Your Update suggests you’ve realized this by now, but your confusion seems to be stemming from not understanding the difference between _droplets_ (large particles, fall to ground within seconds) and _aerosols_ (small particles, can float for 10s of minutes). The reason why there is an emphasis on staying 6 feet away and being careful of touching contaminated surfaces, but not an emphasis on ventilation, is because it is thought that SARS-CoV2 is mostly expelled as droplets and not as aerosols. The purported contraction disappears in this light.
Droplets are larger particles that fall to the ground within seconds, but can be expelled up to ~6 ft / 2 meters by coughing and sneezing. Droplets can also be expelled by talking. Droplets containing the virus can directly land in the face of another person, hence the recommendations to stay 6 ft away. They can also land on surfaces, whence these surfaces become “fomites” that can pass the virus to other people via touching.
Aerosols are smaller particles that can remain in the air for longer periods and potentially be moved around by ventilation systems. I think aerosolized virus can in principle be expelled by an infected person but based on the reporting and scientist interviews I’ve heard (admittedly mostly on This Week in Virology), my understanding is that experts think that SARS-CoV2 is mostly being expelled and hence spread by droplets and not aerosols. Aerosolization might be more important in some situations, such as by certain types of high energy toilets acting on fecally shed virus, but perhaps more important when patients are intubated in hospitals to go on ventilators. And aerosolized virus might turn out to be more common and play a more important role in SARS-CoV2 transmission than experts currently think and so it’s perhaps still something to be aware of as an individual and no doubt warrants more research.
Regarding how long aerosols remain in the air...I am not familiar with the retracted article you mentioned, but the NYT reported that the authors of the now famous aerosol + surface stability study said that aerosols of SARS-CoV2 stayed in the air for 1⁄2 an hour. The paper itself doesn’t contain this 1⁄2 hour number, and the authors needed to use a rotating drum to keep the virus floating for 3 hours. My understanding is that the 1⁄2 hour floating time has nothing to do with SARS-CoV2 itself and is just a property of physics and the size of the particles. Which is still a long time. But the question is whether significant aerosolized virus is being produced by infected people in normal circumstances. In the above paper, the authors used a nebulizer to aerosolize live virus, it didn’t happen naturally.
Note: I have not reviewed the scientific evidence that the CDC and other experts have used to draw the conclusion that droplets and contaminated surfaces are more important than aerosols for SARS-CoV2 transmission.
Thanks! Yes, I think we’re mostly on the same page, except my feeling that avoiding inhaled droplets is probably more important than avoiding touching your face. I still think that the public-health messaging I’ve seen is somewhat misdirected, and that all the celebrities and informational signs that say “wash your hands” or “don’t shake hands” should instead more often say “don’t have face-to-face conversations” and “if you talk to someone, you’re spitting on them” and “cover your cough”. The 2 meter rule is good, but I think it hasn’t been communicated why that’s important, if no one is coughing. Likewise, we all know that you should especially wash your hands after touching a contaminated surface. But conventional wisdom is that a contaminated surface is one that a sick person has touched. Do people realize that a contaminated surface is also one that a sick person has talked near? I, for one, did not connect those dots that until just now.
Your Update suggests you’ve realized this by now, but your confusion seems to be stemming from not understanding the difference between _droplets_ (large particles, fall to ground within seconds) and _aerosols_ (small particles, can float for 10s of minutes). The reason why there is an emphasis on staying 6 feet away and being careful of touching contaminated surfaces, but not an emphasis on ventilation, is because it is thought that SARS-CoV2 is mostly expelled as droplets and not as aerosols. The purported contraction disappears in this light.
Droplets are larger particles that fall to the ground within seconds, but can be expelled up to ~6 ft / 2 meters by coughing and sneezing. Droplets can also be expelled by talking. Droplets containing the virus can directly land in the face of another person, hence the recommendations to stay 6 ft away. They can also land on surfaces, whence these surfaces become “fomites” that can pass the virus to other people via touching.
Aerosols are smaller particles that can remain in the air for longer periods and potentially be moved around by ventilation systems. I think aerosolized virus can in principle be expelled by an infected person but based on the reporting and scientist interviews I’ve heard (admittedly mostly on This Week in Virology), my understanding is that experts think that SARS-CoV2 is mostly being expelled and hence spread by droplets and not aerosols. Aerosolization might be more important in some situations, such as by certain types of high energy toilets acting on fecally shed virus, but perhaps more important when patients are intubated in hospitals to go on ventilators. And aerosolized virus might turn out to be more common and play a more important role in SARS-CoV2 transmission than experts currently think and so it’s perhaps still something to be aware of as an individual and no doubt warrants more research.
Regarding how long aerosols remain in the air...I am not familiar with the retracted article you mentioned, but the NYT reported that the authors of the now famous aerosol + surface stability study said that aerosols of SARS-CoV2 stayed in the air for 1⁄2 an hour. The paper itself doesn’t contain this 1⁄2 hour number, and the authors needed to use a rotating drum to keep the virus floating for 3 hours. My understanding is that the 1⁄2 hour floating time has nothing to do with SARS-CoV2 itself and is just a property of physics and the size of the particles. Which is still a long time. But the question is whether significant aerosolized virus is being produced by infected people in normal circumstances. In the above paper, the authors used a nebulizer to aerosolize live virus, it didn’t happen naturally.
Note: I have not reviewed the scientific evidence that the CDC and other experts have used to draw the conclusion that droplets and contaminated surfaces are more important than aerosols for SARS-CoV2 transmission.
Thanks! Yes, I think we’re mostly on the same page, except my feeling that avoiding inhaled droplets is probably more important than avoiding touching your face. I still think that the public-health messaging I’ve seen is somewhat misdirected, and that all the celebrities and informational signs that say “wash your hands” or “don’t shake hands” should instead more often say “don’t have face-to-face conversations” and “if you talk to someone, you’re spitting on them” and “cover your cough”. The 2 meter rule is good, but I think it hasn’t been communicated why that’s important, if no one is coughing. Likewise, we all know that you should especially wash your hands after touching a contaminated surface. But conventional wisdom is that a contaminated surface is one that a sick person has touched. Do people realize that a contaminated surface is also one that a sick person has talked near? I, for one, did not connect those dots that until just now.
Just a note that there still seems to be disagreement and a lot of uncertainty about aerosol transmission https://www.nature.com/articles/d41586-020-00974-w