Wednesday, Sept. 9The word for today is “aerosol." An aerosol is a suspension of droplets in air. In this case, of course, we are talking about small droplets, or aerosols. Most of the spread of COVID-19 is aerosol transmission, and not fomite, or large droplet. Fomite means surfaces are contaminated. You can have fomite transmission when you touch a fomite surface, and then touch a mucus membrane like your mouth. Large droplets are those respiratory droplets with a range of about six feet before they fall to the ground. Small droplets are aerosols, and there is no range.You read that correctly, there is no range. The six-foot rule is dead. What? Blasphemy? Not really.Infectious disease epidemiologists have known this for some time. Aerosol transmission of COVID-19 depends critically on ventilation. Let’s define that as the number of changes of indoor air with fresh outdoor air. But in calm air, transmission will still drop off with distance as virus concentration lowers. With low enough ventilation, and enough time, you can become infected at large distances. In a Starbucks in South Korea, 66 cases were linked to one person, talking, maskless, sitting under the air conditioning for two hours. It is thought she was the sole source for 66 infections, because she sat next to the air conditioner intake. Here is a link to that story from Business Insider:https://www.businessinsider.in/science/news/56-people-got-the-coronavirus-at-a-starbucks-in-south-korea-the-only-people-who-didnt-were-employees-wearing-masks-/articleshow/77727075.cmsHow does this change things? For starters, the indoor air ventilation is the critical variable in the ability of COVID-19 to spread. There is a neat trick you can play. You can use a CO2 monitor to assess air quality. It will be a balance between human respiration and ventilation. If C02 stays low, you are good.What about fighting COVID-19 via ventilation? Absolutely. Open those windows. Go outside. Something you can do inside is use HEPA filters at a MERV-13 rating. These filters will remove the droplets. Don’t get confused and think you need to remove virions (diameter 40 nanometers), because you do not. You only need to remove those small droplets (1-50 microns) and you will also remove the virions. Such technology is mature and ready to deploy today.And the third takeaway from aerosol transmission is: Wear masks especially in closed indoor settings where transmission is highest.Today’s blog is not about things I have done or studied. Rather, I will refer you to the excellent resources written by Professor Jose-Luis Jimenez, a professor of chemistry whose specialty is aerosols. He is on a mission to inform the public about how aerosol knowledge can inform us about COVID-19, and he has a great FAQ online. His twitter handle is https://twitter.com/jljcolorado.I highly recommend you read his FAQ for more knowledge about aerosols:https://docs.google.com/document/d/1fB5pysccOHvxphpTmCG_TGdytavMmc1cUumn8m0pwzo/edit#heading=h.sn3wgajjrq1cBack tomorrow with more data science as we explore “backdating” of new reports and the implications it has for our ability to contact trace.
The COVID Report with David Blake: What is aerosol transmission?
