13 ms·

The experiment that proved airborne disease transmission

171 points by pabo 6y ago

redis_mlc 6y ago
The article is from July 17, 2020. People wonder how ancient civilizations fell, but with worthless information like this after 5 months (July) of the US lockdown, it becomes apparent: "Especially until effective vaccines and antiviral treatments are developed, Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19." So how do you actually disinfect enclosed spaces nationwide? Is anybody doing that? (I'm a proponent for herd immunity, like all other flu viruses, but other people desire more concrete actions - yet that isn't happening, and we are building herd immunity as the default outcome.)
- deleted 6y ago
  [deleted]
- sebmellen 6y ago
  There are plenty of viable ways to disinfect closed spaces, like cold plasma generation [0] or UV light disinfection [1]. [0]: https://drexel.edu/now/archive/2020/April/cold-plasma-filter-covid-19/ https://drexel.edu/now/archive/2020/April/cold-plasma-filter... [1]: https://www.cnet.com/health/can-uv-light-protect-you-from-covid-19/ https://www.cnet.com/health/can-uv-light-protect-you-from-co...
- _Microft 6y ago
  Why bother to disinfect when you can ventilate? Air with pathogens out, fresh air without pathogens in. (Regarding herd immunity: you're aware that at the current rate of 55000 people per day, it would take 10 years to infect 60% of 320 million people? Nothing to say of the countless casualties that you would get in the process.)
  - nradov 6y ago
    Since eradicating the virus has become impossible, most national governments are currently pursuing a herd immunity strategy by default. They're just doing it at slightly different rates. In the USA the current daily rate of confirmed new cases is about 43000, not 55000. However there are a large number of "dark matter" cases not counted in official statistics. About 40% of infections are asymptomatic, and many more are paucisymptomatic. Most of those patients never get tested.
    - _Microft 6y ago
      What countries are actually following a strategy to reach herd immunity by having "enough" people fall ill and hopefully recover (having "recovered" does not preclude persisting damages btw!)? Most countries are rather waiting for a vaccine to become available and try to minimize the number of sick and dead in the meantime without interfering with economy too much. (54.4k was number of newly confirmed cases on friday 10/2 by the John-Hopkins University btw. I'm aware that the US has inadequate testing [0] and that the real number is going to be a lot higher than this. [0] https://ourworldindata.org/coronavirus-testing#the-positive-rate-a-crucial-metric-for-understanding-the-pandemic https://ourworldindata.org/coronavirus-testing#the-positive-... )
      - nradov 6y ago
        Only New Zealand, Taiwan, Vietnam, and maybe a couple other countries are actively avoiding herd immunity. Regardless of their public statements, other countries aren't actually trying to minimize the number of sick and dead. The public health measures in place are generally insufficient to contain the pandemic, so I predict that many areas will reach a significant level of herd immunity before a safe and effective vaccine is widely available. We won't know whether that prediction is accurate until about a year from now.
      - xorcist 6y ago
        A vaccine is unlikely to wipe out the virus for good. They just aren't that effective. We can't wipe out other coronaviruses or the common cold by vaccination even if we wanted to. It will continue to circulate in the population, just in a less explosive manner. This also means it is possible we will never reach herd immunity in some absolute sense much like we haven't for other coronaviruses.
  - function_seven 6y ago
    Probably cheaper to slot a component into your HVAC than it is to re-engineer it to draw outside hot air, cool it, and still keep interiors at a comfortable level. (Reverse for winter) My house has a fantastic filter along with a UV system as well. When I bought the house I thought it was overkill, but now I’m quite happy it’s there.
    - _Microft 6y ago
      The amount of heat in the air is small compared to that in other materials; buildings with stone or concrete walls have a sufficient heat capacity that you can ventilate without temperature changing too much. This works less well for buildings with wooden walls though. Ventilating properly requires discipline though. No tilted/semi-opened windows for prolonged time for example. In winter, heating should be turned off and the windows should be as wide open as possible to minimize the time to exchange air. That's to reduce the loss of heat. 5-10 minutes of ventilating is good enough, usually. We usually don't have air condition here, so I don't know what's the recommended process in the summer. It's common to ventilate like this in Germany in the winter for example. I know (now returned) former German expats that completely missed this development. They still tilt windows and let the heating run all day long.
  - redis_mlc 6y ago
    US buildings are designed to recirculate most air for energy cost reasons. Ventilation sounds like a good idea, but it doesn't match how things work today because of how stale the air becomes. (That's why in Silicon Valley large companies have "air consultants" measure the freshness twice per year and report the rate. I've talked to some.) So my question stands on how and what to do to have more effective air circulation indoors, and what else we should do. And why is this conversation only happening several months into a lockdown. It's as if American government is falling down from learned helplessness.
- smarx007 6y ago
  Thankfully you missed that the article discusses history from 1956 regarding the airborne transmission study methodology. Otherwise you might have gotten a heart attack. Goodness!
- Zenst 6y ago
  I was thinking HEPA filtration may already cater for virus's, but with HEPA certification being .3 microns and the COVID-19 virus 0.12 microns, then it gets down to individual air conditioning systems. Some may use ionising in combination or UV. So I foresee a whole raft of legislation and requirements for office spaces ahead. Which will only help drive the work from home long-term as cheaper office space. But also help shift us away from open plan offices that I've never met anybody who liked. As for herd immunity - that really is best effective against viruses that do not mutate that quickly. Corona-viruses from my understanding, do mutate. Though it is often the case that mutations of a virus over time lean towards mutations that make them less impacting upon the host. Which may be down to natural selection in that those with no impact can spread it more and no virus really wants to kill the host. Impacted/dead hosts tend to be less effective in transmission. So may very well be down to that aspect in why they tend to become less impacting. On the UV aspect https://www.nature.com/articles/s41598-020-67211-2 https://www.nature.com/articles/s41598-020-67211-2 a UV wavelength of 222nm that is effective against the virus and safe for humans. Though how stable current UV output is and by that if you had a 222nm light, over time would that drift and become less human safe is something I'd want to check. There again - flu's and colds are more prevalent during winter months when we have less sun and less UV. Can't ignore that pattern.
  - nradov 6y ago
    All viruses mutate, but so far SARS-CoV-2 has been mutating relatively slowly. It has an error correction mechanism which blocks the majority of mutations. By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year. The human species already has a significant level of herd immunity against four other endemic coronaviruses. The same thing will eventually happen with SARS-CoV-2 one way or another, but hopefully we will have an effective vaccine soon enough to accelerate that process while minimizing the death toll.
    - beagle3 6y ago
      > By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year. That's true, but that might change soon (the "every year", not the mutation speed): Results of [0] are supposed to be published this quarter. I am hopeful for them to be positive. [0] https://www.biondvax.com/2020/07/last-of-12400-participants-completes-final-visit-in-biondvaxs-m-001-universal-flu-vaccine-pivotal-phase-3-clinical-trial/ https://www.biondvax.com/2020/07/last-of-12400-participants-...
- krimeo 6y ago
  And remember all that "all scientists say masks dont work, why are you wearing a face mask, are you stupid?" only to change to the exact opposite in may/june ?
  - mieses 6y ago
    They started wearing masks which reduced their blood oxygenation and made them even stupider.
sharpercoder 6y ago
Can ultra-high resolution, ultra-high framerate and ultra-high zoom camera's measure exhalation of virii particles out of a humans mouth?
- pvg 6y ago
  Most viruses are smaller than visible light wavelengths. The biggest are about a wavelength or two. Edit: some sizes here, including SARS-CoV-2 https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-Compared-to-Other-Things.aspx https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-C...
- praptak 6y ago
  Resolution of plain optics only goes up to the diffraction limit, which is not enough to see a virus. Then there are super-resolution techniques which can go beyond that, but I don't think any of them could be adapted to scan the vicinity of the coughing human in real time.
- fulafel 6y ago
  The virus is quite small and would have to be in some unconventional state to show up optically (could make an interesting what-if xkcd).
calibas 6y ago
It seems the reasoning by officials is, "Yes, it's airborne, but there's not enough N95 masks for everyone so we don't want to cause panic or an N95 mask shortage for doctors and nurses by admitting it's airborne."
- dboreham 6y ago
  Also supposedly if a disease is declared airborne then hospitals have to adopt various isolation measures beyond just N95 that are very costly. This may be the reason the powers that be won't announce airborne transmission until after the pandemic is over.
  - shalmanese 6y ago
    We make fun of medieval medicine but look at this shit! We're pretending that saying some magic words has an effect on a physical reality of disease spread! Who says that saying its airborne "has" to mean that certain procedures have to be adopted? That's not a rule of the universe, it's a rule that humans came up with and agreed upon and humans have the power to fix. We distilled down a set of physical principles into a set of guidelines, forgot the underlying physical principles and now operate purely in the world of the manmade guidelines, totally oblivious to when the guidelines are no longer reflecting the physical reality.
    - sokoloff 6y ago
      Unless you say something like “look it’s airborne but that fact shall not be admissible into any future lawsuits on any topic” (and have certainty that that will stand up to review), I’m not sure you can fully equate to the current “it’s not been declared to be airborne transmissible.”
    - jchw 6y ago
      While I understand the frustration, the reality is we shouldn’t be making fun of either. Just because the end result of something is inarguably “stupid” does not mean that any of the things that went into it are “stupid.” To do the Hacker News thing and make a bad analogy to computer science topics in a totally irrelevant thread, this is how I view a lot of stuff people complain about these days (think JavaScript, or Electron apps.) Real life is hard. To be a bit more concrete, consider the following: if you have a system where people are not encouraged to follow the rules as written, they will work against the spirit of what is written as well as what is actually written. If you have a system where people are discouraged from not following the rules, they may still engage in things that do not follow the spirit or written rules, but there is some accountability. But you can also try to work around what’s written to follow the intent as well, and I think that is where you get weird, counterintuitive, “stupid” results that can still “make sense” (as opposed to clearly corrupt cases where it is “stupid” and also does not make sense.) I think people, especially literal minded as many here are, prefer concrete rules. But the knock-on effect is that its not easy to simply proclaim they’re made up any time it’s inconvenient, and it really shouldn’t be. Perhaps, in fact in my opinion, definitely, the “escape hatches“ for when rules don’t work out practically are broken, but I still do prefer having rigid standards, especially for health. Hopefully, although it is probably not going to happen, organizations can have some postmortem-style reflections on what went wrong, so that hopefully next time we can be better prepared. History loves repeating though, so, you know.
lucb1e 6y ago
TL;DR: the actual experiment: > they constructed an air-tight closed ventilation system that connected a six-room tuberculosis ward to an exposure chamber with 150 guinea pigs. (Among rodent animal models, only guinea pigs could cough and sneeze, making them ideal for studying how respiratory diseases spread.) The guinea pigs were exposed to the infected air over a four-year period. A second group of 150 guinea pigs acted as controls: their air ducts were irradiated with UV-C lamps to kill TB bacilli. Results: > an average of three guinea pigs per month contracted TB, while no controls were infected. The experiment [also] quantified how many TB infections could be expected to result from exposure to a given number of patients over a defined interval. Relevance to COVID-19: > Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19
- nostromo 6y ago
  Today I learned: > The animals were used so frequently as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject. https://en.wikipedia.org/wiki/Guinea_pig https://en.wikipedia.org/wiki/Guinea_pig
  - ISL 6y ago
    In the same spirit, I offer Tami Knight's Avalanche Poodle: https://www.snowmediazone.com/the_zone/data/500/medium/Avi_poodle.jpg https://www.snowmediazone.com/the_zone/data/500/medium/Avi_p... Among my friends, to go first in an uncertain situation is sometimes called, "poodling it".
  - dehrmann 6y ago
    Same for lab rats.
- contravariant 6y ago
  Some things worth pointing out about the linked article (not by Riley), regarding masks and disinfecting air: https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.096214 https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.0962... - It contains no experimental data, it's a review of possible methods. - It's not about Covid-19, although that's to be expected. - The masks it talks about are N95 and N100 respirators (which it notes aren't in adequate supply). Some interesting quotes: > If one assumes that influenza is transmitted by respiratory droplets [..] rather than by aerosols [..], the supposition may be that keeping a safe distance may obviate the need for a mask. It is stated that the range of such droplets is generally no more than 3 ft. We are unable to locate the basic science behind that assertion. > Whether contagious as a respiratory droplet, aerosol, or both, there have been no controlled studies to investigate the efficacy of respirators in preventing the transmission of influenza A > there is a theoretical problem in the logic underlying N–95 respirators. Assume an N–95 mask functions better than its rating and at a sedentary inhalation rate blocks 98% of the bioaerosols that it is confronted with. We are still left with the 2% that penetrate through the filter, to be inhaled by the wearer. Whether discussing tuberculosis, influenza, measles, or smallpox, we do not know the concentration of pathogenic bioaerosols in the environment, nor do we know the minimum infectious dose for these pathogens. Anyway I don't think anyone disagrees with their conclusion that having everyone wear N100 masks is a good idea, but I'm not sure if any of their proposed methods are feasible. And the most important conclusion of their research is perhaps that we know way too little about possible countermeasures.
trhway 6y ago
> ultraviolet-C disinfection technology for air purification systems that were installed in health care facilities, factories, and NASA space capsules. Today, this technology is being used in Shanghai, Moscow, and New York City to protect subway and bus passengers against SARS-CoV-2, and China is also using the technology to disinfect hospitals Russian FSB has just arrested (on secret state security charges) on his short trip back home from China a top high voltage systems specialist who has been working for the last two decades on UV water and air cleaning system in South Korea and China. Seems it is becoming a sought after hot tech in the current situation.
- thaumasiotes 6y ago
  Any kind of air cleaning is relevant, and in demand, in China. Unfortunately, air purifiers have embraced the situation by demanding luxury pricing.
lifeisstillgood 6y ago
UV-C lights that irradiate an air duct is literally the most surprising (and in retrospect obvious) thing I learnt today. Is this something a household HVAC could be upgraded to. Do HNers in areas that have air con think it's a "yeah people will want that" idea?
- TheSpiceIsLife 6y ago
  What magnitude of irradiance is required? If the required power is,say, 500w continues, or more, that's going to get quite expensive to run. For example, where I live running a 500w device 24/7 is going to add an extra $1100 a year to the power bill.
  - tzs 6y ago
    Looking at germicidal bulbs at 1000bulbs.com, the highest wattage bulb they have is 65 watts [1]. Most are well under that. Looking at random in-duct systems, it looks like they range from 1 to 10 or so bulbs with the later being for commercial buildings. Home systems seem to lean toward 1 or 2 bulbs of maybe 20ish watts or so total. This site [2] says typically $15-30 per year energy cost [1] https://www.1000bulbs.com/product/113917/AU-LG64T5L.html https://www.1000bulbs.com/product/113917/AU-LG64T5L.html [2] https://www.pickhvac.com/faq/hvac-uv-lights/ https://www.pickhvac.com/faq/hvac-uv-lights/
- ajsnigrutin 6y ago
  I always wondered just how much UV-C do you need to effectively kill the virus (power vs duct diameter and air speed).... because, instead of traditional masks, you could take a small fan, blow air into a pipe with a UV-C bulb inside, and pump the sterilized air to the human... basically something like this: https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop
  - Gibbon1 6y ago
    I tried looking into that this spring. I suspect the answer is for this virus not much. Nothing to indicate that any part of it's life cycle involves hanging around latent. Interesting bit on how UV-C works to sterilize. https://en.wikipedia.org/wiki/Pyrimidine_dimer https://en.wikipedia.org/wiki/Pyrimidine_dimer Interesting thing bacteria and some viruses have DNA repair enzymes that can fix damage from UV-C. Medically you're always bedeviled by bacterial and fungal spoors. Limitations with UV-C sterilization I think prevents wider use. Not a magic bullet. Though it probably works well for influenza, colds, and this bat virus.
ajb 6y ago
Ok, dumb idea time: suppose that everyone in an office sits on a chair that raises their body to X volts. At the same time a collector mesh is provided at each desk, at -X volts, but shielded so that you can't touch it and shock yourself. What X is large enough to ensure that all the virus particles you cough out end up at the collector? Is it possible to do this without electrocuting everyone?
- deleted 6y ago
  [deleted]
- vimax 6y ago
  that sounds kind of like what an ionized air purifier does
- imposterr 6y ago
  Free electrons tend to distribute themselves on an object as to minimize the repulsive forces between them. This usually means that they distribute evenly on the surface of objects. Humans are a bit more complicated in structure than say a metal ball, but my guess would be that there would be a similar situation where all the free electrons would just build up on the skin. Therefore, I don't think the particles one would cough up would be negatively charged.
  - enchiridion 6y ago
    Would the particles get charged as they pass through the later of electrons?
  - curryst 6y ago
    Alveoli are basically small air sacs in your lungs, so they're a surface (it's just an inverted ball, a hollow sphere in a not-so-solid object). No idea how that influences where the electrons go. I wonder how the nervous system would interact with that as synapses fire. I'm curious if they would build up, or if the synapses all over the body firing would make them bounce around constantly.
    - 6y ago
praveen9920 6y ago
Can we "mutate" a virus to use radioactive isotope of carbon (c-14? something that is not harmful for humans) so that we can observe how viral a virus is? Not an expert on radio isotopes or spectrography or viruses. Note: I know, radioactive virus at this point might freakout people a little.
- koeng 6y ago
  AFAIK there aren’t methods to do that in vivo, unfortunately.
- ISL 6y ago
  No need. It mutates itself. The propagation of genetic strains of Covid-19 can be viewed here: https://nextstrain.org/ncov/global https://nextstrain.org/ncov/global Our ability to do this for every single Covid-19 case in the universe is, I imagine, limited only by funding/infrastructure/training.
- globular-toast 6y ago
  Where would it get the carbon-14 from? Virus particles (virions) are made by and from their host. So you'd need a human made from carbon-14 first.
- Jabbles 6y ago
  We basically already know how viral viruses are because they undergo mutations, and we can trace which strain people have and where they caught it from by sequencing their DNA (technically RNA) and looking for the virus's "ancestors". See for example https://www.eurekalert.org/pub_releases/2020-10/du-gt100120.php https://www.eurekalert.org/pub_releases/2020-10/du-gt100120.... Also you wouldn't mutate a virus with C14 or similar radiactive isotope, because that can't be encoded in its genetics, and such a virus would use any old Carbon atom (most likely normal C12) to replicate. Finally, mutating a virus and releasing it seems ethically dubious in the middle of a pandemic...
lootsauce 6y ago
Ok dumb question why don’t we settle the question by conducting the experiment for covid19?
- hurrynot 6y ago
  The article says the TB experiment ran for four years. It isn't clear that you need four years to prove airborne transmission, but it is likely that you need a lot of time.
- RogerKamben 6y ago
  It's pretty much settled also for sars-cov2. A study in China found the virus in air samples taken inside the central air-condition system, far away from any patients (see bottom). Another found correlation between infected and where they were sitting vs AC duct outlets. Also the fact that mandatory masks have had zero effect on the R value in any country, same as for influenza and other "flu" viruses. If it was spread by droplets/surfaces then masks should at least have some effect to slow or contain the spread, like make a dent in the curves. Yes there are masks that prevent TB transmission but this bacteria is more than 10x larger than typical respiratory viruses. They look like duck beaks, are very uncomfortable and require training to use properly. I haven't seen these anywhere during this pandemic and they wouldn't help either as they are designed to prevent aerosols down to about 2um size. There is plenty of space for ~0.1um viruses even in 0.5um droplets. Some researchers even claim the virus can stay potent a while after the droplet evaporates and float around like dust. CDC meta study showing medical masks had no effect neither as PPE or source control: https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article Study comparing medical masks and N95 masks found no difference in transmission of influenza: https://pubmed.ncbi.nlm.nih.gov/31479137/ https://pubmed.ncbi.nlm.nih.gov/31479137/ More links and summaries collected here: https://swprs.org/face-masks-evidence/ https://swprs.org/face-masks-evidence/ This Time article has lots of links and info (but the argument for masks is complete fail): https://time.com/5883081/covid-19-transmitted-aerosols/ https://time.com/5883081/covid-19-transmitted-aerosols/ It's funny how some claim we didn't need masks before, but now we need them since it's spread by aerosols?? The truth is in fact the opposite and don't get me started on cloth masks...it's absurd. This seems more like covering their asses than following the science. Most of these studies involve health personell, with high-end masks, the general public will of course do much much worse. This survey of studies and history of mask use in dentistry is also informative (why was it taken down?): https://archive.is/My2jr https://archive.is/My2jr The WHO reversal on mask use is also revealing: On July 12, Deborah Cohen, the medical correspondent of BBC2’s Newsnight, revealed on Twitter that: ‘We had been told by various sources [that the] WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying.’ She said the BBC had then put this to the WHO, which did not deny it. In March, the WHO had said: ‘There is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can protect them from infection with respiratory viruses, including Covid-19.’ -Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564-7. -Fears AC, Klimstra WB, Duprex P, Weaver SC, Plante JA, Aguilar PV, et al. Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions. Emerg Infect Dis 2020;26(9). -Chia PY, for the Singapore Novel Coronavirus Outbreak Research T, Coleman KK, Tan YK, Ong SWX, Gum M, et al. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nat Comm. 2020;11(1). -Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerg Infect Dis. 2020;26(7). -Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center (pre-print). MedRxiv. 2020 doi: 10.1101/2020.03.23.20039446. -Zhou J, Otter J, Price JR, Cimpeanu C, Garcia DM, Kinross J, et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.24.20110346. -Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature. 2020;582:557-60. -Ma J, Qi X, Chen H, Li X, Zhan Z, Wang H, et al. Exhaled breath is a significant source of SARS-CoV-2 emission (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.31.20115154. -https://pubmed.ncbi.nlm.nih.gov/19797474/ https://pubmed.ncbi.nlm.nih.gov/19797474/ -https://pubmed.ncbi.nlm.nih.gov/19216002/ https://pubmed.ncbi.nlm.nih.gov/19216002/
dmix 6y ago
This quote from the report should be top of the list of the lesson-learned from this COVID pandemic: > The current guidance from numerous international and national bodies focuses on hand washing, maintaining social distancing, and droplet precautions. Most public health organizations, including the World Health Organization (WHO) [16], do not recognize airborne transmission except for aerosol-generating procedures performed in healthcare settings. Hand washing and social distancing are appropriate but, in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people. This problem is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation [17] relative to the number of occupants and extended exposure periods (as graphically depicted in Figure 1). For example, airborne transmission appears to be the only plausible explanation for several superspreading events investigated that occurred under such conditions [10], and others where recommended precautions related to direct droplet transmissions were followed. Indoor contact, proper veneration, etc causing super-spreader events. Meanwhile here in Canada they waited until late May to even recommend wearing a mask in such situations (other countries like the US had similar time frames and Dr Fauci openly admitted they withheld this recommendation for the benefit of healthcare workers). https://www.ctvnews.ca/politics/it-s-now-recommended-that-canadians-wear-face-masks-1.4946752 https://www.ctvnews.ca/politics/it-s-now-recommended-that-ca... Much like drug prohibition and other grand social control experiments, I'm not convinced the value of being vague or simply straight up not recommending masks in order to keep supply chain available for healthcare workers was ultimately worth the downside. If supply chains was the issue then spend the government law enforcement power controlling and directing the supply chain for medical quality masks. This 4 month experiment (and I'm being generous there) where Feb, Mar, Apr and most of May they spent creating confusion and not recommending masks ultimately did more harm than good. Now pundits and online commenters love to attack these anti-mask people when for much of the year expert sources were far from making masks the recommended choice. Including gov-delivered misinformation about their utility in order to explain themselves. If the pro-social control (ie, lying the public) group thinks it was really stopping the wealthy and connected from completely ignoring these guidelines, then they are lying to themselves. As always with these gov poppet-mastery policies the only losers were the lowest common denominator poor people. Plenty of which still don't funny trust masks. I would have rather spent four+ months explaining the virtues of masks and explaining the supply problem honestly. Than playing catch up last minute. The fact Asia who had adopted masks, and never spent any time lying or dodging their public on their utility, have done better than western countries is no surprise. Asian countries had masks well before COVID. The older I get the more cynical I become about government and intelligentsia 'we know whats best', that includes withholding information (something extra popular in healthcare). All information should be as transparent as possible, regardless of fantasies of controlling it.
tech6 6y ago
I have an ozone vegetable washer. Is it dangerous to be in same room when this vegetable washer is running ? I can smell the odour of ozone near the vegetable washer
- ficklepickle 6y ago
  The odour detection threshold is 0.005-0.02 PPM. OSHA says less than 0.1 PPM over an 8-hour period. So you can smell ozone well before it is in the harmful range. Some air circulation wouldn't hurt while the device operates, but napkin math says you are OK.
pbreit 6y ago
Was there any doubt?
- globular-toast 6y ago
  Yes. A very quick, less than a minute, skim of the article would tell you that.
pa7x1 6y ago
The idea of respiratory viruses not being airborne sounds silly. What's the viral charge supposed to do, not jump into droplets smaller than certain size? Of course they are present in the smallest droplets! They are present in the mucous secretions of the infected individual and they will get expelled through the big and the small droplets. The distinction shouldn't be a qualitative one, airborne vs not airborne. It's a quantitative one, sufficiently infectious viruses may pose a risk at much smaller doses, the kind that you may be exposed by the smallest droplets expelled that simply stay afloat. It's also worth noting that human immune response is a complicated beast, what may not be infectious for an average healthy individual may put down someone with a weakened immune response. So even supposedly "not airborne" viruses that are very unlikely to infect the average healthy individual at very small doses may pose an "airborne" risk for individuals with a weakened immune response. There are more factors in all of this, atmospheric conditions may play a role. For example, cold temperatures may be more suitable for the virus to remain infectious outside of a host, thus increasing the likelihood of "airborne" propagation. TL;DR: The distinction between airborne and not airborne viruses is an artificial one. That only makes sense statistically for an average individual at certain atmospheric conditions for a concrete strain of the virus. But as any real-world statistical distribution there are tails and you will find "airborne" qualities for pretty much any respiratory virus in those tails.
temptemptemp111 6y ago
Bogus "experiment" - happy to debate anyone on the topic, but I'm sure they'll just censor my proof.

171 points by pabo 6y ago

The article is from July 17, 2020. People wonder how ancient civilizations fell, but with worthless information like this after 5 months (July) of the US lockdown, it becomes apparent: "Especially until effective vaccines and antiviral treatments are developed, Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19." So how do you actually disinfect enclosed spaces nationwide? Is anybody doing that? (I'm a proponent for herd immunity, like all other flu viruses, but other people desire more concrete actions - yet that isn't happening, and we are building herd immunity as the default outcome.)

deleted 6y ago
[deleted]
sebmellen 6y ago
There are plenty of viable ways to disinfect closed spaces, like cold plasma generation [0] or UV light disinfection [1]. [0]: https://drexel.edu/now/archive/2020/April/cold-plasma-filter-covid-19/ https://drexel.edu/now/archive/2020/April/cold-plasma-filter... [1]: https://www.cnet.com/health/can-uv-light-protect-you-from-covid-19/ https://www.cnet.com/health/can-uv-light-protect-you-from-co...
_Microft 6y ago
Why bother to disinfect when you can ventilate? Air with pathogens out, fresh air without pathogens in. (Regarding herd immunity: you're aware that at the current rate of 55000 people per day, it would take 10 years to infect 60% of 320 million people? Nothing to say of the countless casualties that you would get in the process.)
- nradov 6y ago
  Since eradicating the virus has become impossible, most national governments are currently pursuing a herd immunity strategy by default. They're just doing it at slightly different rates. In the USA the current daily rate of confirmed new cases is about 43000, not 55000. However there are a large number of "dark matter" cases not counted in official statistics. About 40% of infections are asymptomatic, and many more are paucisymptomatic. Most of those patients never get tested.
  - _Microft 6y ago
    What countries are actually following a strategy to reach herd immunity by having "enough" people fall ill and hopefully recover (having "recovered" does not preclude persisting damages btw!)? Most countries are rather waiting for a vaccine to become available and try to minimize the number of sick and dead in the meantime without interfering with economy too much. (54.4k was number of newly confirmed cases on friday 10/2 by the John-Hopkins University btw. I'm aware that the US has inadequate testing [0] and that the real number is going to be a lot higher than this. [0] https://ourworldindata.org/coronavirus-testing#the-positive-rate-a-crucial-metric-for-understanding-the-pandemic https://ourworldindata.org/coronavirus-testing#the-positive-... )
    - nradov 6y ago
      Only New Zealand, Taiwan, Vietnam, and maybe a couple other countries are actively avoiding herd immunity. Regardless of their public statements, other countries aren't actually trying to minimize the number of sick and dead. The public health measures in place are generally insufficient to contain the pandemic, so I predict that many areas will reach a significant level of herd immunity before a safe and effective vaccine is widely available. We won't know whether that prediction is accurate until about a year from now.
    - xorcist 6y ago
      A vaccine is unlikely to wipe out the virus for good. They just aren't that effective. We can't wipe out other coronaviruses or the common cold by vaccination even if we wanted to. It will continue to circulate in the population, just in a less explosive manner. This also means it is possible we will never reach herd immunity in some absolute sense much like we haven't for other coronaviruses.
- function_seven 6y ago
  Probably cheaper to slot a component into your HVAC than it is to re-engineer it to draw outside hot air, cool it, and still keep interiors at a comfortable level. (Reverse for winter) My house has a fantastic filter along with a UV system as well. When I bought the house I thought it was overkill, but now I’m quite happy it’s there.
  - _Microft 6y ago
    The amount of heat in the air is small compared to that in other materials; buildings with stone or concrete walls have a sufficient heat capacity that you can ventilate without temperature changing too much. This works less well for buildings with wooden walls though. Ventilating properly requires discipline though. No tilted/semi-opened windows for prolonged time for example. In winter, heating should be turned off and the windows should be as wide open as possible to minimize the time to exchange air. That's to reduce the loss of heat. 5-10 minutes of ventilating is good enough, usually. We usually don't have air condition here, so I don't know what's the recommended process in the summer. It's common to ventilate like this in Germany in the winter for example. I know (now returned) former German expats that completely missed this development. They still tilt windows and let the heating run all day long.
- redis_mlc 6y ago
  US buildings are designed to recirculate most air for energy cost reasons. Ventilation sounds like a good idea, but it doesn't match how things work today because of how stale the air becomes. (That's why in Silicon Valley large companies have "air consultants" measure the freshness twice per year and report the rate. I've talked to some.) So my question stands on how and what to do to have more effective air circulation indoors, and what else we should do. And why is this conversation only happening several months into a lockdown. It's as if American government is falling down from learned helplessness.
smarx007 6y ago
Thankfully you missed that the article discusses history from 1956 regarding the airborne transmission study methodology. Otherwise you might have gotten a heart attack. Goodness!
Zenst 6y ago
I was thinking HEPA filtration may already cater for virus's, but with HEPA certification being .3 microns and the COVID-19 virus 0.12 microns, then it gets down to individual air conditioning systems. Some may use ionising in combination or UV. So I foresee a whole raft of legislation and requirements for office spaces ahead. Which will only help drive the work from home long-term as cheaper office space. But also help shift us away from open plan offices that I've never met anybody who liked. As for herd immunity - that really is best effective against viruses that do not mutate that quickly. Corona-viruses from my understanding, do mutate. Though it is often the case that mutations of a virus over time lean towards mutations that make them less impacting upon the host. Which may be down to natural selection in that those with no impact can spread it more and no virus really wants to kill the host. Impacted/dead hosts tend to be less effective in transmission. So may very well be down to that aspect in why they tend to become less impacting. On the UV aspect https://www.nature.com/articles/s41598-020-67211-2 https://www.nature.com/articles/s41598-020-67211-2 a UV wavelength of 222nm that is effective against the virus and safe for humans. Though how stable current UV output is and by that if you had a 222nm light, over time would that drift and become less human safe is something I'd want to check. There again - flu's and colds are more prevalent during winter months when we have less sun and less UV. Can't ignore that pattern.
- nradov 6y ago
  All viruses mutate, but so far SARS-CoV-2 has been mutating relatively slowly. It has an error correction mechanism which blocks the majority of mutations. By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year. The human species already has a significant level of herd immunity against four other endemic coronaviruses. The same thing will eventually happen with SARS-CoV-2 one way or another, but hopefully we will have an effective vaccine soon enough to accelerate that process while minimizing the death toll.
  - beagle3 6y ago
    > By contrast influenza lacks that error correction and mutates much faster, which is why we need a reformulated vaccine every year. That's true, but that might change soon (the "every year", not the mutation speed): Results of [0] are supposed to be published this quarter. I am hopeful for them to be positive. [0] https://www.biondvax.com/2020/07/last-of-12400-participants-completes-final-visit-in-biondvaxs-m-001-universal-flu-vaccine-pivotal-phase-3-clinical-trial/ https://www.biondvax.com/2020/07/last-of-12400-participants-...
krimeo 6y ago
And remember all that "all scientists say masks dont work, why are you wearing a face mask, are you stupid?" only to change to the exact opposite in may/june ?
- mieses 6y ago
  They started wearing masks which reduced their blood oxygenation and made them even stupider.

sharpercoder 6y ago

Can ultra-high resolution, ultra-high framerate and ultra-high zoom camera's measure exhalation of virii particles out of a humans mouth?

pvg 6y ago
Most viruses are smaller than visible light wavelengths. The biggest are about a wavelength or two. Edit: some sizes here, including SARS-CoV-2 https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-Compared-to-Other-Things.aspx https://www.news-medical.net/health/The-Size-of-SARS-CoV-2-C...
praptak 6y ago
Resolution of plain optics only goes up to the diffraction limit, which is not enough to see a virus. Then there are super-resolution techniques which can go beyond that, but I don't think any of them could be adapted to scan the vicinity of the coughing human in real time.
fulafel 6y ago
The virus is quite small and would have to be in some unconventional state to show up optically (could make an interesting what-if xkcd).

calibas 6y ago

It seems the reasoning by officials is, "Yes, it's airborne, but there's not enough N95 masks for everyone so we don't want to cause panic or an N95 mask shortage for doctors and nurses by admitting it's airborne."

dboreham 6y ago
Also supposedly if a disease is declared airborne then hospitals have to adopt various isolation measures beyond just N95 that are very costly. This may be the reason the powers that be won't announce airborne transmission until after the pandemic is over.
- shalmanese 6y ago
  We make fun of medieval medicine but look at this shit! We're pretending that saying some magic words has an effect on a physical reality of disease spread! Who says that saying its airborne "has" to mean that certain procedures have to be adopted? That's not a rule of the universe, it's a rule that humans came up with and agreed upon and humans have the power to fix. We distilled down a set of physical principles into a set of guidelines, forgot the underlying physical principles and now operate purely in the world of the manmade guidelines, totally oblivious to when the guidelines are no longer reflecting the physical reality.
  - sokoloff 6y ago
    Unless you say something like “look it’s airborne but that fact shall not be admissible into any future lawsuits on any topic” (and have certainty that that will stand up to review), I’m not sure you can fully equate to the current “it’s not been declared to be airborne transmissible.”
  - jchw 6y ago
    While I understand the frustration, the reality is we shouldn’t be making fun of either. Just because the end result of something is inarguably “stupid” does not mean that any of the things that went into it are “stupid.” To do the Hacker News thing and make a bad analogy to computer science topics in a totally irrelevant thread, this is how I view a lot of stuff people complain about these days (think JavaScript, or Electron apps.) Real life is hard. To be a bit more concrete, consider the following: if you have a system where people are not encouraged to follow the rules as written, they will work against the spirit of what is written as well as what is actually written. If you have a system where people are discouraged from not following the rules, they may still engage in things that do not follow the spirit or written rules, but there is some accountability. But you can also try to work around what’s written to follow the intent as well, and I think that is where you get weird, counterintuitive, “stupid” results that can still “make sense” (as opposed to clearly corrupt cases where it is “stupid” and also does not make sense.) I think people, especially literal minded as many here are, prefer concrete rules. But the knock-on effect is that its not easy to simply proclaim they’re made up any time it’s inconvenient, and it really shouldn’t be. Perhaps, in fact in my opinion, definitely, the “escape hatches“ for when rules don’t work out practically are broken, but I still do prefer having rigid standards, especially for health. Hopefully, although it is probably not going to happen, organizations can have some postmortem-style reflections on what went wrong, so that hopefully next time we can be better prepared. History loves repeating though, so, you know.

lucb1e 6y ago

TL;DR: the actual experiment: > they constructed an air-tight closed ventilation system that connected a six-room tuberculosis ward to an exposure chamber with 150 guinea pigs. (Among rodent animal models, only guinea pigs could cough and sneeze, making them ideal for studying how respiratory diseases spread.) The guinea pigs were exposed to the infected air over a four-year period. A second group of 150 guinea pigs acted as controls: their air ducts were irradiated with UV-C lamps to kill TB bacilli. Results: > an average of three guinea pigs per month contracted TB, while no controls were infected. The experiment [also] quantified how many TB infections could be expected to result from exposure to a given number of patients over a defined interval. Relevance to COVID-19: > Riley’s research points to wearing masks and disinfecting air in enclosed spaces as two of the most effective tools for fighting COVID-19

nostromo 6y ago
Today I learned: > The animals were used so frequently as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject. https://en.wikipedia.org/wiki/Guinea_pig https://en.wikipedia.org/wiki/Guinea_pig
- ISL 6y ago
  In the same spirit, I offer Tami Knight's Avalanche Poodle: https://www.snowmediazone.com/the_zone/data/500/medium/Avi_poodle.jpg https://www.snowmediazone.com/the_zone/data/500/medium/Avi_p... Among my friends, to go first in an uncertain situation is sometimes called, "poodling it".
- dehrmann 6y ago
  Same for lab rats.
contravariant 6y ago
Some things worth pointing out about the linked article (not by Riley), regarding masks and disinfecting air: https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.096214 https://ajph.aphapublications.org/doi/10.2105/AJPH.2006.0962... - It contains no experimental data, it's a review of possible methods. - It's not about Covid-19, although that's to be expected. - The masks it talks about are N95 and N100 respirators (which it notes aren't in adequate supply). Some interesting quotes: > If one assumes that influenza is transmitted by respiratory droplets [..] rather than by aerosols [..], the supposition may be that keeping a safe distance may obviate the need for a mask. It is stated that the range of such droplets is generally no more than 3 ft. We are unable to locate the basic science behind that assertion. > Whether contagious as a respiratory droplet, aerosol, or both, there have been no controlled studies to investigate the efficacy of respirators in preventing the transmission of influenza A > there is a theoretical problem in the logic underlying N–95 respirators. Assume an N–95 mask functions better than its rating and at a sedentary inhalation rate blocks 98% of the bioaerosols that it is confronted with. We are still left with the 2% that penetrate through the filter, to be inhaled by the wearer. Whether discussing tuberculosis, influenza, measles, or smallpox, we do not know the concentration of pathogenic bioaerosols in the environment, nor do we know the minimum infectious dose for these pathogens. Anyway I don't think anyone disagrees with their conclusion that having everyone wear N100 masks is a good idea, but I'm not sure if any of their proposed methods are feasible. And the most important conclusion of their research is perhaps that we know way too little about possible countermeasures.

trhway 6y ago

> ultraviolet-C disinfection technology for air purification systems that were installed in health care facilities, factories, and NASA space capsules. Today, this technology is being used in Shanghai, Moscow, and New York City to protect subway and bus passengers against SARS-CoV-2, and China is also using the technology to disinfect hospitals Russian FSB has just arrested (on secret state security charges) on his short trip back home from China a top high voltage systems specialist who has been working for the last two decades on UV water and air cleaning system in South Korea and China. Seems it is becoming a sought after hot tech in the current situation.

thaumasiotes 6y ago
Any kind of air cleaning is relevant, and in demand, in China. Unfortunately, air purifiers have embraced the situation by demanding luxury pricing.

lifeisstillgood 6y ago

UV-C lights that irradiate an air duct is literally the most surprising (and in retrospect obvious) thing I learnt today. Is this something a household HVAC could be upgraded to. Do HNers in areas that have air con think it's a "yeah people will want that" idea?

TheSpiceIsLife 6y ago
What magnitude of irradiance is required? If the required power is,say, 500w continues, or more, that's going to get quite expensive to run. For example, where I live running a 500w device 24/7 is going to add an extra $1100 a year to the power bill.
- tzs 6y ago
  Looking at germicidal bulbs at 1000bulbs.com, the highest wattage bulb they have is 65 watts [1]. Most are well under that. Looking at random in-duct systems, it looks like they range from 1 to 10 or so bulbs with the later being for commercial buildings. Home systems seem to lean toward 1 or 2 bulbs of maybe 20ish watts or so total. This site [2] says typically $15-30 per year energy cost [1] https://www.1000bulbs.com/product/113917/AU-LG64T5L.html https://www.1000bulbs.com/product/113917/AU-LG64T5L.html [2] https://www.pickhvac.com/faq/hvac-uv-lights/ https://www.pickhvac.com/faq/hvac-uv-lights/
ajsnigrutin 6y ago
I always wondered just how much UV-C do you need to effectively kill the virus (power vs duct diameter and air speed).... because, instead of traditional masks, you could take a small fan, blow air into a pipe with a UV-C bulb inside, and pump the sterilized air to the human... basically something like this: https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop https://www.youtube.com/watch?v=fzGrh2io9Ds&app=desktop
- Gibbon1 6y ago
  I tried looking into that this spring. I suspect the answer is for this virus not much. Nothing to indicate that any part of it's life cycle involves hanging around latent. Interesting bit on how UV-C works to sterilize. https://en.wikipedia.org/wiki/Pyrimidine_dimer https://en.wikipedia.org/wiki/Pyrimidine_dimer Interesting thing bacteria and some viruses have DNA repair enzymes that can fix damage from UV-C. Medically you're always bedeviled by bacterial and fungal spoors. Limitations with UV-C sterilization I think prevents wider use. Not a magic bullet. Though it probably works well for influenza, colds, and this bat virus.

ajb 6y ago

Ok, dumb idea time: suppose that everyone in an office sits on a chair that raises their body to X volts. At the same time a collector mesh is provided at each desk, at -X volts, but shielded so that you can't touch it and shock yourself. What X is large enough to ensure that all the virus particles you cough out end up at the collector? Is it possible to do this without electrocuting everyone?

deleted 6y ago
[deleted]
vimax 6y ago
that sounds kind of like what an ionized air purifier does
imposterr 6y ago
Free electrons tend to distribute themselves on an object as to minimize the repulsive forces between them. This usually means that they distribute evenly on the surface of objects. Humans are a bit more complicated in structure than say a metal ball, but my guess would be that there would be a similar situation where all the free electrons would just build up on the skin. Therefore, I don't think the particles one would cough up would be negatively charged.
- enchiridion 6y ago
  Would the particles get charged as they pass through the later of electrons?
- curryst 6y ago
  Alveoli are basically small air sacs in your lungs, so they're a surface (it's just an inverted ball, a hollow sphere in a not-so-solid object). No idea how that influences where the electrons go. I wonder how the nervous system would interact with that as synapses fire. I'm curious if they would build up, or if the synapses all over the body firing would make them bounce around constantly.
  - 6y ago

praveen9920 6y ago

Can we "mutate" a virus to use radioactive isotope of carbon (c-14? something that is not harmful for humans) so that we can observe how viral a virus is? Not an expert on radio isotopes or spectrography or viruses. Note: I know, radioactive virus at this point might freakout people a little.

koeng 6y ago
AFAIK there aren’t methods to do that in vivo, unfortunately.
ISL 6y ago
No need. It mutates itself. The propagation of genetic strains of Covid-19 can be viewed here: https://nextstrain.org/ncov/global https://nextstrain.org/ncov/global Our ability to do this for every single Covid-19 case in the universe is, I imagine, limited only by funding/infrastructure/training.
globular-toast 6y ago
Where would it get the carbon-14 from? Virus particles (virions) are made by and from their host. So you'd need a human made from carbon-14 first.
Jabbles 6y ago
We basically already know how viral viruses are because they undergo mutations, and we can trace which strain people have and where they caught it from by sequencing their DNA (technically RNA) and looking for the virus's "ancestors". See for example https://www.eurekalert.org/pub_releases/2020-10/du-gt100120.php https://www.eurekalert.org/pub_releases/2020-10/du-gt100120.... Also you wouldn't mutate a virus with C14 or similar radiactive isotope, because that can't be encoded in its genetics, and such a virus would use any old Carbon atom (most likely normal C12) to replicate. Finally, mutating a virus and releasing it seems ethically dubious in the middle of a pandemic...

lootsauce 6y ago

Ok dumb question why don’t we settle the question by conducting the experiment for covid19?

hurrynot 6y ago
The article says the TB experiment ran for four years. It isn't clear that you need four years to prove airborne transmission, but it is likely that you need a lot of time.
RogerKamben 6y ago
It's pretty much settled also for sars-cov2. A study in China found the virus in air samples taken inside the central air-condition system, far away from any patients (see bottom). Another found correlation between infected and where they were sitting vs AC duct outlets. Also the fact that mandatory masks have had zero effect on the R value in any country, same as for influenza and other "flu" viruses. If it was spread by droplets/surfaces then masks should at least have some effect to slow or contain the spread, like make a dent in the curves. Yes there are masks that prevent TB transmission but this bacteria is more than 10x larger than typical respiratory viruses. They look like duck beaks, are very uncomfortable and require training to use properly. I haven't seen these anywhere during this pandemic and they wouldn't help either as they are designed to prevent aerosols down to about 2um size. There is plenty of space for ~0.1um viruses even in 0.5um droplets. Some researchers even claim the virus can stay potent a while after the droplet evaporates and float around like dust. CDC meta study showing medical masks had no effect neither as PPE or source control: https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article Study comparing medical masks and N95 masks found no difference in transmission of influenza: https://pubmed.ncbi.nlm.nih.gov/31479137/ https://pubmed.ncbi.nlm.nih.gov/31479137/ More links and summaries collected here: https://swprs.org/face-masks-evidence/ https://swprs.org/face-masks-evidence/ This Time article has lots of links and info (but the argument for masks is complete fail): https://time.com/5883081/covid-19-transmitted-aerosols/ https://time.com/5883081/covid-19-transmitted-aerosols/ It's funny how some claim we didn't need masks before, but now we need them since it's spread by aerosols?? The truth is in fact the opposite and don't get me started on cloth masks...it's absurd. This seems more like covering their asses than following the science. Most of these studies involve health personell, with high-end masks, the general public will of course do much much worse. This survey of studies and history of mask use in dentistry is also informative (why was it taken down?): https://archive.is/My2jr https://archive.is/My2jr The WHO reversal on mask use is also revealing: On July 12, Deborah Cohen, the medical correspondent of BBC2’s Newsnight, revealed on Twitter that: ‘We had been told by various sources [that the] WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying.’ She said the BBC had then put this to the WHO, which did not deny it. In March, the WHO had said: ‘There is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can protect them from infection with respiratory viruses, including Covid-19.’ -Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564-7. -Fears AC, Klimstra WB, Duprex P, Weaver SC, Plante JA, Aguilar PV, et al. Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions. Emerg Infect Dis 2020;26(9). -Chia PY, for the Singapore Novel Coronavirus Outbreak Research T, Coleman KK, Tan YK, Ong SWX, Gum M, et al. Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients. Nat Comm. 2020;11(1). -Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020. Emerg Infect Dis. 2020;26(7). -Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center (pre-print). MedRxiv. 2020 doi: 10.1101/2020.03.23.20039446. -Zhou J, Otter J, Price JR, Cimpeanu C, Garcia DM, Kinross J, et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.24.20110346. -Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature. 2020;582:557-60. -Ma J, Qi X, Chen H, Li X, Zhan Z, Wang H, et al. Exhaled breath is a significant source of SARS-CoV-2 emission (pre-print). MedRxiv. 2020 doi: 10.1101/2020.05.31.20115154. -https://pubmed.ncbi.nlm.nih.gov/19797474/ https://pubmed.ncbi.nlm.nih.gov/19797474/ -https://pubmed.ncbi.nlm.nih.gov/19216002/ https://pubmed.ncbi.nlm.nih.gov/19216002/

dmix 6y ago

This quote from the report should be top of the list of the lesson-learned from this COVID pandemic: > The current guidance from numerous international and national bodies focuses on hand washing, maintaining social distancing, and droplet precautions. Most public health organizations, including the World Health Organization (WHO) [16], do not recognize airborne transmission except for aerosol-generating procedures performed in healthcare settings. Hand washing and social distancing are appropriate but, in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people. This problem is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation [17] relative to the number of occupants and extended exposure periods (as graphically depicted in Figure 1). For example, airborne transmission appears to be the only plausible explanation for several superspreading events investigated that occurred under such conditions [10], and others where recommended precautions related to direct droplet transmissions were followed. Indoor contact, proper veneration, etc causing super-spreader events. Meanwhile here in Canada they waited until late May to even recommend wearing a mask in such situations (other countries like the US had similar time frames and Dr Fauci openly admitted they withheld this recommendation for the benefit of healthcare workers). https://www.ctvnews.ca/politics/it-s-now-recommended-that-canadians-wear-face-masks-1.4946752 https://www.ctvnews.ca/politics/it-s-now-recommended-that-ca... Much like drug prohibition and other grand social control experiments, I'm not convinced the value of being vague or simply straight up not recommending masks in order to keep supply chain available for healthcare workers was ultimately worth the downside. If supply chains was the issue then spend the government law enforcement power controlling and directing the supply chain for medical quality masks. This 4 month experiment (and I'm being generous there) where Feb, Mar, Apr and most of May they spent creating confusion and not recommending masks ultimately did more harm than good. Now pundits and online commenters love to attack these anti-mask people when for much of the year expert sources were far from making masks the recommended choice. Including gov-delivered misinformation about their utility in order to explain themselves. If the pro-social control (ie, lying the public) group thinks it was really stopping the wealthy and connected from completely ignoring these guidelines, then they are lying to themselves. As always with these gov poppet-mastery policies the only losers were the lowest common denominator poor people. Plenty of which still don't funny trust masks. I would have rather spent four+ months explaining the virtues of masks and explaining the supply problem honestly. Than playing catch up last minute. The fact Asia who had adopted masks, and never spent any time lying or dodging their public on their utility, have done better than western countries is no surprise. Asian countries had masks well before COVID. The older I get the more cynical I become about government and intelligentsia 'we know whats best', that includes withholding information (something extra popular in healthcare). All information should be as transparent as possible, regardless of fantasies of controlling it.

tech6 6y ago

I have an ozone vegetable washer. Is it dangerous to be in same room when this vegetable washer is running ? I can smell the odour of ozone near the vegetable washer

ficklepickle 6y ago
The odour detection threshold is 0.005-0.02 PPM. OSHA says less than 0.1 PPM over an 8-hour period. So you can smell ozone well before it is in the harmful range. Some air circulation wouldn't hurt while the device operates, but napkin math says you are OK.

pbreit 6y ago

Was there any doubt?

globular-toast 6y ago
Yes. A very quick, less than a minute, skim of the article would tell you that.

pa7x1 6y ago

The idea of respiratory viruses not being airborne sounds silly. What's the viral charge supposed to do, not jump into droplets smaller than certain size? Of course they are present in the smallest droplets! They are present in the mucous secretions of the infected individual and they will get expelled through the big and the small droplets. The distinction shouldn't be a qualitative one, airborne vs not airborne. It's a quantitative one, sufficiently infectious viruses may pose a risk at much smaller doses, the kind that you may be exposed by the smallest droplets expelled that simply stay afloat. It's also worth noting that human immune response is a complicated beast, what may not be infectious for an average healthy individual may put down someone with a weakened immune response. So even supposedly "not airborne" viruses that are very unlikely to infect the average healthy individual at very small doses may pose an "airborne" risk for individuals with a weakened immune response. There are more factors in all of this, atmospheric conditions may play a role. For example, cold temperatures may be more suitable for the virus to remain infectious outside of a host, thus increasing the likelihood of "airborne" propagation. TL;DR: The distinction between airborne and not airborne viruses is an artificial one. That only makes sense statistically for an average individual at certain atmospheric conditions for a concrete strain of the virus. But as any real-world statistical distribution there are tails and you will find "airborne" qualities for pretty much any respiratory virus in those tails.

temptemptemp111 6y ago

Bogus "experiment" - happy to debate anyone on the topic, but I'm sure they'll just censor my proof.