Thread by @jljcolorado

@MackayIM @Lucas_Bolivian Because... of Dr. Charles Chapin and his 1910 book: archive.org/details/source…
- In that book Chapin proposed contact infection, a hugely important advance
- He realized importance of infection in close proximity, and usefulness of social distancing to reduce infection

@MackayIM @Lucas_Bolivian - Correctly concludes that ease of infection in close prox. must be due to Flugge's "sprayborne droplets" or "airborne" aerosols
- About airborne: “In air infection, it becomes evident that our knowledge is far too scanty, and that the available evidence is far from conclusive”

@MackayIM @Lucas_Bolivian - But this leaves him with a problem: "It is impossible to teach people to avoid contact infection while they are firmly convinced that the air is the chief vehicle of infection”

@MackayIM @Lucas_Bolivian So: “There is no evidence that [air infection] is is an appreciable factor in the maintenance of most of our common contagious diseases. We are warranted, then, in discarding it as a working hypothesis, and devoting our chief attention to the prevention of contact infection.”

@MackayIM @Lucas_Bolivian - I.e. he turned absence of evidence into evidence of absence
- due to importance of contact infection, this becomes paradigm of epidemiology and ID... till 2020

@MackayIM @Lucas_Bolivian - Despite fierce resistance, Wells and Riley and others manage to show that some diseases are airborne. The most contagious, since easiest to demonstrate (in a very difficult subject)
- Leading to artifact of history being confused w/ law of nature (airborne must be v contagious)

@MackayIM @Lucas_Bolivian When we met with @WHO's personnel and IPC committee in April 6, they were all "Chapinistas."

Little evidence for droplets of surfaces, but aerosols were an extraordinary claim, that required extraordinary evidence. Same level of evidence as for droplets nowhere near enough!

@MackayIM @Lucas_Bolivian @WHO All of that said, I do think that large droplets can transmit disease, if someone coughs or sneezes in someone else's face and scores a "hit". So we should give them *some* attention. But we have to put them on their rightful place, relative to the risk.