5/ c) Aerosols: don’t fall to ground quickly unlike drops, stay in the air tens of sec to hrs (depend on size). Infect by inhalation (or deposition onto eyes). Substantial evidence it happens (https://academic.oup.com/cid/article/doi/10.1093/cid/ciaa939/5867798 …), not 100% proof, @WHO resists.
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6/ So 2 main players: drops & aerosols. 2 pieces of evidence suggest relative importance: - Pandemic driven by superspreading events (eg https://www.nytimes.com/2020/06/30/science/how-coronavirus-spreads.html …). Easy to explain w/ aerosols. Harder w/ drops. Transmission requires “prolongued close contact” (PCC).
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7/ Need PCC with lots of ppl in a location. E.g. Skagit Choir (we investigated), fixed singing positions w/ 0-2 people within 6 ft in landing area of drops. A couple of 10 min breaks. Could index case “spit” drops on 53 ppl in such short breaks? No time for PCC!
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8/ Guangzhou restaurant, buses, other cases. “Contorsionist thinking” (B. Nazaroff) required to explain w/o aerosols - Note that when face-to-face, majority of infection likely through aerosols, much more concentrated right in front of person:https://www.sciencedirect.com/science/article/abs/pii/S0360132320302183 …
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9/ -There is PCC both indoors & outdoors. Drops are ballistic, no time for dilution or UV to remove virus, don’t care indoors or outdoors, should be similar. Aerosols are carried by the wind, incredible dilution, more time for UV to destroy virus (very quick).
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10/ Run Skagit choir case in aerosol transmission estimator (https://tinyurl.com/covid-estimator “choir” sheet), reproduces infection rate. Now move exact choir outdoors (“outdoors” sheet), infection drops from 83% to 0.4%.
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11/ Real-world: "The vast majority of transmission seems to be through close contact with an infected individual, primarily in an indoor setting." (CBC article above). Only aerosols can explain this.
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12/ Conclusion: for the first time, I am ready to say publicly that my *guess* is that the majority (>50%) of the spread is through aerosols. Pls comment w/ your take.
@linseymarr@ShellyMBoulder@CathNoakes@Don_Milton@SaskiaPopescu@angie_rasmussen@eliowa@GidMK30 replies 107 retweets 407 likesShow this thread -
Replying to @jljcolorado @linseymarr and
Well, some thoughts I guess. Firstly, as the WHO points out, all of the superspreading events thus far ~could~ be explained adequately with fomites and droplet spreadpic.twitter.com/u5rpguT8sL
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Replying to @GidMK @jljcolorado and
Droplets don't just require people to *spit*, this is a mischaracterization. Fomites, in particular, have been demonstrated to spread respiratory disease, including things like paper being passed around (an obvious possibility in a choir!)https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1828811/ …
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Broadly speaking, I think this is where the basic scientists and epidemiologists are coming into conflict. Saying "this is how aerosols work!" is meaningless if you don't engage in contact tracing investigations looking at how the virus ~actually spreads~
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Replying to @GidMK @jljcolorado and
For example, if there was substantial aerosol spread from particles hanging around in the air, we'd expect a large proportion of cases that cannot be traced back to a specific case Instead, we find exactly the opposite!
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Replying to @GidMK @jljcolorado and
In places with adequate testing/contact tracing, the vast majority (95%+) of cases can be traced back to specific contacts This is a really important point
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