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Have surgical masks really shown to be effective in reducing the spread of disease when worn by people who are not yet infected? I've been to mainland China, T

Have surgical masks really shown to be effective in reducing the spread of disease when worn by people who are not yet infected? I've been to mainland China, Taiwan, HK, South Korea, Japan, Vietnam, Singapore, Malaysia and Thailand in the last four weeks. China has close to 100% usage of masks in public, mostly the surgical type. The virus is spreading like wildfire there. Every other country I've visited has markedly less mask usage, in particular Vietnam where at least in the south, it's relatively rare to see people wearing them. Yet in all the other countries it's hardly spreading (obviously I'm excluding the cruise ship off the coast of Japan here, which appears to be a special case).

pbourke 7y ago
Absence of evidence is not evidence of absence. A number of public health authorities, including the US CDC, have stated that there is likely community transmission happening.
whatshisface 7y ago
How do you know if your cough is due to smog or due to infection? Best to wear the mask anyway.
- _-___________-_ 7y ago
  Well, the best available estimate of the chance that I'm infected is on the order of 0.00001%, give or take an order of magnitude. If I would take countermeasures to every risk of that order, I wouldn't have time to do anything else.
  - whatshisface 7y ago
    That number really depends on where you live right now.
    - _-___________-_ 7y ago
      Not as much as you'd think. It's basically "mainland China or a cruise ship" or "anywhere else".
      - whatshisface 7y ago
        Isn't mainland China the only place where people are really wearing masks because of this?
        _-___________-_ 7y ago
        Yes, it's simultaneously the only place with close to 100% mask usage, and the only place with significant spread of it.
        benibela 7y ago
        From this one could conclude, that masks are spreading the virus
        _-___________-_ 7y ago
        correlation != causation It does however provide a data point that masks are likely not very effective at preventing the spread of the virus.
        swsieber 7y ago
        That's like saying cancer treatment centers aren't very good at helping people survive because many people who visit them die. So maybe you're right. But maybe it would have broken out 100x worse by now.
        _-___________-_ 7y ago
        Again: there are other countries where the virus has spread in the community, yet despite virtually no mask wearing the spread has been extremely limited and easily controlled.
chrisco255 7y ago
No, I believe I read that the typical N95 masks that people use is basically useless against this virus, because it's very, very tiny and can sail right through a mask. It still might reduce your exposure and is probably better than nothing, but I believe only a gas mask would totally protect you. "...there's no evidence inexpensive surgical masks can protect against flu virus particles small enough to be inhaled into the lower respiratory tract or the lungs" http://www.digitaljournal.com/life/health/do-face-masks-help-protect-users-against-coronavirus-infecdtions/article/565812 http://www.digitaljournal.com/life/health/do-face-masks-help...
- _-___________-_ 7y ago
  Most people are not even wearing N95 masks, they're wearing the much more common and cheaper "surgical masks" that don't form any kind of seal around the outside.
- zone411 7y ago
  Your own cite says that surgical masks are ineffective but properly fitted N95 masks can be effective. I believe that they filter droplets well, e.g. from sneezing. https://www.asahq.org/about-asa/governance-and-committees/asa-committees/committee-on-occupational-health/coronavirus https://www.asahq.org/about-asa/governance-and-committees/as...
  - chrisco255 7y ago
    I think they're better than nothing but as someone else mentioned the virus is 0.1 to 0.3 microns and the N95 only filters 95% of particles 3 microns or larger.
    - _-___________-_ 7y ago
      I haven't seen conclusive evidence that they're better than nothing.
      - pmorici 7y ago
autoconfig 7y ago
There are studies that show that masks (surgical and n95) can help prevent healthy people from getting infected [1][2]. Everyone I've seen claiming the opposite (including supposed experts being interviewed) usually do it without any significant data to back it up (just some high level theorizing). I also rarely see anyone discussing the nuances of efficacy against airborne vs droplet spread viruses. Using just a minimum amount of reasoning it would seem very plausible that masks would be effective against droplets but less effective against airborne diseases. [1] https://www.newscientist.com/article/dn3692-face-masks-are-best-protection-against-sars/ https://www.newscientist.com/article/dn3692-face-masks-are-b... [2] https://annals.org/aim/fullarticle/744899/facemasks-hand-hygiene-prevent-influenza-transmission-households-cluster-randomized-trial https://annals.org/aim/fullarticle/744899/facemasks-hand-hyg...
- _-___________-_ 7y ago
  Public health authorities like CDC don't recommend their use among people who are not infected: CDC does not recommend that people who are well wear [a] facemask to protect themselves from respiratory viruses, including 2019-nCoV. - https://www.cdc.gov/coronavirus/2019-ncov/about/prevention-treatment.html https://www.cdc.gov/coronavirus/2019-ncov/about/prevention-t... Now, I'm not one to blindly trust a government agency, but most of the evidence seems inconclusive at this point, and one thing can't be ignored: in mainland China, use of masks in public spaces is near 100%, yet the virus is spreading rapidly. Outside mainland China, far fewer people are wearing masks, yet the virus is not spreading much at all.
  - zxcmx 7y ago
    Not quite sure I get the reasoning in that link. Sure, it's not likely to decrease your direct infection risk. But it does decrease the risk of you infecting others. At any given time you can't really know if you're infected or not if the virus is widespread. Also the mask would presumably be more effective than coughing into your elbow or a tissue, which they do recommend. So why not wear them? Why recommend them for healthcare workers but not the general public? I'm wondering if the unstated reasoning is that widespread mask usage freaks people out and increases the chance of large scale panic.
thaumasiotes 7y ago
> Have surgical masks really shown to be effective in reducing the spread of disease when worn by people who are not yet infected? > China has close to 100% usage of masks in public You know, 100% usage in public is an excellent way to ensure that people who are infected wear the masks.
- _-___________-_ 7y ago
  I agree. But other countries have no significant community spread besides not much mask usage.
electriclove 7y ago
Are you still traveling to these countries? Are you concerned?
- _-___________-_ 7y ago
  Yes, all of them except mainland China. I'm not the slightest bit concerned. No country except mainland China has more than 70 confirmed cases, and deaths worldwide are in the single digits outside of China. These are countries with millions, tens of millions or hundreds of millions of inhabitants. I'm heading to Singapore in a few days, which has the most cases outside of mainland China (likely because they're very good at tracking them) -- 67 out of a population of 5.7 million (0.00001%), and of course all of those people are in quarantine. I imagine some cases haven't been discovered yet, but I have a hard time imagining that changing the order of magnitude. I'd be willing to travel to many parts of mainland China, but it causes problems for traveling to other countries, so I'm unable to for now. I'll alter my travel according to the facts as they change, but for now there's absolutely no rational reason I can see for avoiding travel to any country other than mainland China. Edited to add: numbers are from https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200215-sitrep-26-covid-19.pdf https://www.who.int/docs/default-source/coronaviruse/situati...
  - mlyle 7y ago
    Probably the main reason to consider travel slightly hazardous is that you'll be in close proximity to other travelers and people who service travelers, which likely represents some risk. What if a group of Chinese nationals traveling to a tour get on your plane / bus / etc, or were the previous people in your seat? You don't have that high of a risk from this scenario, but it is more exposure than you'd get at home.
    - _-___________-_ 7y ago
      Most organised outbound tourism from China is canceled right now, though there are of course still independent travelers and probably smaller group travel too. It's also worth noting that the fact that they're Chinese nationals doesn't really move the needle that much on how likely it is that they're infected. About 0.00005% of the mainland China resident population is confirmed to be infected, and the vast majority of those (over 80%) are in Hubei, which given the lockdown makes it very unlikely that you will meet them on an aircraft. Even if you allow for under-reporting the order of magnitude is probably about right. Additionally there are another 50 million Chinese nationals living in other countries, who I would submit are more likely than those resident in China to be traveling right now, and are also far less likely to be infected. This is one reason why the racism seen recently in Australia and UK against Chinese-looking people wearing masks is so ridiculous.
pmorici 7y ago
Surgical masks are meant to stop droplets and large particles but aren't rated to filter airborne particulates. These more or less protect people from sneezing or coughing directly onto one another. The next step up from a surgical mask is an NIOSH rated mask / respirator. These carry a letter and number rating the letter is either N, R, or P and the number is typically 95 - 100. N95 is a NIOSH filter rating and where the term N95 mask comes from. These will filter out any viruses and other particulates in the air. There are studies showing that N95 Masks are effective. https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/respsource3healthcare.html https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part... edit: all that said there are studies that show both types have similar effectiveness at preventing infections in healthcare workers so I wouldn't go around telling people that any of them are useless. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/
throwawayhhakdl 7y ago
The important bit is that they’re not “practically” effective. You need to wear them properly. You need to change them regularly. You need to practice effective hygiene like not touching your face. If the government distributed masks that could be effective to everyone, it’s unlikely they would have a noticeable effect
physicles 7y ago
Yeah not only are surgical masks not even clinically effective in this situation, they’re often not worn properly. I’m in Beijing now and you see people with masks not covering their nose, or worse, pulled down onto their chin. A friend of mine tried to remind an older lady in an elevator about proper mask usage, and her response was 你们年轻人管太多了 — you young people worry too much/should mind your own business. The people in my compound who were confirmed to have the virus (we found out on the 12th) got it at a family gathering over the new year holiday in Shanghai. So obviously they weren’t wearing a mask then. What seems to be making a difference in China — it’s no longer spreading like wildfire, if you believe the official reports* — is self-quarantine. Most of my friends have barely left home since the beginning of February. For a while, some restaurants that were still open wouldn’t let people sit together in parties larger than 2. And at least in Beijing, everyone who returns to the city after travel must undergo mandatory 14 day home quarantine, with fines or punishments for those caught violating (https://www.nytimes.com/reuters/2020/02/14/world/asia/14reuters-china-health-beijing.html https://www.nytimes.com/reuters/2020/02/14/world/asia/14reut... though enforcement varies from place to place). * Wuhan/Hubei are a tragedy no matter how you count. But at least Beijing is doing OK. I mostly trust the official numbers, simply because the Party has a strong vested interest in mounting a response commensurate with the threat. They can’t let the virus spread too much and rip apart the capital; neither can they afford to tank the economy for several months longer than necessary to contain the threat. Even with all the censorship, if you find yourself fighting against reality, reality wins.
oarsinsync 7y ago
> I've been to mainland China, ... HK ... in the last four weeks. China has close to 100% usage of masks in public, mostly the surgical type. The virus is spreading like wildfire there. Every other country I've visited has markedly less mask usage. I dunno where you were in HK, but the only place I haven't seen everyone wearing a mask is in Soho. Everywhere else, I'm seeing near 100% coverage.
- _-___________-_ 7y ago
  I would have put it closer to 2/3 or 3/4 in HK, versus almost 100% in China. I'm usually around Yuen Long, Mong Kok, TST, Central and Western. Has been a week since I was there though. Compared to mainland China and HK, there's way less mask usage elsewhere. For example in Vietnam I'd say it's more like 5-10%, at least in the south.

pbourke 7y ago

Absence of evidence is not evidence of absence. A number of public health authorities, including the US CDC, have stated that there is likely community transmission happening.

whatshisface 7y ago

How do you know if your cough is due to smog or due to infection? Best to wear the mask anyway.

_-___________-_ 7y ago
Well, the best available estimate of the chance that I'm infected is on the order of 0.00001%, give or take an order of magnitude. If I would take countermeasures to every risk of that order, I wouldn't have time to do anything else.
- whatshisface 7y ago
  That number really depends on where you live right now.
  - _-___________-_ 7y ago
    Not as much as you'd think. It's basically "mainland China or a cruise ship" or "anywhere else".
    - whatshisface 7y ago
      Isn't mainland China the only place where people are really wearing masks because of this?
      - _-___________-_ 7y ago
        Yes, it's simultaneously the only place with close to 100% mask usage, and the only place with significant spread of it.
        benibela 7y ago
        From this one could conclude, that masks are spreading the virus
        _-___________-_ 7y ago
        correlation != causation It does however provide a data point that masks are likely not very effective at preventing the spread of the virus.
        swsieber 7y ago
        That's like saying cancer treatment centers aren't very good at helping people survive because many people who visit them die. So maybe you're right. But maybe it would have broken out 100x worse by now.
        _-___________-_ 7y ago
        Again: there are other countries where the virus has spread in the community, yet despite virtually no mask wearing the spread has been extremely limited and easily controlled.

chrisco255 7y ago

No, I believe I read that the typical N95 masks that people use is basically useless against this virus, because it's very, very tiny and can sail right through a mask. It still might reduce your exposure and is probably better than nothing, but I believe only a gas mask would totally protect you. "...there's no evidence inexpensive surgical masks can protect against flu virus particles small enough to be inhaled into the lower respiratory tract or the lungs" http://www.digitaljournal.com/life/health/do-face-masks-help-protect-users-against-coronavirus-infecdtions/article/565812 http://www.digitaljournal.com/life/health/do-face-masks-help...

_-___________-_ 7y ago
Most people are not even wearing N95 masks, they're wearing the much more common and cheaper "surgical masks" that don't form any kind of seal around the outside.
zone411 7y ago
Your own cite says that surgical masks are ineffective but properly fitted N95 masks can be effective. I believe that they filter droplets well, e.g. from sneezing. https://www.asahq.org/about-asa/governance-and-committees/asa-committees/committee-on-occupational-health/coronavirus https://www.asahq.org/about-asa/governance-and-committees/as...
- chrisco255 7y ago
  I think they're better than nothing but as someone else mentioned the virus is 0.1 to 0.3 microns and the N95 only filters 95% of particles 3 microns or larger.
  - _-___________-_ 7y ago
    I haven't seen conclusive evidence that they're better than nothing.
    - pmorici 7y ago

autoconfig 7y ago

There are studies that show that masks (surgical and n95) can help prevent healthy people from getting infected [1][2]. Everyone I've seen claiming the opposite (including supposed experts being interviewed) usually do it without any significant data to back it up (just some high level theorizing). I also rarely see anyone discussing the nuances of efficacy against airborne vs droplet spread viruses. Using just a minimum amount of reasoning it would seem very plausible that masks would be effective against droplets but less effective against airborne diseases. [1] https://www.newscientist.com/article/dn3692-face-masks-are-best-protection-against-sars/ https://www.newscientist.com/article/dn3692-face-masks-are-b... [2] https://annals.org/aim/fullarticle/744899/facemasks-hand-hygiene-prevent-influenza-transmission-households-cluster-randomized-trial https://annals.org/aim/fullarticle/744899/facemasks-hand-hyg...

_-___________-_ 7y ago
Public health authorities like CDC don't recommend their use among people who are not infected: CDC does not recommend that people who are well wear [a] facemask to protect themselves from respiratory viruses, including 2019-nCoV. - https://www.cdc.gov/coronavirus/2019-ncov/about/prevention-treatment.html https://www.cdc.gov/coronavirus/2019-ncov/about/prevention-t... Now, I'm not one to blindly trust a government agency, but most of the evidence seems inconclusive at this point, and one thing can't be ignored: in mainland China, use of masks in public spaces is near 100%, yet the virus is spreading rapidly. Outside mainland China, far fewer people are wearing masks, yet the virus is not spreading much at all.
- zxcmx 7y ago
  Not quite sure I get the reasoning in that link. Sure, it's not likely to decrease your direct infection risk. But it does decrease the risk of you infecting others. At any given time you can't really know if you're infected or not if the virus is widespread. Also the mask would presumably be more effective than coughing into your elbow or a tissue, which they do recommend. So why not wear them? Why recommend them for healthcare workers but not the general public? I'm wondering if the unstated reasoning is that widespread mask usage freaks people out and increases the chance of large scale panic.

thaumasiotes 7y ago

> Have surgical masks really shown to be effective in reducing the spread of disease when worn by people who are not yet infected? > China has close to 100% usage of masks in public You know, 100% usage in public is an excellent way to ensure that people who are infected wear the masks.

_-___________-_ 7y ago
I agree. But other countries have no significant community spread besides not much mask usage.

electriclove 7y ago

Are you still traveling to these countries? Are you concerned?

_-___________-_ 7y ago
Yes, all of them except mainland China. I'm not the slightest bit concerned. No country except mainland China has more than 70 confirmed cases, and deaths worldwide are in the single digits outside of China. These are countries with millions, tens of millions or hundreds of millions of inhabitants. I'm heading to Singapore in a few days, which has the most cases outside of mainland China (likely because they're very good at tracking them) -- 67 out of a population of 5.7 million (0.00001%), and of course all of those people are in quarantine. I imagine some cases haven't been discovered yet, but I have a hard time imagining that changing the order of magnitude. I'd be willing to travel to many parts of mainland China, but it causes problems for traveling to other countries, so I'm unable to for now. I'll alter my travel according to the facts as they change, but for now there's absolutely no rational reason I can see for avoiding travel to any country other than mainland China. Edited to add: numbers are from https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200215-sitrep-26-covid-19.pdf https://www.who.int/docs/default-source/coronaviruse/situati...
- mlyle 7y ago
  Probably the main reason to consider travel slightly hazardous is that you'll be in close proximity to other travelers and people who service travelers, which likely represents some risk. What if a group of Chinese nationals traveling to a tour get on your plane / bus / etc, or were the previous people in your seat? You don't have that high of a risk from this scenario, but it is more exposure than you'd get at home.
  - _-___________-_ 7y ago
    Most organised outbound tourism from China is canceled right now, though there are of course still independent travelers and probably smaller group travel too. It's also worth noting that the fact that they're Chinese nationals doesn't really move the needle that much on how likely it is that they're infected. About 0.00005% of the mainland China resident population is confirmed to be infected, and the vast majority of those (over 80%) are in Hubei, which given the lockdown makes it very unlikely that you will meet them on an aircraft. Even if you allow for under-reporting the order of magnitude is probably about right. Additionally there are another 50 million Chinese nationals living in other countries, who I would submit are more likely than those resident in China to be traveling right now, and are also far less likely to be infected. This is one reason why the racism seen recently in Australia and UK against Chinese-looking people wearing masks is so ridiculous.

pmorici 7y ago

Surgical masks are meant to stop droplets and large particles but aren't rated to filter airborne particulates. These more or less protect people from sneezing or coughing directly onto one another. The next step up from a surgical mask is an NIOSH rated mask / respirator. These carry a letter and number rating the letter is either N, R, or P and the number is typically 95 - 100. N95 is a NIOSH filter rating and where the term N95 mask comes from. These will filter out any viruses and other particulates in the air. There are studies showing that N95 Masks are effective. https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/respsource3healthcare.html https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part... edit: all that said there are studies that show both types have similar effectiveness at preventing infections in healthcare workers so I wouldn't go around telling people that any of them are useless. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/

throwawayhhakdl 7y ago

The important bit is that they’re not “practically” effective. You need to wear them properly. You need to change them regularly. You need to practice effective hygiene like not touching your face. If the government distributed masks that could be effective to everyone, it’s unlikely they would have a noticeable effect

physicles 7y ago

Yeah not only are surgical masks not even clinically effective in this situation, they’re often not worn properly. I’m in Beijing now and you see people with masks not covering their nose, or worse, pulled down onto their chin. A friend of mine tried to remind an older lady in an elevator about proper mask usage, and her response was 你们年轻人管太多了 — you young people worry too much/should mind your own business. The people in my compound who were confirmed to have the virus (we found out on the 12th) got it at a family gathering over the new year holiday in Shanghai. So obviously they weren’t wearing a mask then. What seems to be making a difference in China — it’s no longer spreading like wildfire, if you believe the official reports* — is self-quarantine. Most of my friends have barely left home since the beginning of February. For a while, some restaurants that were still open wouldn’t let people sit together in parties larger than 2. And at least in Beijing, everyone who returns to the city after travel must undergo mandatory 14 day home quarantine, with fines or punishments for those caught violating (https://www.nytimes.com/reuters/2020/02/14/world/asia/14reuters-china-health-beijing.html https://www.nytimes.com/reuters/2020/02/14/world/asia/14reut... though enforcement varies from place to place). * Wuhan/Hubei are a tragedy no matter how you count. But at least Beijing is doing OK. I mostly trust the official numbers, simply because the Party has a strong vested interest in mounting a response commensurate with the threat. They can’t let the virus spread too much and rip apart the capital; neither can they afford to tank the economy for several months longer than necessary to contain the threat. Even with all the censorship, if you find yourself fighting against reality, reality wins.

oarsinsync 7y ago

> I've been to mainland China, ... HK ... in the last four weeks. China has close to 100% usage of masks in public, mostly the surgical type. The virus is spreading like wildfire there. Every other country I've visited has markedly less mask usage. I dunno where you were in HK, but the only place I haven't seen everyone wearing a mask is in Soho. Everywhere else, I'm seeing near 100% coverage.

_-___________-_ 7y ago
I would have put it closer to 2/3 or 3/4 in HK, versus almost 100% in China. I'm usually around Yuen Long, Mong Kok, TST, Central and Western. Has been a week since I was there though. Compared to mainland China and HK, there's way less mask usage elsewhere. For example in Vietnam I'd say it's more like 5-10%, at least in the south.