Coronavirus drifts through the air in microscopic droplets – the science of infectious aerosols

  1. Buffaloed webmaster

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    Coronavirus drifts through the air in microscopic droplets – here's the science of infectious aerosols
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    From your lungs into the air around you, aerosols carry coronavirus.
    Peter Dazeley/The Image Bank via Getty Images

    Shelly Miller, University of Colorado Boulder
    During the 1970s when I was growing up in Southern California, the air was so polluted that I was regularly sent home from high school to “shelter in place.” There might not seem to be much in common between staying home due to air pollution and staying home to fight the coronavirus pandemic, but fundamentally, both have a lot to do with aerosols.
    Aerosols are the tiny floating pieces of pollution that make up Los Angeles’ famous smog, the dust particles you see floating in a ray of sunshine and also the small droplets of liquid that escape your mouth when you talk, cough or breathe. These small pieces of floating liquids can contain pieces of the coronavirus and can be major contributor to its spread.
    If you walk outside right now, chances are you will see people wearing masks and practicing social distancing. These actions are in large part meant to prevent people from spreading or inhaling aerosols.
    I am a professor of mechanical engineering and study aerosols and air pollution. The more people understand how aerosols work, the better people can avoid getting or spreading the coronavirus.
    Airborne and everywhere
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    Aerosols are everywhere.
    slobo/E+ via Getty Images


    An aerosol is a clump of small liquid or solid particles floating in the air. They are everywhere in the environment and can be made of anything small enough to float, like smoke, water or coronavirus-carrying saliva.
    When a person coughs, talks or breathes, they throw anywhere between 900 to 300,000 liquid particles from their mouth. These particles range in size from microscopic – a thousandth the width of a hair – up to the size of a grain of fine beach sand. A cough can send them traveling at speeds up to 60 mph.
    Size of the particle and air currents affect how long they will stay in the air. In a still room, tiny particles like smoke can stay airborne for up to eight hours. Larger particles fall out of the air more quickly and land on surfaces after a few minutes.
    By simply being near other people, you are coming into constant contact with aerosols from their mouth. During a pandemic this a little more concerning than normal. But the important question is not do exhaled aerosols exist, rather, how infectious are they?
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    The coronavirus is small and easily transported by airborne particles of saliva.
    fotograzia/Moment via Getty Images


    Aerosols as virus delivery systems
    The new coronavirus, SARS-CoV-2, is tiny, about 0.1 microns - roughly 4 millionths of an inch - in diameter. Aerosols produced by people when they breathe, talk and cough are generally between about 0.7 microns to around 10 microns – completely invisible to the naked eye and easily able to float in air. These particles are mostly biological fluids from people’s mouths and lungs and can contain bits of virus genetic material.
    Researchers don’t yet know how many individual pieces of SARS-CoV-2 an aerosol produced by an infected person’s cough might hold. But in one preprint study, meaning it is currently under peer review, researchers used a model to estimate that a person standing and speaking in a room could release up to 114 infectious doses per hour. The researchers predict that these aerosolized bits of saliva would easily infect other people if this happened in public indoor spaces like a bank, restaurant or pharmacy.
    Another thing to consider is how easy these particles are to inhale. In a recent computer model study, researchers found that people would most likely inhale aerosols from another person that is talking and coughing while sitting less than 6 feet away.
    While this seems bad, the actual process from exposure to infection is a complicated numbers game. Often, viral particles found in aerosols are damaged. A study looking at the flu virus found that only 0.1% of viruses exhaled by a person are actually infectious. The coronavirus also starts to die off once it has left the body, remaining viable in the air for up to three hours. And of course, not every aerosol coming from an infected person will contain the coronavirus. There is a lot of chance involved.
    Public health officials still don’t know whether direct contact, indirect contact through surfaces, or aerosols are the main pathway of transmission for the coronavirus. But everything experts like myself know about aerosols suggests that they could be a major pathway of transmission.
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    Aerosol driven outbreaks have been linked to restaurants, shops and many other public places.
    AP Photo/Vincent Yu


    Evidence of aerosol transmission
    It is almost impossible to study viral transmission in real time, so researchers have turned to environmental sampling and contact tracing to try to study the spread of the coronavirus in aerosols. This research is happening extremely fast and most of it is still under peer review, but these studies offer extremely interesting, if preliminary, information.
    To test the environment, researchers simply sample the air. In Nebraska, scientists found airborne SARS-CoV-2 in a hospital. In China, scientists also found the virus in the air of a number of hospitals as well as a department store.
    But environmental sampling alone cannot prove aerosol transmission. That requires contact tracing.
    One restaurant in Guangzhou, China, was the site of a small outbreak on Jan. 23 and offers direct evidence of aerosol transmission. Researchers believe that there was one infected but asymptomatic person sitting at a table in the restaurant. Because of the air currents circulating in the room due to air conditioning, people sitting at two other tables became infected, likely because of aerosols.
    Overall, the evidence suggests that it is much more risky to be inside than outside. The reason is the lack of airflow. It takes between 15 minutes and three hours for an aerosol to be sucked outside by a ventilation system or float out an open window.
    Another preprint study of outbreaks in Japan suggests that the chances of direct transmission are almost 20 times higher indoors compared to outdoors. In Singapore, researchers traced the first three outbreaks directly to a few shops, a banquet dinner and a church.
    Once outside, these potentially infectious aerosols disappear in the expanse of the atmosphere and are much less of a worry. It is of course possible to catch the virus outside if you are in close contact with a sick person, but this seems very rare. Researchers in China found that only one of 314 outbreaks they examined could be traced back to outdoor contact.
    There has been recent concern over aerosol transmission during running and biking. While the science is still developing on this, it is probably wise to give other bikers or runners a little more room than normal.
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    Wearing masks and social distancing reduce the risk of spreading or inhaling aerosols.
    AP Photo/Gerald Herbert


    How to reduce aerosol transmission
    With all of this knowledge of how aerosols are produced, how they move and the role they play in this pandemic, an obvious question arises: what about masks?
    The Centers for Disease Control and Prevention recommends wearing a face mask in any public setting where social distancing is hard to do. This is because homemade masks probably do a reasonable job of blocking aerosols from leaving your mouth. The evidence generally supports their use and more research is coming to show that masks can be very effective at reducing SARS-CoV-2 in air. Masks aren’t perfect and more studies are currently underway to learn how effective they really are, but taking this small precaution could help slow the pandemic.
    Other than wearing a mask, follow common sense and the guidance of public health officials. Avoid crowded indoor spaces as much as possible. Practice social distancing both inside and outdoors. Wash your hands frequently. All of these things work to prevent the spread of the coronavirus and can help keep you from getting it. There is a significant amount of evidence that COVID-19 is transmitted by the inhalation of airborne particles, but by carefully following the advice of experts, individuals can minimize the risk they pose.
    [Get facts about coronavirus and the latest research. Sign up for The Conversation’s newsletter.][​IMG]
    Shelly Miller, Professor of Mechanical and Environmental Engineering, University of Colorado Boulder
    This article is republished from The Conversation under a Creative Commons license. Read the original article.
     
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  2. I am toxic . . . but I'm not viral

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    Maskaphiles.

    They exist.
     
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  3. dubey $$$$$$$$$$$$$$$$$$$$ big money boyz $$$$$$$$$$$$$$

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    Do you post this in every thread in hopes the term catches on?
     
  4. I am toxic . . . but I'm not viral

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    Definitely.

    I can't claim maskaphobia because prior art.

    But I am hoping that maskaphile is still available.
     
  5. TaLoN Red 5 standing by

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    People who molest masks?
     
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  6. I am toxic . . . but I'm not viral

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    On second thought, maybe I don't want to claim the term.
     
  7. DuklaNation Registered User

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    This was obvious in January for those who followed the story closely. Taiwan knew in December. Our experts couldn't figure it out until late March/early April. Sad.
     
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  8. someguy44 Registered User

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    I posted the virus was aerosolized (basically means airborne) in the mask or no mask thread back in around Feb or early Mar and this one healthcare worker jumped on me saying it wasn't and the public should not be worry about it in public places (even though there were plenty of documented cases and studies that showed it was aersolized. However, because all the articles I posted wasn't peer reviewed, the poster ignored them. Just cause something hasn't been peer reviewed doesn't mean it's not true and should be ignored). Just cause you're a healthcare worker doesn't mean you know what you're talking about (WHO, Dr. Tam, Dr. Bonnie Henry, CDC, etc... have given plenty of misinformation).

    I was warning people to wear masks (dumb people automatically assumed I mean just N95 or surgical masks when it can be DIY masks) the entire time, but people with low or no critical thinking abilities (or people who didn't bother doing any research of their own and just took words at face value from certain health authorities) were saying not to wear masks as they do more harm than good. Of course, now everyone (I hope it's everyone) knows this is is complete bullshit as there's too much mounting evidence for the effectiveness of masks. If people still aren't convinced by the evidence that masks work (either as prevention or protection and for protection, it depends on the type of material use for that mask) against airborne droplets, then they're just in denial or extremely ignorant.

    Anyways, some people (like certain countries' health authorities) are just slow even when the evidence was shown to them prior. They react too slowly, (Canada, US, etc..) and still don't know what proper procedures to take even by now when they should've been more proactive (like Taiwan, Vietnam, S. Korea, etc..) or at least try to copy the models of successful countries. Some countries react a bit faster (like Czechia, Slovakia, etc..). Even countries that react late and plan accordingly (like Austria, Germany, etc..) have started to flatten the curve.

    Here's an excerpt I got off of Peak Prosperity from a fan who sent them this. It shows why masks works (but in this scenario, masks are replaced with pants). Hopefully, those low critical thinkers will get this funny metaphor.

    upload_2020-5-1_18-45-30.png
     
    Last edited: May 1, 2020
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  9. Pez68 Registered User

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    It was intentional, because there weren't even enough masks for healthcare workers.... The information was tailored to suit their agenda at the time.
     
  10. someguy44 Registered User

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    There still aren't enough masks (surgical or N95s). However, this actually backfired on the countries who intentionally misled people into thinking masks don't work because these are the countries with the most cases of infected healthcare/nursing home/care home workers.

    If people can't spread or get infected with the virus, by simply wearing a mask, then people won't need to go to the hospital to infect healthcare workers to begin with.

    They should've done what the Czech Republic did (by asking everyone to make DIY masks) and then making it mandatory to wear in all public places, but our moronic leaders/health authorities instead just outright lied and obviously didn't predict that more healthcare workers would get infected by the public not wearing masks. They plan for days ahead of time instead of months or even just weeks.

    Here's an article about a Boston hospital. Once they made everyone (healthcare workers and patients alike) to mandatory wear masks in the hospital, infections went way way down (well duh).

    Coronavirus Diagnoses In Staff Drop By Half After Boston Hospital Requires Masks For All
     
    Last edited: May 1, 2020
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  11. JacketsFanWest Registered User

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    There are studies which show no benefit:

    Facemasks and similar barriers to prevent respiratory illness such as COVID-19: A rapid systematic review
    The evidence is not sufficiently strong to support widespread use of facemasks as a protective measure against COVID-19.

    Effectiveness of Surgical and Cotton Masks in Blocking SARS–CoV-2: A Controlled Comparison in 4 Patients | Annals of Internal Medicine | American College of Physicians
    In conclusion, both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.
     
  12. Pez68 Registered User

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    Use your damn brain, and your critical thinking skills. When you have a surgical mask on, guess why it gets wet after wearing it for a prolonged period of time? Because it is catching the majority of respiratory droplets when you breathe... Because the majority of respiratory droplets, unless sneezing or coughing, are too large to pass through.

    For every article you find saying the evidence is "not sufficiently strong" there are 10 studies, statements from scientists, doctors, and infectious disease experts that say they DO.

    If masks show no benefit, WHY DO HEALTHCARE WORKERS AND SICK PATIENTS WEAR THEM? For...show? Cosmetic reasons? Peace of mind? They have been giving surgical masks to sick patients for DECADES, because they reduce the chances of spreading the illness.

    Not to mention, absence of evidence, is NOT evidence of absence.

    Once again...RIGHT IN YOUR VERY OWN ARTICLE:

    A study where the individuals they were studying...didn't actually use the mask properly. That's fantastic.

    I'm beginning to believe you don't read a single article you link here start to finish.

    The second link you provided...once again....refers to coughing. Not normal respiratory function.
     
    Last edited: May 1, 2020
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  13. someguy44 Registered User

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    The 2nd article can be ignored because it's a comparison article on the effectiveness of surgical masks vs cotton masks, not an article stating whether face masks/face coverings work or not. It even states within the article that "Whether face masks worn by patients with coronavirus disease 2019 (COVID-19) prevent contamination of the environment is uncertain".

    Your 1st article seems to look at face masks worn through different study methods and the study methods used gave different results (even though it was for the same purpose). The sample size is small and the range went from 6% reduction to 19% reduction. However, this article was posted by Medrxiv on April 6th. They posted another article on April 14th, which states, that based on studies, the effectiveness of mask wearing (by up to 80% reduction rates). It's here: Efficacy of face mask in preventing respiratory virus transmission: a systematic review and meta-analysis

    Anyways, I can find a lot more articles/studies/research on the effectiveness of mask wearing than the "ineffectiveness" of mask wearing. In fact, i just found one from the same Research Institute that you posted the "ineffectiveness" of mask wearing for.

    Better yet, why look at these studies because it's easy to do your own study. Put your hand in front of your mouth. Now spit on it. Feel the saliva on your hand? OK, now put a mask/face covering on. Put your hand in front of your mouth again. Now, spit at your hand again with the mask/face covering on. How much saliva do you feel on your hand now vs the 1st time without the mask/face covering? It is a no brainer that masks/face coverings work to prevent droplets (the majority of them and not necessary all of them) from landing on surfaces or becoming aersolized.

    Anyways, just look at the actual evidence instead of studies from research institutes that change their mind 8 days later. Czech Republic made masks mandatory in public on March 18th. Their number of daily new cases started to remain constant around the 3rd week after mandatory mask wearing. Then, it started going down. Now, they're at double digits for daily new cases. Austria made masks mandatory on Apr 6th. Now, their number of daily new cases is also in the double digits. I don't even have to mention Vietnam or S. Korea or Taiwan as their numbers are either in the single or double digits. Germany just joined the party recently, but it'll take at least 2 to 3 weeks to see the effect, but we are already seeing an effect as they used to have quadruple digits of new daily cases. Now, it's in the triple digits. Turkey only made mask wearing mandatory in shopping places and this is what Austria did in March before they made it mandatory everywhere. I think Turkey needs to follow Austria's example. Anyways, the evidence is clear as day that masks work.
     
    Last edited: May 2, 2020
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