Thread by @linseymarr

Why the big debate over airborne transmission? Exchanges with @OlabisiLab Matthew Meselson @kprather88 over the weekend helped me crystallize some thoughts about the disconnect. /1

Traditional discussion about transmission routes centers around operational definitions in infection control and prevention in hospitals. There are "airborne" diseases/precautions and "droplet" diseases/precautions. /2

The problem is that we have been trying to impose these operational definitions on the actual mechanisms of transmission and apply them in community (non-hospital) settings. /3

The mental model, then, is that airborne transmission only matters at long range, as shown in this figure, and that if transmission occurs at close range, it's due to large droplets. But how do the aerosols get to long range? /4

This figure from our paper on myths about transmission (journalofhospitalinfection.com/article/S0195-…) shows a more realistic version of what's happening. Aerosols are more concentrated at close range. /5

Why do "droplet" precautions mostly work in hospitals? Hospitals have a narrower range of host and environmental factors that affect transmission. Ventilation is usually good. People aren't singing, exercising, spending hours in a room with lots of people. People wear masks. /6

Under these conditions "droplet" precautions mostly work because there are layered interventions that also address aerosols. But these precautions aren't always enough, as seen in some studies (acpjournals.org/doi/full/10.73…, academic.oup.com/ofid/article/8…). /7

At the same time, we don't necessarily need full "airborne" precautions with airborne infection isolation rooms because SARS-CoV-2 is not as easily transmissible as measles. But hospitals are boxed in by the operational definitions. /8

For the general public, the clearest way to convey how the virus is transmitted is to call it airborne. Hospitals should not have a monopoly on the term. We live with a different meaning of the word "chart" in hospitals. /9

@meganmolteni describes Yuguo Li's take (wired.com/story/the-teen…): airborne transmission is both more complicated and less scary than once believed. /10

Hospitals can maintain their definitions. Meanwhile, we should transition to talking about transmission by actual mechanisms: inhalation of aerosols, spray/impaction of large droplets, and touching contaminated surfaces, as suggested by Yuguo Li @don_milton and me. /11

These definitions better explain how the virus is actually transferred between people and correspond to different interventions, like high-performance masks and ventilation, distancing and face shields, hygiene and cleaning, respectively. /12

Let's get to it, @WHO @DrTedros @doctorsoumya @mvankerkhove. We can end this pandemic more quickly and be better prepared next time around. /13