie density, but your videos are tops when it comes to useful information density per minute.🙂
After struggling with wats to further reduce pack weight, I’ve concluded it would have to come from food and water.
You’ve provided the data I need to achieve my goal. Keep up the great work.
Thanks! I appreciate that and am very glad if it can help!
As always thank-you for all the work you put into these!
As always, you are most welcome! 😉
Thank you for all the work you've done!
This channel is seriously underrated. Thank you for the effort
Thanks for the effort and time you put into these videos.
Dedication, pure dedication! And I love it.
Thanks very much!
Thank you. The time and effort you put into this must be epic. Thank you again.
I can’t describe the amount of joy I get from the thoroughness, thoughtfulness, and humor in each of these. Thank you :).
Thank you! That’s very kind of you to say, and I take it to heart!
This is lifesaving effort that I have long suspected to need be done. Even the US Military and EPA/CDC do not want to reveal the growing contamination in public water supplies due to severe weather and mechanical/chemical failure. It is expensive to test well water, so most people do not do this. Furthermore water sold over the counter or delivered to homes are only scantily tested for pathogens. The chemical contents and heavy metals in American water varies widely. Additionally how do they detect microplastics in public water? A recent article about 50% of fish caught in waters around Miami showed pharmaceuticals present in their flesh, according to the Miami Times last week. This is a very serious matter. Thank you for your analysis!
Made my day to see a new video from you. Thanks for all the hard work that goes into them.
Much appreciated! Thank you!
Thanks again for your quality content.
Ah yes, quality content. Will have to watch all of these again
Holy smokes that was an insane amount of research! Thank you so much for doing that for benefit of the community!
Another very informative video in this series. Thanks for the attention to detail & relentless pursuit of reference material in your research. I also love the quote "A mistake can travel halfway across the internet before the truth can put its boots on".
Thanks! And, that is also a favorite quote of mine 👍🏼
Great video, I just got in to backpacking so , I just found your channel . Thank you for all your hard work and great research . I think your " just the facts" and scientific out look is grate!! Just what i was looking for . Again ....Thank you for sharing
Thank you for all of your incredible videos!
You are most welcome!
Thank you for all your time, effort and work.
You are most welcome!
Appreciate the videos!! Take all the time you need to make the videos you can stand behind, it's worth the wait. Looking forward to videos 5 and 6.
Thanks!
What an amazing service you provide us all with!
Thanks much! I’m very glad if any of it can be useful.
I was just about to comment an ask about UV filtration like the steri pen. Super excited to see it. You are doing amazing high effort work going through tons of technical papers and crunching these numbers and even giving real world examples so it's not just an incomprehensible mess of numbers. Absolutely amazing work.
Thank you! That means a lot to me.
Thanks for another great video
Thank you for your time and effort with these awesome vids.
You are most welcome and thank you, too!
Bravo! Amazingly thorough video, thank you for doing the research!
Thanks! I appreciate that.
Thank you so much for all you do!
You’re most welcome! I hope it helps.
OH SHIT! HERE WE GO AGAIN! Thank you, yet again.
Another rabbit hole! 🤓
All I can say is wow!!! The time and research and editing is beyond the realm of time spent, per feedback and google pay. You my sir deserve to be highly recommended and accommodated for your efforts. Please keep up the great work you provide. Tip of the hat and a heartfelt thank you!!
Thank you! Very generous to say 😀
Love your videos- truly valuable and thorough.
Thank you!
got like 3 minutes into this video and SUBSCRIBED
Mega tier job done mate. Thanks! Cheers 🍻
thank you for these incredibly informative videos I really appreciate all the time put in to research all of this, it's truly incredible! I also love the small bits of humour you throw in :) Wishing you all the best!
Thanks very much! I really appreciate it.
another informative video - thanks! Looking forward to part 5 and especially part 6
Thanks much!
I keep coming back to your extremely thorough vids as references
(after having watched the entire series).
Most (all?) other reviews of water treatment systems assume that performance is the same for different systems, which is not even close to true, according to your excellent research. Thank you.
Thanks much! That’s basically what prompted me to dig into it. Reviews would just talk about price, usability, and things like flow rate…but never even touch on efficacy.
Years ago, when I had one too many failures of my UV water treatment pen, I switched to filtering. When I looked into it I remember concluding polio and hep-A were what I still might encounter. Since I already had my polio shots, I went and got the twinrix series of shots. I didn't know about rotavirus, so now I have another worry. I'm pretty sure I've already had the norovirus, so I hope I'm immune now (I don't want to go there again). I always carry some water treatment tablets, imodium and oral rehydration salts into the bush just in case.
Your presentations make this, sometimes complex, content easy to follow. Thanks for the monumental amount of research and preparation these videos must require.
You are most welcome, and thank you! I appreciate the kind words.
Incredible video. In depth, well informed, and with a high production quality. Your channel will grow real fast once just one of your videos goes viral, which seems inevitable.
Thanks very much! It is kind of you to say.
Within the Ultralight community he's already a legend. 63k views on his food video.
I just realized that you only have 6k views on this video! That is totally unfair and I will watch and like all of your videos.
Keep it up, it's very useful, you'll make it with this quality of material!
Thanks!
You good at what you do
Keep up with the great content
Wow ! Great stuff, best "review" videos I have seen.
Thanks very much!
As Usual .. INTENSIVE methodology .. WONDERFUL !
All of your videos have been 'studied' by me with rapt excitement when a new one comes out
..
The video lengths are GOOD
I feel they are more of a Follow Along Methodology, not a cat chasing a mouse over the keys of a piano
Thank you very much!
I spent a summer in high school as a camp counselor teaching wilderness survival. Each week I'd bring out an old beat up Worse Case Scenario Card Game, thanks for the dose of nostalgia
Very very very high quality, highly informative video going through and explaining all details and sources.
Thank you! Much appreciated.
WOW! Thanks.
fantastic! Love your detail and commitment to accurate research. Side note, have you ever looked at the Berkey Water Filters? I guess technically they can be classified as purifiers, but they are the true gold standard for the average person! And yes, they have a couple of small travel sizes as well.
Thanks! I did not know about their travel sizes. I will check them out!
Very informative. Thank you for really hunting down the references! Far to often people just go with “the public knowledge” or hearsay.
Thanks! I agree, and sometimes “public knowledge” can be wrong.
wow.....this video was incredible
Thanks!
Had a hunch viral risk would be the real kicker when it comes to high grade water treatment while hiking. Some of the most difficult to eradicate, yet more prevalent than chemical contamination and highly infectious. Even so I wasn't prepared for the statistics you dug up! Hardly ever seen concentrations like that outside of homeopathy before, it's almost enough to scare one into unnecessarily boiling water just for peace of mind, haha.
Really good series, personally never had to rely on surface water yet, but after a nasty experience with visible growths of _something_ in my camel pack's drinking tube I've been taking water safety a lot more seriously. Thinking about applying pasteurization even for water supplied at dedicated accommodation; twice now i've seen mosquito larvae swimming around in a glass of water I've poured myself... Makes me wonder what else I was chugging down while joking about "high protein water".
I must obviously owe my lucky good health to the sterilizing effects of the night's drinking after a full day in the field smacking rocks ;)
Ooo…protein water 🤢
Super!
I’m surprised you didn’t mention General Ecology First Need XL Elite water purifier. It’s under 200 bucks and has a fast flow rate. It is the only one I know that instructs you to occasionally perform a dye test to ensure the filter is working correctly. A tad bulky and the filters have gone up in price but, it’s been a go to piece of kit in my bag for 20 years! I even used it at home a few times during bad weather and a drought instigated low level in the cities water supply. Nasty water came out of the tap…amazing water once I filtered it.
The First Need is an adsorption filter, not an ultra filter. It gets mentioned in Part 5.
Thanks for the great effort you put in the researches for one single episode!!! 👍🏻... i still didn't find a satisfying conclusion if and how a charcoal filter or part can add beneficial properties to a system... Besides from the taste aspect...
Charcoal will be in the next video. It works by a different filtration principle. It’s coming though!
@@GearSkeptic excellent 😘
I use it already as non-chemical treatment if someone has stomach or diarrhea problems or in case of an intoxication...
I'm happy to lern more details 😘
Greetings from Taiwan 🙋🏼♂️🌴
AvE meets hiking gear love it.
Hiked this year a PCT section in Washington. There were multiple cases of virus stomach infection that immobilize hikers for days... Viruses are real threat in lakes and stale water sources...
WOW New Video 🤩Awesome Thank You 👏👏👏😁👣🐾🐾
😊
Excellent research. Thank you. Take a look at Tortoise Gear's SOLar Water bags. They take advantage of heat and UV radiation.
Good tip! I do have have some research for an eventual edition on solar disinfection. So easy to get sidetracked!
Some filter manufacturers state *nominal* and *absolute* particle size filtration. Sawyer has an S3 filter that they claim filters viruses. They just wont make that claim for the Sawyer Squeeze.
Since you've posted this video(2 years ago), Lifestraw has come out with(about a year ago) a gravity purifier system(Lifestraw Peak series gravity purifier) with a pore size of 0.02μm(same as the MSR). However, it has a 18000 liters, versus the 3000 liter life of the MSR Guardian Gravity Purifier. This Lifestraw purifier costs only $151 and change(at the time of this comment), but unfortunately is out of stock. A replacement Lifestraw purifier ultrafilter is only $84 and change but is on sale for $67 and change and it is in stock(again at the time of this comment). So this is what I did. I just ordered the replacement ultrafilters along with their necessary backflush syringes. Those backflush syringes are only included in the their Gravity purifier kit. I plan to adapt/improvise/jerry-rig these to work with my 3L Cnoc VectoX bags. Upon doing some calculations on the MSR Guardian gravity purifier vs the new Lifestraw Peak gravity purifier. Here's what it looks like. MSR=$0.30/gallon Lifestraw=$0.014/gallon. Both advertise the same flow rate. MSR advertises 0.5L/min where Lifestraw advertises at 30L/hour(aka the same flow rate) The only advantage MSR has over the Lifestraw, is the activated carbon element. The Lifestraw does not offer an activated carbon element for this purifier system. For that, you would need to adapt something like a Katadyn active carbon bottle adapter onto it.
As for the Sawyer point zero two purifier. I believe they still make them, however these aren't available for retail sale anymore. They only make them for their overseas non-profit philanthropy programs.
Good to know! Thanks much.
@@GearSkeptic Also, This was a very informative video and topic. Thank you.
So, I am a year late to the party. Wanted to say thanks for all your hard work. I tried to figure this all out on my own a few years back and found it incredibly confusing.
You are most welcome! I figured, after doing it for myself, I should share in case anyone else was interested..
Wow! I can’t believe I got all that for free! Thanks.
My pleasure! I only hope it helps.
Just for your interest/further research i found a quite old article from the journal of virology on using filtration to determine virus size. They talked about virus retention being highly influenced by adsorption. For them this was a problem they needed to adress, but for outdoor filtration this means that virus can be removed even if the pore size is quite bigger than the virus it retains. (DOI: 10.1128/JVI.2.1.21-25.1968)
I have no idea how well normal backflushing removes adsorbed virus, but as the article above talkes about high adsorbtion in salty solution and nearly no adsorbtion in hypotonic one, backflushing with purified water might remove all virus that binds to the filtration material.
This is just some food for thought i haven't researched more than an hour.
(also haven't watched the whole video yet. I went down a research rabbit hole and will proceed from minute 10:00 onwards now)
Thanks! I will check out that study. I’m knee-deep in adsorption and ion exchange stuff right now, for Part 5.
Another awesome video. Like others, we are accustomed to creators having merchandise/patreon/affiliate links to support the content. Even if you don't need the money, the service you provide is valuable. My suggestion is hiking apparel with your logo on it. I would happily pay $30-40 dollars for a quality long sleeve hiking shirt, or even a Nalgene bottle with your logo on it.
Thank you very much for the thought, but it is sort of a passion project for me, so no other reward than your kind comments is necessary!
Thank you very much for all your hard work, I'm betting you enjoy the research and it is apparent in the delivery.
I currently own a grayl ultralight and with all the info I cannot figure out whether to replace it - I was planning on a hydroblu with the screw on activated charcoal filter but with all this info I cannot figure out the best bet for the coast to coast in England next year as weight is a concern. The one take away I have nailed down though is boiling answers most of my problems but then more fuel is carried or do I just risk it with a Sawyer mini? Can't figure it out, the answers are here just need to watch it a few more times.
I break it down by considering which threats to worry about given the environment you’ll be passing through.
If you will only be drawing water from wilderness sources largely unaffected by humans, a bacterial filter like a Sawyer seems like an efficient choice.
If crowds of people use the waters, they can introduce viruses as a threat (like recreational areas with lots of swimmers).
If there is risk of contamination from industrial or agricultural activity, then chemicals might be an issue.
I usually bring a Sawyer for general use, and some chemical tabs for backup should I encounter bad water and have no choice. I’ve also always got the means to boil.
Since it’s light and small, I started carrying the Platypus carbon element in case the filtered water still smells or tastes bad, though I haven’t actually bothered to use it yet. I did buy one of the Hydroblu elements to try out, though.
If you’ll need to source water from farm or urban runoff, or from water where motor boats can leave chemicals, I’d stick with your Grayl.
Hope that helps!
@@GearSkeptic It certainly does, thank you once again, even your comments are comprehensive!
Cheers
Midway through this video I decided to look up the specs for my Platypus Gravityworks filter, which led me to the website of the company I bought it from, Mountain Equipment Company (formerly Co-op). MEC's specs for this and other filters come with the note "Most viruses are in the 0.1 micron size range, but they can be as small as 0.002 microns." nooooooo 😭(I contacted MEC about the inaccuracy!)
Sometimes the website people are not the spec people 😉
Your voice kind of reminds me of the man who used to narrate unsolved mystery’s lol
I also wonder if viruses get through via manufacturing defects that allow some water to go around the filter. Forthe life of me, I actually started wondering if there might be random radiation events putting larger holes in the filters. Gosh Darn Cosmic Rays at it again.
Don’t forget the wormholes!
Buddy you’re killing me which of the top three water filters we should be using for backpacking and Hunting?
Your videos have made me so much more informed on information I would never have had the time to put together. This channel is worth it's weight in gold. Unfortunately for your bank account, digital assets don't have weight. Hope my likes and subscription are enough to keep the lights on.
Thanks much! Very kind of you.
I’m not actually signed up for the affiliate program, so YT gets whatever the ads make. I had originally intended to stay ad-free, but they changed the user agreement a year or so ago, and now they can put ads in for their own sake. I suppose that’s fair. They do provide this service for free!
@@GearSkeptic Your donation to the community is what all good creators aspire to do. If you ever decide you want to be compensated for your efforts, a 3x5 pocket sized notebook field guide would be a great way to publish this info and sales would help cover costs to invest back into the channel. Even if its a print on demand file that people buy for a few bucks, it would cut down on your costs. I think it would leave a lasting impression on the community of backpacking and hiking as your methodical approach is sorely missed in many hobbies. I personally have used your info to overhaul my emergency gear and look forward to a possible guide on carrying water and maybe footwear, the largest items people usually have to contend with. My goal to hike the Appalachian trail is a slow burn and your channel has made it seem possible.
Fortunately, I have a ton of ideas in the queue. Unfortunately, I’m super slow, so it’s gonna take a while!
17:32 The Purifiers: Specs
($200+)
My guardian only lasted one season the housing cracked on day 16 on the JMT MSR fixed it but still worried about the housing design. The housing is a 2 part mold and it split at that seam.
Hmm. That’s a bit concerning. Something to keep in mind.
I guess measuring virus dimensions is 'old science' It already featured in school textbooks by the end of the sixties. Stuff of legends, myths and fables these days.😂 Teriffic stuff. Many thanks.
Of the people I’ve talked to and hiked with that have either Thru hiked or section hiked the AT who contracted Giardia or Norovirus, they all used either Sawyer Squeeze or Katadyn water filters. I always assumed that they drank infected water even tho they filtered it. If your synopsis is correct, they didn’t get it from filtered water? Can it be airborne as well and inhaled? I’m thinking it’s nasty hands (poor hygiene).
Cause and effect can be tricky. Lots of things could be happening.
Those two filters are pretty good, unless you’re facing viruses. Many seem to assume viruses aren’t a threat in the States, but they are out there in some places. It could explain why some still get sick despite filtering (with devices only good down to bacteria).
As you say, hiker hygiene is also a culprit. Many of the researchers from the studies I’ve found agree. And, how you use the filter (and handle dirty water) could be an issue. Some folks don’t use good “lab practices” with handling contaminated equipment.
Your hand acting skills are second to no one 😂
Never had a day of training! 🥸
I love you
this shit was so good cracked me up thanks for the entertainment i love it
You’re welcome! 🤓
Why would a 0.1 micron "microfilter" like the sawyer mini offer superior protozoa reduction to a 0.02 micron "ultrafilter" like the guardian? For that matter, why would any microfilter offer superior bacteria reduction rates vs protozoa if protozoa are generally larger organisms? What other factor is at play besides size exclusion that leads to this result?
Maybe I missed it but havae you evaluated Steripens as an option for water treatment?
Not yet! I have UV and solar disinfection planned for Part 6.
I hope you're getting paid to lecture in some other part of your life, because you're better at it than most of the professors I've been exposed to in my life (and that includes medical school).
Thank you very much! Those are kind words, and I do appreciate them!
How do you store filters so they don’t grow mold or get nasty from sitting. Is it even a problem I should worry about?
They can grow mold. Sawyer recommends giving them a diluted bleach backflush and then letting them dry out on their own (don’t seal it in a ziplock bag).
Hey I’ve got a question!!
Filters like the Hydrblu MUV 3 and the Epic Nalgene filters claim to remove viruses, and both seem to be using an adsorption technique of sorts. If this was the case, there would be no way to know if the filter was going bad. BUT, they both also say that the filter flow will slow down and thats how you will know it should be changed. This doesnt seem to add up? How can I know? Ive been using the MUV3 for my daily tap water for a year now and it has hardly slowed in flow.
That's usually because most filters with an adsorption element are also using a traditional filter for the bigger stuff. So, that filter will tend to clog like any other and reduce flow. You sort of have to trust them that the filter will clog and slow at a rate matching the saturation of the adsorption media, however.
I guess it may be time to turn in the old filter and use a frontier max- thanks
W vid
I don’t understand trying to find the source information of a decades-old book. A 5-second Google search takes you to NIH sources. Still love your work, though.
It relates to the logical problem that you can't prove a negative. In this case, the negative statement is: "There are no viruses 4nm in size." That can't be proven directly. The only thing you can do is try to look up every single virus known to science, in order to establish a list showing how everything is larger than that. There's no single-search I'm aware of that will do that for you.
The problem is, you can never be sure there isn't a 4nm virus out there that you just didn't catch. There might be one documented in a source outside the NIH. There might be hits that didn't come up with your particular search terms, or via the engine you used to search with. Logically, it always remains a possibility.
So, proof-wise, the better approach is to try and establish the truth of the positive version of the position: There is a 4nm virus. Not only can that be proven conclusively, it would have been the much faster way to go. One 5-second Google search that returns an electron microscope measurement of 4nm and you're done!
The problem is, that quickie search returns no hits. This doesn't prove the negative, though. It just fails to prove the positive. So, you end up faced with two choices: 1) try to prove the positive by tracking down the source of the factoid in the book, or 2) go the much, much longer way of trying to play process-of-elimination with the sizes of every known, human waterborne pathogen ever identified.
It might seem like simply Googling "world's smallest virus" would suffice. It doesn't. The distinction "world's smallest" changes over time. Any given article you might find claiming the record could have since been superseded. It could also just be wrong. I found articles claiming Tobacco virus was the smallest, but knowing better I kept searching. Sure enough, I found Porcine virus was smaller still. That was the smallest I could find, but there could always be some other virus out there that was recorded as one nanometer smaller. And, another one smaller than that.
Basically, establishing the truth of the positive statement would have been both more conclusive and faster...if it had panned out. Unfortunately, it didn't. So, I ended up having to do it the hard way after all.
Oooooohhhhhh yeeeeeaaah