Thread by @AbraarKaran

1/ It's difficult to study #SARSCoV2 transmission in the real world bc of many confounders

In our study of hospital roommates, we studied this in a relatively controlled setting

We found that the virus transmits efficiently beyond 6 feet & despite a curtain in between roommates

2/ We were examining a number of cases that turned positive but whose initial tests were negative (so early incubation period) so they were roomed with other patients in shared rooms

This allowed us to explore a window into exposure when index cases are most infectious

3/ We found that for those with cycle threshold values <=21 (meaning high viral load), 11/18 transmitted to their roommate (61%)

Roommates are 7 feet apart (head to head in bed) with a solid curtain in between

If transmission was primarily droplets, we wouldn't expect this

4/ Furthermore, not all of the exposed roommates had serial testing after discharge (despite attempts to reach them)

This means some of those patients actually could have been infected but not detected (and possibly indicates a higher transmission rate than what we found)

5/ Median time from exposure to infection in roommates was 5 days, which would fit more in line with transmission from roommate than otherwise

As part of cluster tracing, nurses & staff etc are also tested which helped further narrow the roommate as the most likely source

6/ I don't want to bury the punch line here but...here is the big problem.

Cases are most infectious before or right when they are showing symptoms

11/12 transmission events in our study were from people with CT values <=21 (91.7%)

7/ This again fits with the idea that transmission is happening in a short window

when it is happening, it is happening *very effectively*-- airborne transmission to those around

despite 6 feet of distance

despite a solid curtain in between them

despite excellent ventilation

8/ We couldn't assess mask use in this study.

But in my anecdotal experience working at BWH for all of last year seeing many patients, consistent masking of patients was a coin flip at best

Let's then apply some of these ideas to the community setting or people's homes...

9/ Community- crowded, indoor spaces with much poorer ventilation than hospital rooms.

I'm thinking of restaurant kitchens/ factory workspaces/ conference rooms w/ big groups around the table etc

People's homes- likely no masking, but bringing back infection from community

10/ Also then sleeping next to spouse without knowing you are infected

Of course, these scenarios were most concerning before we had vaccines-- with vaccines, we know that both transmission is reduced; & disease is reduced as well

11/ But-- many places around the world remain unvaccinated

And many places seem to still focus on droplets/fomites as the primary modes of spread, at least by the interventions they are focused on such as cloth masks or wiping surfaces.

Focus needs to be on the air

12/ The principles of #SARSCoV2 transmission are the same (arguably worse/amplified with Delta variant)

Transmission must be thought of on a continuum of risk, not a dichotomy that is oversimplifying it (like 6 feet/15 minutes)

This can make it hard for people to make decisions

13/
More time together
Less distance apart
Crappier mask on
Poorer ventilation
Unvaccinated**
Higher the viral load

Higher risk of transmission

Age, comorbidities, viral inoculum, Delta variant, unvaccinated, lack of prior infection

Higher risk of disease

#covid19