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  #1  
Old 05-28-2020, 09:54 AM
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Default The face-masks for covid info thread

A poster recently asked a bunch of questions about masks. I found it a little tiresome because it was mostly stuff we'd discussed before, but of course, it was new to HIM. And while that discussion was good, it's now buried in a thread about other stuff. So I'm creating this thread for discussion about the efficacy of masks, so other posters can find info if they want it.

I'm going to try to be careful in distinguishing when a mask provides useful protection for the wearer and when it provides protection from the wearer, and use "for" and "from" as shorthand.

"For" means wearing a certain type of mask reduces the wearer's risk of getting infected. "From" means that if the wearer is sick, or is pre-symptomatic (or asymptomatic) the mask reduces the risk that others will catch covid or other illnesses from the wearer.
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Old 05-28-2020, 09:55 AM
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Quidence from CDC and WHO early in the pandemic. Thanks Campbell and satagaeru.

http://www.actuarialoutpost.com/actu...5&postcount=32

Quote:
Originally Posted by satogaeru View Post
Here is the archived original CDC guidance.

Quote:
Originally Posted by CDC
Wear a facemask if you are sick
If you are sick: You should wear a facemask when you are around other people (e.g., sharing a room or vehicle) and before you enter a healthcare providerĺs office. If you are not able to wear a facemask (for example, because it causes trouble breathing), then you should do your best to cover your coughs and sneezes, and people who are caring for you should wear a facemask if they enter your room. Learn what to do if you are sick.
If you are NOT sick: You do not need to wear a facemask unless you are caring for someone who is sick (and they are not able to wear a facemask). Facemasks may be in short supply and they should be saved for caregivers.
and

Quote:
Originally Posted by campbell View Post
From March 31:
https://www.cnn.com/2020/03/30/world...a1XSojIqjQhzps

http://www.actuarialoutpost.com/actu...5&postcount=21

WHO stands by recommendation to not wear masks if you are not sick or not caring for someone who is sick

Spoiler:
(CNN)World Health Organization officials Monday said they still recommend people not wear face masks unless they are sick with Covid-19 or caring for someone who is sick.

Spoiler:
Masks may actually increase your coronavirus risk if worn improperly, surgeon general warns
Masks may actually increase your coronavirus risk if worn improperly, surgeon general warns
"There is no specific evidence to suggest that the wearing of masks by the mass population has any potential benefit. In fact, there's some evidence to suggest the opposite in the misuse of wearing a mask properly or fitting it properly," Dr. Mike Ryan, executive director of the WHO health emergencies program, said at a media briefing in Geneva, Switzerland, on Monday.
"There also is the issue that we have a massive global shortage," Ryan said about masks and other medical supplies. "Right now the people most at risk from this virus are frontline health workers who are exposed to the virus every second of every day. The thought of them not having masks is horrific."
People around the country are sewing masks. And some hospitals, facing dire shortage, welcome them
People around the country are sewing masks. And some hospitals, facing dire shortage, welcome them
Dr. Maria Van Kerkhove, an infectious disease epidemiologist with the WHO, also said at Monday's briefing that it is important "we prioritize the use of masks for those who need it most," which would be frontline health care workers.
"In the community, we do not recommend the use of wearing masks unless you yourself are sick and as a measure to prevent onward spread from you if you are ill," Van Kerkhove said.

"The masks that we recommend are for people who are at home and who are sick and for those individuals who are caring for those people who are home that are sick," she said.
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Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

World Health Organization officials warned at a media briefing last week that globally there is a "significant shortage" of medical supplies, including personal protective gear or PPE, for doctors.
"We need to be clear," Van Kerkhove said last week. "The world is facing a significant shortage of PPE for our frontline workers -- including masks and gloves and gowns and face shields -- and protecting our health care workers must be the top priority for use of this PPE."

Last edited by Lucy; 06-01-2020 at 09:31 AM..
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Old 05-28-2020, 09:55 AM
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current, "community should wear masks" cdc guidence

https://www.cdc.gov/coronavirus/2019...ace-cover.html

Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission

https://www.cdc.gov/coronavirus/2019...ace-cover.html

Quote:
CDC continues to study the spread and effects of the novel coronavirus across the United States. We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms (“asymptomatic”) and that even those who eventually develop symptoms (“pre-symptomatic”) can transmit the virus to others before showing symptoms. This means that the virus can spread between people interacting in close proximity—for example, speaking, coughing, or sneezing—even if those people are not exhibiting symptoms. 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) especially in areas of significant community-based transmission.

It is critical to emphasize that maintaining 6-feet social distancing remains important to slowing the spread of the virus. CDC is additionally advising the use of simple cloth face coverings to slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others. Cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure.

The cloth face coverings recommended are not surgical masks or N-95 respirators. Those are critical supplies that must continue to be reserved for healthcare workers and other medical first responders, as recommended by current CDC guidance.

Last edited by Lucy; 05-28-2020 at 10:35 AM..
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  #4  
Old 05-28-2020, 10:03 AM
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2015 peer-reviewed study in Vietnamese hospital of the efficacy for healthcare workers of wearing surgical masks, cloth masks, or "common practice" (which was a mix of wearing surgical or cloth masks). It doesn't say what sort of cloth mask was used.

abstract,
https://bmjopen.bmj.com/content/5/4/e006577
full stody
https://bmjopen.bmj.com/content/bmjo...06577.full.pdf
comments from the authors about what to do if there aren't enough medical masks to go around.
https://bmjopen.bmj.com/content/5/4/...-a-last-resort

The conclusion was that health care workers who wore medical masks caught fewer respiratory bugs than those who wore cloth masks, and the control group (which wore a mix of both types) was in between. The authors recommended against the use of cloth masks. But in their update, they point out that they were comparing cloth to medical, not to "nothing", and they say:

Quote:
Health workers are asking us if they should wear no mask at all if cloth masks are the only option. Our research does not condone health workers working unprotected. We recommend that health workers should not work during the COVID-19 pandemic without respiratory protection as a matter of work health and safety. In addition, if health workers get infected, high rates of staff absenteeism from illness may also affect health system capacity to respond. Some health workers may still choose to work in inadequate PPE. In this case, the physical barrier provided by a cloth mask may afford some protection, but likely much less than a surgical mask or a respirator.
Note that this study is a pure "for" study, with no "from" component.
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Old 05-28-2020, 10:09 AM
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Spoilered for size

Spoiler:
__________________
"I'm tryin' to think, but nuthin' happens!"
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Old 05-28-2020, 10:09 AM
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Survey of a bunch of hastily assembled studies on mask use (thanks to Incredible Hulctuary)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7191274/

Quote:
Results
A total of 19 randomised controlled trials were included in this study – 8 in community settings, 6 in healthcare settings and 5 as source control. Most of these randomised controlled trials used different interventions and outcome measures. In the community, masks appeared to be more effective than hand hygiene alone, and both together are more protective. Randomised controlled trials in health care workers showed that respirators, if worn continually during a shift, were effective but not if worn intermittently. Medical masks were not effective, and cloth masks even less effective. When used by sick patients randomised controlled trials suggested protection of well contacts.

Conclusion
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. Trials in healthcare workers support the use of respirators continuously during a shift. This may prevent health worker infections and deaths from COVID-19, as aerosolisation in the hospital setting has been documented.
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Old 05-28-2020, 10:16 AM
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From Polevault, Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach

https://www.acpjournals.org/doi/10.7326/M20-2567

This one is primarily "from" focused, although it mentioned some protection for masked rabbits in a study about tuberculosis.

Quote:
Cloth can block droplets and aerosols, and layers add efficiency. Filtration efficiency for single layers of different types of cotton cloth in a bioaerosol (0.2 Ám) experiment was between 43% and 94%, compared with 98% to 99% for fabric from disposable medical masks (2). In a summary of similar observations, single layers of scarfs, sweatshirts, T-shirts, and towels were associated with filtration efficiency of 10% to 40% in experiments using NaCl aerosol (0.075 Ám) (3). For tea towel fabric, studied with aerosol-sized particles, filtration efficiency in experiments using a bacterial marker was 83% with 1 layer and 97% with 2 layers, compared with 96% for a medical mask (4). In experiments using virus, 1 layer of tea towel had 72% efficiency and 1 layer of T-shirt fabric 51%, compared with 90% for a medical mask (4). A 2020 study confirms that some fabrics block clinically useful percentages of transmission, even for aerosols and even in single layers; multiple layers improve efficiency (5).

Outward protection for cloth masks was extensively studied decades ago, and the results are highly relevant today. Compared with bacteria recovery from unmasked volunteers, a mask made of muslin and flannel reduced bacteria recovered on agar sedimentation plates by 99.3% to 99.9%, total airborne microorganisms by 99.5% to 99.8%, and bacteria recovered from aerosols (<4 Ám) by 88% to 99% (6). A similar experiment in 1975 compared 4 medical masks and 1 commercially produced reusable mask made of 4 layers of cotton muslin (7). Filtration efficiency, assessed by bacterial counts, was 96% to 99% for the medical masks and 99% for the cloth mask; for aerosols (<3.3 Ám), it was 72% to 89% and 89%, respectively.
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Old 05-28-2020, 10:19 AM
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Again thanks to Incredible Hulctuary, a study regarding Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks

https://pubs.acs.org/doi/10.1021/acsnano.0c03252

Quote:
In conclusion, we have measured the filtration efficiencies of various commonly available fabrics for use as cloth masks in filtering particles in the significant (for aerosol-based virus transmission) size range of ∼10 nm to ∼6 μm and have presented filtration efficiency data as a function of aerosol particle size. We find that cotton, natural silk, and chiffon can provide good protection, typically above 50% in the entire 10 nm to 6.0 μm range, provided they have a tight weave. Higher threads per inch cotton with tighter weaves resulted in better filtration efficiencies. For instance, a 600 TPI cotton sheet can provide average filtration efficiencies of 79 ▒ 23% (in the 10 nm to 300 nm range) and 98.4 ▒ 0.2% (in the 300 nm to 6 μm range). A cotton quilt with batting provides 96 ▒ 2% (10 nm to 300 nm) and 96.1 ▒ 0.3% (300 nm to 6 μm). Likely the highly tangled fibrous nature of the batting aids in the superior performance at small particle sizes. Materials such as silk and chiffon are particularly effective (considering their sheerness) at excluding particles in the nanoscale regime (<∼100 nm), likely due to electrostatic effects that result in charge transfer with nanoscale aerosol particles.
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Old 05-28-2020, 10:26 AM
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A study about the importance of fit, showing the improved efficacy of various types of masks when adding a "nylon overlayer"

Quantitative Method for Comparative Assessment of Particle Filtration Efficiency of Fabric Masks as Alternatives to Standard Surgical Masks for PPE
https://www.medrxiv.org/content/10.1...567v4.full.pdf

And a more readable summary of the takeaway, which is that you can make almost any mask work pretty well if you use a slice of a nylon stocking to hold it tightly over your face, complete with an illustration of how to do that:

Adding A Nylon Stocking Layer Could Boost Protection From Cloth Masks, Study Finds
https://www.npr.org/sections/goatsan...sks-study-find
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Old 05-28-2020, 10:30 AM
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Another from Polevault, this one documenting the size of respiratory droplets in various circumstances

Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

Quantitative Method for Comparative Assessment of Particle Filtration Efficiency of Fabric Masks 2 as Alternatives to Standard Surgical Masks for PPE

Quote:
Originally Posted by Polevault
This study says that most droplets from human respiration are between 100 and 1000 nanometers, which is basically the sweet spot in the graph for the 80 TPI masks.
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