9 ms·

Short-distance aerosol transmission changes things a bit: * Social distancing isn't enough to guarantee safety in indoors spaces: bad news for bars, clubs, gym

Short-distance aerosol transmission changes things a bit: * Social distancing isn't enough to guarantee safety in indoors spaces: bad news for bars, clubs, gyms, concerts, and restaurants * Outdoors spaces are probably safer than we previously thought * Indoor mask-wearing becomes CRITICAL in public spaces * Indoor ventilation becomes extra important, using fresh air from outside or filtered/UV-sanitized air * Indoor air purifiers with HEPA ratings or UV sterilizer features may become valuable But the same overall guidance still applies: avoid crowds, wear a mask, keep your distance, outdoors activities are safer than indoors activities

DanBC 6y ago
> Indoor mask-wearing becomes CRITICAL in public spaces Mask wearing provides minimal benefits against droplet transmission, but they do nothing at all for small droplet aerosol transmission.
- misanthropian00 6y ago
  What do you consider a small droplet? The masks are tested with 0.3 micron droplets. Do you have a source?
- keenmaster 6y ago
  Studies have found that a combination of multi-layered cotton and chiffon/silk masks prevents intake of both large and small droplets. Silk/chiffon act magnetically on smaller particles to keep you from breathing them in, while the thick cotton layers stop large droplets. The aggregate effect is similar to N95, but more washable and reusable. It blows my mind that this was discovered a couple months ago and the government still hasn’t funded the mass production of such masks. After I read the study, I bought 2 masks on Etsy.com: a multilayered cotton mask and a silk mask. I wear both when I go out. What’s great is that I don’t just protect others from me, but I also protect myself from others to a large extent (as opposed to just wearing the cotton mask). As for comfort, silk is light and thin, so it doesn’t add any noticeable discomfort on top of the cotton mask. https://news.uchicago.edu/story/homemade-masks-made-silk-and-cotton-may-boost-protection https://news.uchicago.edu/story/homemade-masks-made-silk-and... Note: Newer studies have found that even just a thick cotton mask does somewhat protect you (not as much as cotton + silk of course, but they protect others from you quite effectively). You still need to be careful, generally avoid indoor environments with strangers, and socially distance. Not that that disclaimer is super necessary, because other studies have found that masks do not make people behave more recklessly :) If anything, they make you more careful and acutely aware of COVID risks.
  - DanBC 6y ago
    > Newer studies have found that even just a thick cotton mask does somewhat protect you No they haven't. If the effect of masks was so strong it would be easy to find that when we do trials. We've done the trials and we struggle to see the effect. Once we drop down the quality requirements we start to see an effect, but even that is mild. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820%2931142-9 https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820... > Although direct evidence is limited, the optimum use of face masks, in particular N95 or similar respirators in health-care settings and 12–16-layer cotton or surgical masks in the community, could depend on contextual factors; action is needed at all levels to address the paucity of better evidence. Eye protection might provide additional benefits. Globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of the challenges, but this systematic appraisal of currently best available evidence could be considered to inform interim guidance There's no way to spin phrases like "direct evidence is limited" and "paucity of evidence" to mean "we've got good quality evidence that shows an effect".
- CogentHedgehog 6y ago
  That's actually the opposite of what the evidence shows. Masks - even crappy ones, with poor mask protocol - dramatically cut infections https://arstechnica.com/science/2020/06/modeling-the-impact-of-face-masks-on-the-covid-19-pandemic/ https://arstechnica.com/science/2020/06/modeling-the-impact-... Citation: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 Remember: even if a mask doesn't effectively filter out very small particles, it still restricts the velocity of air passing through it. This means aerosolized particles will not travel as far.
  - DanBC 6y ago
    About your arstechnica link: if masks don't work all that effectively you need huge numbers of people to wear them to prevent a single infection. https://www.fhi.no/globalassets/dokumenterfiler/rapporter/2020/should-individuals-in-the-community-without-respiratory-symptoms-wear-facemasks-to-reduce-the-spread-of-covid-19-report-2020.pdf https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20... > Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community. > Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small.Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms,and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epide-miological situation. Here's all the science: we don't know if masks work or not. https://www.cebm.net/covid-19/masking-lack-of-evidence-with-politics/ https://www.cebm.net/covid-19/masking-lack-of-evidence-with-... They have a plausible mechanism of action, but they also have plausible mechanisms of harm. The above link includes one trial where they appeared to be harmful: > It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2. Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4 This is potentially because the masks start to lose effectiveness as soon as you put them on. DIY cloth masks soon become waterlogged with condensation, and then when you breath you push out aerosolised drops. https://www.ijic.info/article/view/10788 https://www.ijic.info/article/view/10788 > This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. the personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. the study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. My point is that we don't have the evidence to say whether masks work or not. You posting links to arstechnica and un-peer-reviewed pre-prints supports my point, doesn't it? If we had a Cochrane Collaboration meta analysis saying masks worked everyone would be posting that.
misanthropian00 6y ago
More emphasis on better masks that actually might prevent aerosol transmission and less emphasis on 6 foot distancing because such things matter little under aerosol conditions where air flow patterns dominate transmission. Also much more emphasis on outdoor vs indoor activities. So no it is not really the same guidance.
- CogentHedgehog 6y ago
  Your claims do not reflect what the article and the evidence it cites show. To quote: > Cowling told me that it’s better to call these “short-range aerosols,” as that communicates the nature of the threat more accurately: Most of these particles are concentrated around the infected person, but, under the right circumstances, they can accumulate and get around. This is the precise opposite of your claim that 6 foot distancing would "matter little under aerosol conditions where air flow patterns dominate transmission." AT NO POINT does the article indicate that droplets are irrelevant. We know they are the key factor in person-to-person transmission. But we also now have evidence that short-range aerosols also play a role, especially in superspreading events. The evidence is VERY clear that risks are highest in close proximity to infected individuals. I would encourage you to take another look at the article and read closely.
  - misanthropian00 6y ago
    Well first of all there is little evidence on both sides of the argument here. There isn't much evidence in favor of aerosol transmission and there isn't much evidence against it either. I would hope that more research can be done on this matter. Perhaps I worded my statement poorly. Let me try to be more precise about the idea I was trying to express. If COVID really is more aerosol infectious than we have been assuming then the 6 foot distancing would matter much less in comparison because if a cloud of infectious COVID droplets is whirling in the air currents that effect will tend to dominate in the sense that your exact location relative to the COVID+ source is no longer a direct causal factor. Yes of course being farther away makes it less likely that you will be in the path of a relatively short range aerosol cloud but the important thing in that circumstance is not to be in its path and just being farther away in the same room may not be enough to avoid it. I don't deny that if someone with COVID coughs directly in your face which apparently was considered the dominant transmission vector at first you are also likely to be infected especially if you are not fully and properly masked and goggled. That must happen sometimes. Of course being at least 6 feet away from the closest person is a good thing. It is just the assumption that that is enough to keep people safe from COVID that should be questioned more. Anyway my quibble with your post was the part about the guidelines being the same. They aren't really. The difference may be slight, but it could be critical.
graeme 6y ago
Indeed. Governments have been slow to draw these lessons unfortunately. My local government (quebec) lets you remove masks at indoors events when seated.
- CogentHedgehog 6y ago
  Governments are generally slow to change guidance when evidence is limited or ambiguous. The problem here is that while we have pretty solid evidence for short-distance aerosol transmission in some cases, it will take time to understand how BIG a factor it is. One thing that is easy to forget as a layperson: when it comes to public health, the government only has a limited ability to influence public behavior. Think of it as having a limited number of cards to play. So if they spend a card convincing people to wear masks indoors at events, then they can't spend it convincing people not to hold dinner parties (a common source of super-spreading events). Furthermore if the government emphasizes something that turns out to be ineffective, then they have even less ability to convince the public change their behavior in the future. This backlash gets worse if they appear to "change their mind" on something. Witness the backlash from health authorities shifting guidance on the importance of mask use in response to evidence of high pre-symptomatic/asymptomatic transmission of SARS-CoV-2. A huge part of the challenge for public health workers is figuring out what measures to emphasize and how to communicate it. I'm not saying the government responses are ideal: they almost never will be, especially with a new disease. But I can at least understand why they're slow to change their guidance.
  - graeme 6y ago
    This is true. However, they jumped on the deep cleaning guidance pretty quickly despite limited evidence.

DanBC 6y ago

> Indoor mask-wearing becomes CRITICAL in public spaces Mask wearing provides minimal benefits against droplet transmission, but they do nothing at all for small droplet aerosol transmission.

misanthropian00 6y ago
What do you consider a small droplet? The masks are tested with 0.3 micron droplets. Do you have a source?
keenmaster 6y ago
Studies have found that a combination of multi-layered cotton and chiffon/silk masks prevents intake of both large and small droplets. Silk/chiffon act magnetically on smaller particles to keep you from breathing them in, while the thick cotton layers stop large droplets. The aggregate effect is similar to N95, but more washable and reusable. It blows my mind that this was discovered a couple months ago and the government still hasn’t funded the mass production of such masks. After I read the study, I bought 2 masks on Etsy.com: a multilayered cotton mask and a silk mask. I wear both when I go out. What’s great is that I don’t just protect others from me, but I also protect myself from others to a large extent (as opposed to just wearing the cotton mask). As for comfort, silk is light and thin, so it doesn’t add any noticeable discomfort on top of the cotton mask. https://news.uchicago.edu/story/homemade-masks-made-silk-and-cotton-may-boost-protection https://news.uchicago.edu/story/homemade-masks-made-silk-and... Note: Newer studies have found that even just a thick cotton mask does somewhat protect you (not as much as cotton + silk of course, but they protect others from you quite effectively). You still need to be careful, generally avoid indoor environments with strangers, and socially distance. Not that that disclaimer is super necessary, because other studies have found that masks do not make people behave more recklessly :) If anything, they make you more careful and acutely aware of COVID risks.
- DanBC 6y ago
  > Newer studies have found that even just a thick cotton mask does somewhat protect you No they haven't. If the effect of masks was so strong it would be easy to find that when we do trials. We've done the trials and we struggle to see the effect. Once we drop down the quality requirements we start to see an effect, but even that is mild. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820%2931142-9 https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820... > Although direct evidence is limited, the optimum use of face masks, in particular N95 or similar respirators in health-care settings and 12–16-layer cotton or surgical masks in the community, could depend on contextual factors; action is needed at all levels to address the paucity of better evidence. Eye protection might provide additional benefits. Globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of the challenges, but this systematic appraisal of currently best available evidence could be considered to inform interim guidance There's no way to spin phrases like "direct evidence is limited" and "paucity of evidence" to mean "we've got good quality evidence that shows an effect".
CogentHedgehog 6y ago
That's actually the opposite of what the evidence shows. Masks - even crappy ones, with poor mask protocol - dramatically cut infections https://arstechnica.com/science/2020/06/modeling-the-impact-of-face-masks-on-the-covid-19-pandemic/ https://arstechnica.com/science/2020/06/modeling-the-impact-... Citation: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 Remember: even if a mask doesn't effectively filter out very small particles, it still restricts the velocity of air passing through it. This means aerosolized particles will not travel as far.
- DanBC 6y ago
  About your arstechnica link: if masks don't work all that effectively you need huge numbers of people to wear them to prevent a single infection. https://www.fhi.no/globalassets/dokumenterfiler/rapporter/2020/should-individuals-in-the-community-without-respiratory-symptoms-wear-facemasks-to-reduce-the-spread-of-covid-19-report-2020.pdf https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20... > Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community. > Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small.Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms,and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epide-miological situation. Here's all the science: we don't know if masks work or not. https://www.cebm.net/covid-19/masking-lack-of-evidence-with-politics/ https://www.cebm.net/covid-19/masking-lack-of-evidence-with-... They have a plausible mechanism of action, but they also have plausible mechanisms of harm. The above link includes one trial where they appeared to be harmful: > It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2. Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4 This is potentially because the masks start to lose effectiveness as soon as you put them on. DIY cloth masks soon become waterlogged with condensation, and then when you breath you push out aerosolised drops. https://www.ijic.info/article/view/10788 https://www.ijic.info/article/view/10788 > This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. the personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. the study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. My point is that we don't have the evidence to say whether masks work or not. You posting links to arstechnica and un-peer-reviewed pre-prints supports my point, doesn't it? If we had a Cochrane Collaboration meta analysis saying masks worked everyone would be posting that.

misanthropian00 6y ago

More emphasis on better masks that actually might prevent aerosol transmission and less emphasis on 6 foot distancing because such things matter little under aerosol conditions where air flow patterns dominate transmission. Also much more emphasis on outdoor vs indoor activities. So no it is not really the same guidance.

CogentHedgehog 6y ago
Your claims do not reflect what the article and the evidence it cites show. To quote: > Cowling told me that it’s better to call these “short-range aerosols,” as that communicates the nature of the threat more accurately: Most of these particles are concentrated around the infected person, but, under the right circumstances, they can accumulate and get around. This is the precise opposite of your claim that 6 foot distancing would "matter little under aerosol conditions where air flow patterns dominate transmission." AT NO POINT does the article indicate that droplets are irrelevant. We know they are the key factor in person-to-person transmission. But we also now have evidence that short-range aerosols also play a role, especially in superspreading events. The evidence is VERY clear that risks are highest in close proximity to infected individuals. I would encourage you to take another look at the article and read closely.
- misanthropian00 6y ago
  Well first of all there is little evidence on both sides of the argument here. There isn't much evidence in favor of aerosol transmission and there isn't much evidence against it either. I would hope that more research can be done on this matter. Perhaps I worded my statement poorly. Let me try to be more precise about the idea I was trying to express. If COVID really is more aerosol infectious than we have been assuming then the 6 foot distancing would matter much less in comparison because if a cloud of infectious COVID droplets is whirling in the air currents that effect will tend to dominate in the sense that your exact location relative to the COVID+ source is no longer a direct causal factor. Yes of course being farther away makes it less likely that you will be in the path of a relatively short range aerosol cloud but the important thing in that circumstance is not to be in its path and just being farther away in the same room may not be enough to avoid it. I don't deny that if someone with COVID coughs directly in your face which apparently was considered the dominant transmission vector at first you are also likely to be infected especially if you are not fully and properly masked and goggled. That must happen sometimes. Of course being at least 6 feet away from the closest person is a good thing. It is just the assumption that that is enough to keep people safe from COVID that should be questioned more. Anyway my quibble with your post was the part about the guidelines being the same. They aren't really. The difference may be slight, but it could be critical.

graeme 6y ago

Indeed. Governments have been slow to draw these lessons unfortunately. My local government (quebec) lets you remove masks at indoors events when seated.

CogentHedgehog 6y ago
Governments are generally slow to change guidance when evidence is limited or ambiguous. The problem here is that while we have pretty solid evidence for short-distance aerosol transmission in some cases, it will take time to understand how BIG a factor it is. One thing that is easy to forget as a layperson: when it comes to public health, the government only has a limited ability to influence public behavior. Think of it as having a limited number of cards to play. So if they spend a card convincing people to wear masks indoors at events, then they can't spend it convincing people not to hold dinner parties (a common source of super-spreading events). Furthermore if the government emphasizes something that turns out to be ineffective, then they have even less ability to convince the public change their behavior in the future. This backlash gets worse if they appear to "change their mind" on something. Witness the backlash from health authorities shifting guidance on the importance of mask use in response to evidence of high pre-symptomatic/asymptomatic transmission of SARS-CoV-2. A huge part of the challenge for public health workers is figuring out what measures to emphasize and how to communicate it. I'm not saying the government responses are ideal: they almost never will be, especially with a new disease. But I can at least understand why they're slow to change their guidance.
- graeme 6y ago
  This is true. However, they jumped on the deep cleaning guidance pretty quickly despite limited evidence.