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Thread: Disease and pandemics thread (because it's science)

  1. #2101
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    There is now a lot of data emerging that makes it more possible to calculate the fraction of people who get the disease who die from it. All you need is serological testing of a subpopulation, and compare that to deaths from that subpopulation, something that is very easy to do. Ideally, we would have random serological testing of a wide array of subpopulations (by age, by career, by nation, etc.), so we can get the death probability for all these groups. One can only assume that data will eventually become available, because it is so easy to do and so obviously crucial. What we do have at present is a number of nations reporting serological results used to gauge their current herd immunity, and we can easily compare that to the reported deaths from that country. The purpose is to see if there are consistent numbers emerging to gauge the death probability, which in turn informs whether or not it is advisable to shoot for herd immunity via infection, vs. via vaccination. Here is an article (https://www.cnn.com/2020/05/21/healt...ntl/index.html) that reports these serological results: Sweden, 7.3% infection, 3,871 deaths, population 10.2 million, death probability 0.5%. US, 5-15% infection, 96,000 deaths, population 330 million, death probability 0.2 - 0.6 %. So the numbers are still rough, and it's never clear if the serological tests are truly randomly sampled from the same population that the deaths come from, but a consistent picture is beginning to emerge that the overall death probability across the entire population is something like 0.4 or 0.5% on average for every person infected. Obviously it is much higher for those in high risk groups.

    This is a crucial statistic, because it means that to achieve 70% herd immunity via infection, one must tolerate the death of about 0.3% of one's entire population. That immediately means that if a nation does not want 0.3% of its population to die, they must slow the infection rate until vaccines are achieved. This is if the infected fraction is global to the whole population, ideally those most vulnerable could have a lower infected fraction but then again we are finding that even young people can have bad complications and can lead to death. 0.3% of the US population is a million people, or not much less than died in the 1918 Spanish flu epidemic (which achieved herd immunity via infection). The current death toll in the US is about 10,000 per week, and much of the country is talking about opening up, so if the death toll does not go below that mark, a million deaths would take about two years. If the death toll returns to its peak rate of 20,000 per week, it would only take one year, or comparable to estimates for achieving a vaccine (also highly unknown). In other words, if the death rate is allowed to return to its prior peak, a million will likely die in the US, and there will be little point of having a vaccine once it is obtained. If the death rate is maintained at what it is now, a vaccine in a year would save half a million lives, but a half a million will have died by then. These are conclusions that require no analysis or opinion, they are just facts and arithmetic. The additional number of people that suffer reduced standard of living, yet survive, is unknown and not counted in these statistics.
    Last edited by Ken G; 2020-May-22 at 01:02 AM.

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    Additional information is emerging about how the disease spreads. Although it was claimed early in the virus that the primary mode of transmission was by contacting infected surfaces, suggesting that constant hand-washing should be suitably protective, the latest word from the CDC (https://www.usatoday.com/story/news/...es/5235317002/) tells us "Though there is the possibility that coronavirus could be transmitted by touching a surface — and then your nose, mouth or eyes — the likelihood of that is lower than person-to-person contact, which is believed to be the primary way coronavirus is transmitted." Typically, "person to person" means either airborne aerosols, or droplets flying about 6 feet during interactions. It is currently thought that COVID-19 spreads in droplets up to about 6 feet, hence social distancing, but how well it can be aerosolized by yelling (say in sports crowds) or singing (as in that choir that got sick at distances more than 6 feet) remains unclear. We do know that the guidance on masks has changed from early advice to only wear masks (even cloth masks, not widely needed by healthcare workers because they are not protective against aerosols) if you have active symptoms, to the recent "In light of this new evidence, CDC recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies),' i.e., everyone, not just those with symptoms. So I think the mask debate is finally resolved, as new evidence has come forward-- surfaces are not the main enemy, the air is. Of course we should still wash hands, because it's easy, and we should wear cloth masks, because that's easy too. Staying out of crowds in contained spaces or with poor ventilation seems the best of all.

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    Quote Originally Posted by Ken G View Post
    Additional information is emerging about how the disease spreads. Although it was claimed early in the virus that the primary mode of transmission was by contacting infected surfaces, suggesting that constant hand-washing should be suitably protective, the latest word from the CDC (https://www.usatoday.com/story/news/...es/5235317002/) tells us "Though there is the possibility that coronavirus could be transmitted by touching a surface ó and then your nose, mouth or eyes ó the likelihood of that is lower than person-to-person contact, which is believed to be the primary way coronavirus is transmitted."
    Was it really claimed at one point that the primary method of transmission was by touching surfaces? I donít recall that, but am honestly not sure. I had just thought that person-to-person was primary, surface contact secondary, especially depending on how fresh the contact was. For instance, I wasnít nearly as concerned about touching my mailbox or mail hours after other contact than something handled seconds or minutes prior.

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    Quote Originally Posted by Van Rijn View Post
    Was it really claimed at one point that the primary method of transmission was by touching surfaces?
    I'd be amazed if any reputable source ever made that claim. It's all a continuum--the virus sits in secretions, and you can end up with those secretions on or in your own body by various routes. Both routes of infection for respiratory diseases have been acknowledged for many decades, though there are difference between viruses about how well they survive on surfaces or in drying droplet nuclei. So the advice from the outset has been, and still is, to mitigate both routes--hand-washing and social distancing being the core demonstrated effective endeavours in these two modalities.

    And responding to another point in the same post of Ken G's, I'd point out that the "mask debate" isn't remotely "resolved". The data are still poor quality and heterogeneous, and people are still reading it and coming to either various very soft conclusions, or diametrically opposed hard conclusions. What has resolving is the public health authorities' attitude to masks, based on those inadequate data, and that varies from country to country. Authorities have effectively been bounced into taking a stance on mask use because citizens have demanded advice. But both stances employ a precautionary principle--either you adopt the stance that the evidence for benefit is poor, but masks will likely do no harm; or you say that the evidence for benefit is poor, and masks have the potential for harm.

    So if you are planning on wearing a mask, please take a look at the WHO guidance on safe use. (If you're reusing a cloth mask, you need to launder it after each use.) The main thing is to think of the mask surface, inside and out, as being radioactive once it's in use--you just never touch it again, and never lay it down on a surface someone else might use. (Even a brief glance at the television these days reveals that most face-mask wearers have absolutely no idea how to use a face mask properly.)

    Grant Hutchison

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    Quote Originally Posted by Van Rijn View Post
    Was it really claimed at one point that the primary method of transmission was by touching surfaces?
    Had I just been getting my advice from the UK's main news providers I would have concluded that transmission was by contact only. I knew better, but I did have to check.

    Mark
    Last edited by holmes4; 2020-May-22 at 05:29 PM.

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    Quote Originally Posted by holmes4 View Post
    Had I just been getting my advice from the UK's main news providers I would have concluded that transmission was by contact only.
    You've got to wonder what these journalists thought the whole "two-metre separation" thing was for. Did they really imagine it was to prevent people inadvertently touching fingertips at full stretch?

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    Good to see that various journalists in the UK are taking the time to talk to experts about the ineffectiveness of wearing a paper surgical face mask in public places. It's not going to change your chance of contracting coronavirus, unless:
    a) Someone walks up and coughs in your face
    b) It helps to remind you not to touch your face with your hands (which is no substitute for washing your hands)

    Nor will it change the chance of your transmitting coronavirus to someone else, unless you're planning to walk up and cough in their face.

    Buying and hoarding these things just makes them less available for situations where they are actually functional and useful.

    Grant Hutchison
    What kind of mask are we supposed to use?
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    Quote Originally Posted by Copernicus View Post
    What kind of mask are we supposed to use?
    I presume whatever is required by the administration where you live. There are other things apart from science involved in those decisions, and I have no intention of getting into that here. I suppose we should just be glad that people aren't being shot in the street for non-compliance yet, as happened in 1918.
    The main issue, as I said above, is that if you or your government decides that you should wear a face covering, you really need to know how to don, doff and handle it safely. Instructions are available, like the WHO poster I linked to earlier. I'm sure you're fine at all that, but lots of people quite evidently have no clue. Improvised cloth coverings appear to be particularly problematic, from what I've seen on television of people in the USA using them, and if I were ever required to wear one I'd certainly have multiple practice sessions in my own home before I went out.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    If you're reusing a cloth mask, you need to launder it after each use.
    Even if youíre using it for a short period no more than once per two week interval? Basically, I see mask wearing as a nearly pointless ritual to make some nervous people feel better on the rare occasions during the CU when I actually am breathing air at the same location as another human. The event is unlikely to last more than a short period until the mask is placed back in storage.

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    Quote Originally Posted by grant hutchison View Post
    I'm sure you're fine at all that, but lots of people quite evidently have no clue. Improvised cloth coverings appear to be particularly problematic, from what I've seen on television of people in the USA using them, and if I were ever required to wear one I'd certainly have multiple practice sessions in my own home before I went out.

    Grant Hutchison
    I especially like the ones worn below the nose. Almost as good are the extremely loosely fitted ones that barely do more than mildly affect the direction breath may go. My response, of course, would be to make a point of keeping my distance.
    Last edited by Van Rijn; 2020-May-22 at 11:02 PM.

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    Quote Originally Posted by Van Rijn View Post
    Even if you’re using it for a short period no more than once per two week interval?
    Well, no reason not to wash it, if that's your frequency of usage. Viruses may not last that long, but if it's damp with breath and liberally salted with skin cells and bacteria from your skin and nose, I wouldn't want to let it brew for a couple of weeks and then reapply it. Yech.

    Grant Hutchison

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    Quote Originally Posted by Van Rijn View Post
    Was it really claimed at one point that the primary method of transmission was by touching surfaces?
    Only everywhere, over and over. I literally could not count the number of times I heard "the virus spreads by the hands touching the nose or the eyes." I even commented on this much earlier in the thread, where I was wondering why no one ever mentioned touching the mouth. But of course, the real oversight was not mentioning droplets passing through the air and landing in the eyes, nose, or mouth, which is now being called the primary mode of infection in a number of sources. That's what "person-to-person" means, i.e., no intervening surface, when we are not talking about sharing needles or sexual transmission. I suppose "shaking hands" could be regarded as a kind of hybrid case of person-to-person and surface-related transmission, but I doubt handshaking is any important vector for COVID-19 at this point.

    There's also the issue of viral load, which we don't hear much about because it's hard enough to track infection of any type. It certainly seems possible to me that someone might get a very low exposure, perhaps via some surface, which then incubates the virus in their body-- but only enough to make them contagious to others, not enough to pose a threat to the person. The person might be asymptomatic or presymptomatic and ultimately get only mild symptoms, but they may still make droplets with a significant viral load, that could kill someone else by giving them a much more serious viral load via the person-to-person route. The potential advantages of mask wearing in that scenario may be one of the primary motivators of the new guidance, now that we understand how prevalent is asymptomatic transmission.

    I had just thought that person-to-person was primary, surface contact secondary, especially depending on how fresh the contact was. For instance, I wasn’t nearly as concerned about touching my mailbox or mail hours after other contact than something handled seconds or minutes prior.
    You just described a surface contact, which isn't surprising given how programmed to think that you have been up until now. Hence all the emphasis on hand-washing, which is no longer regarded as a sufficient safety measure. Ergo the new recommendations on mask usage, as much to limit your own projection of droplets while you are asymptomatic as to limit your receiving such droplets. Certainly if someone coughs in my face, I'm glad I'm wearing a mask, but I'm taking that mask off right away and I'm still quite concerned.
    Last edited by Ken G; 2020-May-23 at 06:56 PM.

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    Quote Originally Posted by grant hutchison View Post
    And responding to another point in the same post of Ken G's, I'd point out that the "mask debate" isn't remotely "resolved".
    That actually depends on what the words were intended to mean. When I said the debate is resolved, I did not mean we now know every facet of how COVID-19 is primarily transmitted, I'm sure there is still a lot to learn about this disease. What I meant was that it is resolved that we should wear cloth masks in public. I think that is indeed quite well resolved, and it is certainly the current guidance of the CDC. Here is a recent article on the topic: https://www.preprints.org/manuscript/202004.0203/v2. It's a preprint, but that's the best way to get up-to-the-minute information, it certainly seems authoritative given the author list.
    The data are still poor quality and heterogeneous, and people are still reading it and coming to either various very soft conclusions, or diametrically opposed hard conclusions.
    If by "people," you mean me, no, I am only the messenger here, this is the CDC guidance. That I already had this opinion before is of no consequence now.

    Authorities have effectively been bounced into taking a stance on mask use because citizens have demanded advice. But both stances employ a precautionary principle--either you adopt the stance that the evidence for benefit is poor, but masks will likely do no harm; or you say that the evidence for benefit is poor, and masks have the potential for harm.
    Yes, we must go on what we now think is true, because the disease requires response now.

    So if you are planning on wearing a mask...
    You mean, if I am planning on following the CDC guidance, rather than flouting it?
    ...please take a look at the WHO guidance on safe use. (If you're reusing a cloth mask, you need to launder it after each use.) The main thing is to think of the mask surface, inside and out, as being radioactive once it's in use--you just never touch it again, and never lay it down on a surface someone else might use. (Even a brief glance at the television these days reveals that most face-mask wearers have absolutely no idea how to use a face mask properly.)
    Of course this is a completely different issue, how to use masks properly rather than whether or not proper mask use can be a key element in defeating COVID-19. It is likely that proper mask use is what will be key, so that means we should promote proper mask use (as in your helpful citation), rather than that we should stick to the original (and now seen to be incorrect) stance that masks should categorically not be worn (recalling the infamous all-caps tweet of the US Surgeon General, in obvious contradiction to the extremely good results obtained in places like South Korea). As I said earlier in the thread, if mask wearing is spreading COVID-19, how can we understand how little COVID-19 is spreading in places where mask wearing is extremely prevalent?

    But more importantly, this issue you raise of proper mask use, is a very important one, now that mask wearing is being recommended. So I have some questions. We have heard a lot of conflicting information about how long the virus can live on surfaces. Why is it necessary to launder a cloth mask (or whatever can be done to an N95 mask), instead of just setting it down for a few days? Does the virus live longer inside a mask than on a hard surface?
    Last edited by Ken G; 2020-May-23 at 06:41 PM.

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    Quote Originally Posted by Ken G View Post
    That actually depends on what the words were intended to mean. When I said the debate is resolved, I did not mean we now know every facet of how COVID-19 is primarily transmitted, I'm sure there is still a lot to learn about this disease. What I meant was that it is resolved that we should wear cloth masks in public. I think that is indeed quite well resolved, and it is certainly the current guidance of the CDC. Here is a recent article on the topic: https://www.preprints.org/manuscript/202004.0203/v2. It's a preprint, but that's the best way to get up-to-the-minute information, it certainly seems authoritative given the author list.
    The author list actually rings a number of alarm bells. Why are there so many? Why are clinicians so underrepresented? There's also an indication that the paper has failed first peer review, or perhaps merely been bounced at an editorial level. Version 1 was submitted to PNAS, but now we have Version 2--it's generally a no-no to be revising preprints on-line while they're under consideration, so I deduce (though I may be wrong) that there have been issues of some sort with the PNAS submission. But mainly I'm suspicious of the authors' great certainty after they've reviewed so many individual papers that are full of caveats and caution.

    Quote Originally Posted by Ken G View Post
    If by "people," you mean me, no, I am only the messenger here, this is the CDC guidance. That I already had this opinion before is of no consequence now.
    No, I mean "people". People who have read this literature and reflected on it. The authors of your preprint also make this point:
    Two other preprint systematic reviews by Brainard (42) and (43) concluded against and for the use of face masks by the public respectively. This conflicting interpretation of the literature points to fundamental disagreements in what is considered to be best available evidence.
    My bold. Which is why I say this issue is still fundamentally unresolved at a scientific level, there being no consensus in reviews of the evidence.

    Quote Originally Posted by Ken G View Post
    You mean, if I am planning on following the CDC guidance, rather than flouting it?
    Puh-lease. There are lots of reasons for people to plan to wear masks, and lots of people live in countries where the CDC guidance does not apply, including countries where the official guidance is that there's no evidence to support mask use in public spaces.

    Quote Originally Posted by Ken G View Post
    Of course this is a completely different issue, how to use masks properly rather than whether or not proper mask use can be a key element in defeating COVID-19.
    Yes, it's a completely different issue. But it's about using a mask safely. If people decide to wear a mask, for whatever reason, then I think they should know how to do so without endangering themselves or others.

    Quote Originally Posted by Ken G View Post
    So I have some questions. We have heard a lot of conflicting information about how long the virus can live on surfaces. Why is it necessary to launder a cloth mask (or whatever can be done to an N95 mask), instead of just setting it down for a few days?
    Given your feeling that the science of mask usage has been resolved essentially by fiat from the CDC, then I 'll just point out that the CDC tells you to do it. Conversation over, surely?

    My own reason was given in response to Van Rijn:
    Quote Originally Posted by grant hutchison View Post
    Well, no reason not to wash it, if that's your frequency of usage. Viruses may not last that long, but if it's damp with breath and liberally salted with skin cells and bacteria from your skin and nose, I wouldn't want to let it brew for a couple of weeks and then reapply it. Yech.
    Grant Hutchison

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    Quote Originally Posted by Ken G View Post
    Only everywhere, over and over. I literally could not count the number of times I heard "the virus spreads by the hands touching the nose or the eyes." I even commented on this much earlier in the thread, where I was wondering why no one ever mentioned touching the mouth. But of course, the real oversight was not mentioning droplets passing through the air and landing in the eyes, nose, or mouth, which is now being called the primary mode of infection in a number of sources.
    I have to agree with Ken on this. At least in the US, it was all about washing your hands, avoidance of touching your face, and wiping-down frequently-touched surfaces. For quite a while, the mainstream advice was that masks do nothing for the general public. My inner CT wonders if that was done simply to avoid exacerbating the mask shortage for healthcare workers who desperately needed them.

    Currently, I can't enter my office without a mask. It may be a cloth mask, or an N95 mask, but must not have an exhaust valve. The idea is to contain my spittle to myself, and everyone else's to themselves as much as possible. Will it help? I don't know. We are still implementing work-from-home-when-possible, social distancing, when possible, and frequent disinfection of the office space surfaces.
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    Quote Originally Posted by Extravoice View Post
    I have to agree with Ken on this. At least in the US, it was all about washing your hands, avoidance of touching your face, and wiping-down frequently-touched surfaces. For quite a while, the mainstream advice was that masks do nothing for the general public.
    You had six-feet social distancing as part of your advice in the USA right at the start, though. It was being discussed by American members here as far back as early March, and it's still the primary measure the CDC recommends, even on its facemask page. That's because it's the main, proven intervention to protect against direct person-to-person transmission. So the advice was always, then as now, to minimize the two main methods of transmission--surface contamination and person-to-person. Really, no public health authority in the world would try to limit the spread of a respiratory disease without issuing advice on ways to limit direct respiratory spread. It's a shame if the relevance of the six-feet distance rule didn't get out to people clearly, but it was still there in the guidance. In fact I remember discussing its relevance here, early in the pandemic, perhaps even on this thread.

    Grant Hutchison
    Last edited by grant hutchison; 2020-May-23 at 09:10 PM.

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    I canít say the exact date, but yes social distancing was recommended sometime in March. Although it wasnít required, everyone on my office team attended our March 19 status meeting via Skype. By the next week, we were attending from home.

    That said, the general impression at the time was that you could get infected by being close to someone coughing, or might touch something someone had coughed on/nearby and you would pick up the particles that way. It was much later that the general consensus was that you could get directly infected from speech-released droplets.


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    Quote Originally Posted by grant hutchison View Post
    The author list actually rings a number of alarm bells.
    It is certainly crucial to understand the clinical evidence in favor of using masks, on which the CDC is basing their new guidance. That preprint was merely one example. Perhaps this is a better one: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7191274/ . It concludes "The study suggests that community mask use by well people could be beneficial, particularly for COVID-19, where transmission may be pre-symptomatic. The studies of masks as source control also suggest a benefit, and may be important during the COVID-19 pandemic in universal community face mask use as well as in health care settings."
    So yes, those words are couched in uncertainty, but as I said, the "resolution" is not about what we know about COVID-19, it's what we know about what seems to be the right response to the new data. We will always be forced to take action based on uncertain knowledge, because by the time scientific certainty arrives, the epidemic may be almost over-- a point you have made yourself. These papers represent the best information we have now, though of course any individual scientist is welcome to say "I'm not convinced." Nevertheless, the CDC and other health organizations must use their best logic to give guidance now, and that's what they are doing. The key new information appears to be how much asymptomatic transmission is occurring, on grounds that before they would have stressed the need for the symptomatic person to just stay home, but obviously that advice is not much good for asymptomatic people. So now they are saying, wear a mask, in case you are contagious. That's what they've been doing in South Korea from the start, and they had one or two people dying each day, at the same time the US had one or two thousand. Masks weren't the only difference, but how bad could they be.

    There are lots of reasons for people to plan to wear masks, and lots of people live in countries where the CDC guidance does not apply, including countries where the official guidance is that there's no evidence to support mask use in public spaces.
    So if the UK alters their guidance and promotes the use of public mask use, will you then regard the issue as resolved, or will you still think they are merely bowing to some form of public pressure? I predict it won't be long now before that happens, and for the same reason-- telling people to stay home if they have a fever is simply not going to cut it, as we now know.
    Yes, it's a completely different issue. But it's about using a mask safely. If people decide to wear a mask, for whatever reason, then I think they should know how to do so without endangering themselves or others.
    And of course I have no disagreement there, indeed that's what I'm saying-- we must start telling people how to use masks properly, and stop telling them not to wear masks.
    Given your feeling that the science of mask usage has been resolved essentially by fiat from the CDC, then I 'll just point out that the CDC tells you to do it.
    I'm not sure what you mean "by fiat," I personally never to listen to anything on that basis (remember, I agree with Feynman, I'm skeptical of the knowledge of experts). It is more this forum that relies on "fiat", hence the rules of this thread. Instead, I personally look at the reasoning, and here is the reasoning the CDC gives at https://www.cdc.gov/coronavirus/2019...coverings.html :
    "These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Studies and evidence on infection control report that these droplets usually travel around 6 feet (about two arms lengths)."
    So right there we have the entire basis for the "social distancing" concept, which is that the most dangerous mode for disease transmission is direct person-to-person, not indirect person-to-surface-to-person, the latter of which would not care about 6 feet (nor would the example Van Rijn just gave.) In that light, we see that the new guidance on mask wearing is consistent with the social distancing concept, because we are now less concerned about touching infected hands to our faces, and more concerned about inhaling droplets directly. We should not understress that the common language on this has just completely changed-- a month ago, all I ever heard is that I must wash my hands because I could be touching infected surfaces, but now all I hear is that surfaces are not really the main concern, direct contact with droplets flying through the air is now my concern. This is the new language I'm getting from all media outlets now, and it was quite an abrupt change (with very little mention that, oh by the way, this is totally different from what we were saying a month ago).
    My own reason was given in response to Van Rijn:
    So masks are only "radioactive" for a few days. That's what I expected, but it's nice to have it confirmed. My own approach is simply to have ten or so cloth masks, and cycle through them so I never wear the same one in less than three or four days. So this is quite easy, not any real problem, given how easy it is to obtain or even construct cloth masks. (We actually have a few N95s because there are immunocompromised people in my household, but we debate giving them over to the hospital. I'm not really hearing that N95s are that difficult to obtain in hospitals in my area at present, indeed authorities are bending over backward to stress what a great job they are doing to make sure all healthcare workers have plenty of PPEs.)
    Last edited by Ken G; 2020-May-24 at 12:18 AM.

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    Quote Originally Posted by Extravoice View Post
    That said, the general impression at the time was that you could get infected by being close to someone coughing, or might touch something someone had coughed on/nearby and you would pick up the particles that way. It was much later that the general consensus was that you could get directly infected from speech-released droplets.
    I don't think that's correct, though it may have been part of the context (along with asymptomatic spread) when the CDC was talking about reviewing its face-covering advice.
    This is a complicated issue (again). I'll list some bullet points, but am happy to elaborate if people want an in-depth defence.
    1) We've long understood that speech is part of a continuum with singing, shouting, sneezing and coughing in terms of shooting droplets into the environment. So that's not a new finding.
    2) Various activities produce various sizes of droplets, and that varies from person to person and event to event.
    3) There's a sort of false contrast invoked sometimes, between large droplets and aerosols--it's all a continuum, with big droplets falling out fast (therefore brief, short-range risk) and small droplets floating around over greater distances for greater times. There's a conventional cut-off at five microns, below which size these tiny droplets are said to contribute to "airborne" infection (that is, stuff floating in the air for long periods), whereas the larger stuff is "droplet spray" (stand back and you're fine). [Caution: the word "airborne" is sometimes applied to droplet spray as well--check context before interpreting.]
    4) Some viruses are very happy floating around in aerosols, while some seem to have a predilection for big droplets. So chickenpox, for instance, is very transmissible by the "airborne" route, whereas the common cold viruses (including coronaviruses) seem to prefer droplets. The differences can be detected epidemiologically, with airborne viruses tending to produce lots of secondary infections and therefore having an associated high R0 number.
    5) We have recent evidence that speech produces lots of little droplets that hang around (but no evidence they could carry an infective load of SARS-CoV-2); we have evidence of SARS-CoV-2 RNA being detected in the air around infected patients (but no evidence that this implies infective virions); and we also have conflicting evidence of no viral RNA in the air right in front of the mouths of other Covid patients. So that's all a bit murky.
    6) What we don't have, at present, is solid epidemiological evidence of SARS-CoV-2 being transmitted in the wild by the sort of airborne transmission we associate with these small speech droplets and viruses hanging in the air. There's big data from China, for instance, looking at the transmission rate within households (so no masks, enclosed space, people speaking), and the secondary infection rate is a better match for "common cold" droplet type transmission, rather than aerosol transmission. And the R0 of Covid-19, across multiple countries and settings, aligns better with the droplet-transmission model than the airborne model.
    7) What we do have are case studies. Unfortunately, they push in both directions--there's the choir apparently infected during singing practice; but there's the plane-load of long-haul passengers who remained uninfected by the Covid patient sitting in their midst.

    So it's all complicated and messy, as usual. For a brief glimpse of the lack of consensus on this one, take a look at the expert reaction to a recent paper dealing with the possibility of speech transmission in Covid-19.
    But public health authorities have to make decisions based on the data they have available. They put all the solid evidence-based stuff in place early--so hand-washing, disinfection, social distancing, all with proven track records in reducing R0 in respiratory diseases. Then they have to wade through a morass of conflicting, poorly designed, not-quite-applicable studies to try to tease out a useful signal to inform other decisions. Then someone just has to decide. But I think it's important in medicine to distinguish between definitive decisions ("this is what we should do") and definitive science ("here's why we're doing it"). In medicine, we often make definitive decisions based on incomplete, inadequate and downright unsatisfactory data, because that's all we've got, and we need to make some sort of decision right now. Another clinician, with the same data, might make a different decision.

    So when I point out where the science is uncertain, and where consensus is lacking, I don't disrespect decisions made by the CDC, any more than I disrespect the very different decisions made by Anders Tegnell in Sweden, or the decisions made in my own part of the world, which are different from both. Everyone had to make a decision, right now, and we'll only find out later what the advantages and disadvantages of those decisions were.

    Grant Hutchison

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    Quote Originally Posted by Ken G View Post
    Only everywhere, over and over. I literally could not count the number of times I heard "the virus spreads by the hands touching the nose or the eyes." I even commented on this much earlier in the thread, where I was wondering why no one ever mentioned touching the mouth. But of course, the real oversight was not mentioning droplets passing through the air and landing in the eyes, nose, or mouth, which is now being called the primary mode of infection in a number of sources.
    Quote Originally Posted by Extravoice View Post
    I have to agree with Ken on this. At least in the US, it was all about washing your hands, avoidance of touching your face, and wiping-down frequently-touched surfaces.
    I live in California and I watched and read the news. While hand washing has been heavily discussed, I never had the impression that doctors were claiming it was more important than social distancing. Wiping down surfaces was said to be important if there was a fair chance an infected person could have come in contact with them, with some information provided on how long viruses might survive.

    I donít ever recall a claim that the virus couldnít be spread by coughing or other typical person to person transmission. I donít ever recall a claim that transmission was restricted to touching the nose and eyes, only an emphasis on avoiding touching your face with unwashed hands because that made infection more likely. Washing hands was said to be important because it reduced the chances of infection, but I donít ever recall a claim that it was sufficient to stop infections on its own.

    I get the feeling you two heard arguments for doing things to make it less likely to be infected and took that to mean these were the only things necessary to avoid infection.

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    Quote Originally Posted by grant hutchison View Post
    Really, no public health authority in the world would try to limit the spread of a respiratory disease without issuing advice on ways to limit direct respiratory spread. It's a shame if the relevance of the six-feet distance rule didn't get out to people clearly, but it was still there in the guidance.
    I think you have missed not only how significantly the guidance has changed, but also the reason for the change. Early on, when we saw explosions of cases in nursing homes and on cruise ships, it was pretty clear to me that the virus had modes of spreading that were quite direct between people, and not about touching their faces and so on. So I was always surprised when I kept hearing that the main thing I had to do was wash my hands, and I'd be fine (I heard that many times, long before the concept of social distancing was even a common term, because the case numbers were still in the exponentially growing phase and people seemed to think that meant everything was basically OK in the US). I marveled at how a speeding train could be approaching and people basically said not to worry, it isn't here yet. But then the second shoe dropped, which was the growing awareness of how significant was the problem of asymptomatic transmission. Unfortunately, by the time we finally put these two pieces together, the US was leading the world in deaths, and lockdown was the only option.

    The significance of direct person-to-person transmission by asymptomatic people is what changed the guidance on mask wearing, not a relaxing of concerns that masks will be a source of infection. Masks were regarded as unnecessary, and there was a concern that symptomatic people would think it is OK to go out in public as long as they wore masks. There was also the concern that healthcare workers needed the good masks, which of course they do, so the issue was really about cloth masks. Finally, the prevailing idea was that masks that are not N95 aren't protective anyway, but this overlooked the role they could play in limiting the output of droplets (that came up long ago in this thread).

    But when you combine the general hesitance that Americans have to socially distance (and perhaps other places too, but here, I will simply state that nobody in public gives a hoot about social distancing), with lots of asymptomatic transmission through the air (and not on surfaces), it suddenly shifts the equation quite dramatically, and all of a sudden it seems to make a lot more sense to ask healthy people to wear masks. That is the logic behind the new guidance, and it represents a very significant shift in our model of how the disease mostly spreads. Early on, we thought you'd have people with fevers who were coughing all over the place, infecting surfaces right and left, and then some minutes or even hours later, unsuspecting victims happen by, touch the surfaces, and then touch their faces. Over and over I heard this model for transmission, and notice the clear strategy you use against it-- you require people who are obviously sick to avoid transportation and public spaces and quarantine at home, and you wash your hands like mad. But now we think it is transmitted more by asymptomatic people who have no idea they are contagious, and neither do the people around them, who are simply talking or breathing hard or singing, or maybe have an innocuous cough from allergies or a scratch in their throat, and people within 6 feet get directly hit by tiny droplets they are not even aware of, or inhale those droplets and get a significant viral load without suspecting a thing. Given that new model for how the disease is spreading, it is clear that the old guidance of staying home when you are clearly sick (which even then can be very hard to do for working people who live paycheck to paycheck, and certainly isn't going to happen to anyone who merely suspects they might possibly have been infected), and having everyone wash their hands a lot, is utterly inadequate. So the driving force behind the new guidance is the realization that something more has to be done, combined with the recognition that telling people to stay 6 feet apart at all times is simply not going to happen in the US (a fact that is quite obvious in any public space here, even though some efforts are being made and it's not a complete failure).

    Now of course this doesn't mean we shouldn't keep washing our hands, that's easy to do. It just means we should do other things that are also easy, like wearing cloth masks, and doing so with proper instructions. We need to do everything that's easy to do, that is being done with good results in the places that are getting good results, and that has not been either the US or the UK so far. So it's obvious we've missed something important, and we can hope it's cloth masks, rather than a simple unwillingness to social distance (because I think it will be easier to get people to wear masks than it will be to avoid groups).
    Last edited by Ken G; 2020-May-24 at 01:47 AM.

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    Quote Originally Posted by Van Rijn View Post
    I live in California and I watched and read the news. While hand washing has been heavily discussed, I never had the impression that doctors were claiming it was more important than social distancing.
    I don't think doctors said this, though the CDC has clearly shifted their focus from mostly person-to-person but sometimes from surfaces to almost entirely person to person and surfaces are much less of a concern. It was more how it got explained to people-- wash hands because surfaces are the danger. That's what you'd think if you expect contagious people to be symptomatic and easily isolated. I'm not sure the first time I even heard the term "social distancing", but I'm sure it was long after I heard the term "coronavirus pandemic." But anyway, I shouldn't stress the change in focus because it's backward-looking, what matters is forward-looking. The new guidance stresses the role of direct transmission of droplets from asymptomatic or presymptomatic people, and that is where the new focus on mask wearing is coming from. You'd have to ask them why they changed the guidance there, but we know it's not because of any new properties of cloth masks. Maybe they just started to pay attention to the places that are getting good results, but that's merely speculation.
    Last edited by Ken G; 2020-May-24 at 02:25 AM.

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    Quote Originally Posted by Ken G View Post
    So if the UK alters their guidance and promotes the use of public mask use, will you then regard the issue as resolved, or will you still think they are merely bowing to some form of public pressure?
    I'll think the issue is resolved when the issue is resolved. We'll have epidemiology in a year or so, I would hope. In the meantime, I simply acknowledge that public health authorities are, as they always are, unpleasantly compelled to make decisions on the basis of inadequate information.
    Quote Originally Posted by Ken G View Post
    "These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Studies and evidence on infection control report that these droplets usually travel around 6 feet (about two arms lengths)."
    So right there we have the entire basis for the "social distancing" concept, which is that the most dangerous mode for disease transmission is direct person-to-person, not indirect person-to-surface-to-person, the latter of which would not care about 6 feet (nor would the example Van Rijn just gave.) In that light, we see that the new guidance on mask wearing is consistent with the social distancing concept, because we are now less concerned about touching infected hands to our faces, and more concerned about inhaling droplets directly. We should not understress that the common language on this has just completely changed-- a month ago, all I ever heard is that I must wash my hands because I could be touching infected surfaces, but now all I hear is that surfaces are not really the main concern, direct contact with droplets flying through the air is now my concern. This is the new language I'm getting from all media outlets now, and it was quite an abrupt change (with very little mention that, oh by the way, this is totally different from what we were saying a month ago).
    Honestly, I can't respond to your personal lack of information. Droplet spray is part of the transmission of every single respiratory virus. Social distancing is the evidence-based response to that. Social distancing was in at the start of the USA's epidemic response. Your interpretation of the "language" you heard is another matter entirely, but it doesn't change the facts of the advice given, when it was given, or the reason it was given.
    Quote Originally Posted by Ken G View Post
    So masks are only "radioactive" for a few days.
    Gad, no. That's not remotely what I said. I wrote (with reference to a two-week period): "Viruses may not last that long..." I have not seen any information, one way or another, on how long SARS-CoV-2 persists in damp fabric. This whole "improvised cloth mask" thing is a new experiment, but hopefully someone's researching that, using at least some samples of common fabrics folded together in at least some of the many ways these masks are being produced. After which, the matter will be at least partially "resolved". We do know that some other coronaviruses can persist for more than a week on some surfaces, under some conditions, and we know that SARS-CoV-2 RNA was PCR-detectible on the Diamond Princess 17 days after people left their cabins (usual proviso that this does not necessarily imply infective potential). If you want my opinion, I'd extrapolate and predict that a chunk of damp fabric contaminated with SARS-CoV-2 probably wouldn't be infective after two weeks unless it was stored under some carefully controlled conditions. So viruses may well not last that long ... but I then offered a couple of reasons why you would want to wash the thing anyway.

    Grant Hutchison

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    Quote Originally Posted by Ken G View Post
    I think you have missed not only how significantly the guidance has changed, but also the reason for the change.
    I've actually been tracking it fairly closely. And it's therefore evident to me that you either missed or didn't understand the reason for the early social distancing advice from the CDC. But it was there, and it was there because they knew very well that respiratory viruses spread person-to-person by droplets.
    Further discussion on that would be useless.

    Grant Hutchison

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    Quote Originally Posted by Ken G View Post
    So you're going to ignore the fact that literally a few posts ago, your example for what you were concerned about was something that has nothing to do with 6 feet distancing? Your concern was touching a surface that was recently infected, rather than some time ago-- but not that someone was squirting droplets directly into your face and lungs? Why do you think you chose the example you chose?
    I found this to be deeply puzzling, and looking back it appears you dramatically misunderstood a comment I had made. I believe you are referring to this (please let me know if you are referring to something else):

    Quote Originally Posted by Van Rijn View Post
    Was it really claimed at one point that the primary method of transmission was by touching surfaces? I donít recall that, but am honestly not sure. I had just thought that person-to-person was primary, surface contact secondary, especially depending on how fresh the contact was. For instance, I wasnít nearly as concerned about touching my mailbox or mail hours after other contact than something handled seconds or minutes prior.
    So, as you hopefully can see, I thought that person to person transmission was primary, surface contact secondary. Within the scope of surface contact, it has been well established that the virus degrades over time, so it is reasonable to be less concerned about something that has sat around for some time vs. something recently touched. That is a comment about relative risk.

    I did not say, nor do I believe, limiting touching surfaces is more important to me than social distancing. Frankly, it surprises me you could misread my post to such a degree.

    To be very clear, my view of hand washing is that it reduces my risk in addition to personal distancing. I have never considered it to be more important than social distancing.

    Personal note: I retired a bit before this started, so I donít need to go to an office anymore and I am currently living alone. My primary response has been to focus on social distancing. Until recently, for instance, I never had groceries or dinners delivered to my home, but I am now, with no direct contact with the delivery person. Where I previously would typically drive to Home Depot or another store, I am having items delivered. I am taking some care with home deliveries, like washing my hands after opening boxes that were recently delivered, but I am not terribly concerned about things that have sat for a time, and I am not nearly as finicky about washing groceries, etc. as some of the people Iíve read about.

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    It also looks like the WHO website has some recent changes about masks, just as does the CDC website, because the WHO site (https://www.who.int/emergencies/dise...ice-for-public) states
    " If you need to leave your house, wear a mask to avoid infecting others."
    But an article (https://www.medicalnewstoday.com/art...rne#prevention) about the WHO position asserts that it states people only need to wear a face mask if they are treating a person with COVID-19 or if they are coughing and sneezing! So it sounds like the way websites can change overnight makes it a little hard to track the changing landscape, but the CDC and WHO seem to be in agreement at this point, and the changes cannot be about new information about masks, so must be because of the new stress on asymptomatic transmission.

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    Quote Originally Posted by grant hutchison View Post
    Droplet spray is part of the transmission of every single respiratory virus. Social distancing is the evidence-based response to that.
    The advice (in the UK, at least) has been remarkably consistent from day one, I thought. And fairly simple.
    1) Socially distance. This is your main defence.
    2) Wash your hands after touching potentially infective surfaces. This is your secondary defence.
    3) If you cannot socially distance then wear a mask and gloves. This is a fallback defence.
    4) If you have any hint of symptoms in your or your immediate family then self-isolate at once, only attending a hospital or doctor if it becomes worse than seasonal flu.

    There was a period when we were told not to wear a mask unless we had to - but that was when we were suffering pretty serious supply chain issues in PPE due to the sudden demand. So it was never "Masks are useless" it was always "Masks are currently a finite resource should be reserved for use in the environments where they have the greatest benefit". The only way the advice has changed, as far as I can tell, is that now the supply of PPE is more similar to the demand they have stopped asking people to avoid buying up every available mask online. I think they were very aware of the ability of people to deplete the supply of something after "the week without toilet paper".

    Is that wrong? I think that most of the confusion I've seen among my friends has been due to over-analysis of the endless reporting on the topic. The core message kind of gets washed out by a focus on what's new, which is obviously what the reporting tends to push. "No change this week" isn't a saleable headline. Its akin to health headlines like "Study says eating more blueberries prolongs life!" skipping over the fact that a balanced diet and regular exercise are still going to have more effect than a handful of berries every day. But one is new news and one isn't.

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    I agree that media reporting can easily distort or skew important information, and that may be a large part of the problem, but I just documented how things have changed, on both the CDC and WHO stances about wearing masks in public, and in particular, about the potential role of masks in limiting community spread. Perhaps the contrast was more stark in the US than the UK-- perhaps the UK did not have their Surgeon General tweet (yes tweet, sadly) "Seriously people-- STOP BUYING MASKS. They are NOT effective in preventing general public from catching #Coronavirus" He did go on to stress the need to not take masks away from healthcare workers, but certainly there is not even the slightest hint in that tweet that masks are some kind of valid fallback option for those who can't socially distance (which literally no one was doing at the time of that tweet anyway, that was Feb 29, only four days after Mardis Gras filled the streets of New Orleans and the mayor didn't dare even floating the suggestion of curtailing it). There was also no recognition that healthcare workers don't use cloth masks anyway.

    So in the US at least, the situation has changed dramatically, first there was just wash your hands, a month later it was social distance, and only just now are masks even being mentioned for public use. And that cannot be limited to one nation because as I just said, the WHO website was described as saying that masks need only be worn by symptomatic people, or people caring for them. I wish I knew how to draw from archived versions of these websites, they change so easily and rarely confess to the prior misinformation. (The same thing happens when I fix an error in one of my course websites, so I understand the phenomenon.)

    But it's also true that it doesn't really matter at this stage how much the landscape has changed, all that matters is what is done going forward. Deaths in the US are still at a rate that could lead to hundreds of thousands more before there is a vaccine, meanwhile the language is about what we can do to relax restrictions, not what do we need to do even more. I can hardly see why we shouldn't expect half a million deaths by the end of this.
    Last edited by Ken G; 2020-May-24 at 08:23 AM.

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    Quote Originally Posted by Van Rijn View Post
    I found this to be deeply puzzling, and looking back it appears you dramatically misunderstood a comment I had made. I believe you are referring to this (please let me know if you are referring to something else):
    I did indeed misrepresent you, and I have altered that post to correct the problem. I actually changed it even before you objected, because I detected the error, but that doesn't justify the mistake.

    Frankly, it surprises me you could misread my post to such a degree.
    My bad on that one.
    Last edited by Ken G; 2020-May-24 at 08:49 AM.

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