Thread by @maryaalexand1

Time for a thread on: What Do We Know About Outdoor Transmission of Delta? @linseymarr @Daltmann10 @LongCovidKids @Ayjchan @VirusesImmunity @dgurdasani1 @ScottGottliebMD @kprather88 @DrEricDing @IndependentSage @michaelzlin @segal_eran @ashishkjha @Bob_Wachter @PeterHotez @CDCgov

1. Delta behavior indoors & outdoors: they saw fleeting proximity transmission in the Bondi Junction outbreak. Only needed 5-10 seconds proximity or 1-3 inhalations if briefly within 2 ft of someone else.

These kinds of transmission occurred when just “brushing past” someone & was well documented for indoor cases by genomic testing and CCTV. They also had a case of a woman sitting outdoors at a cafe who was infected by a man who visited the cafe when she was not inside.

This first potential documented case of outdoor transmission with Delta was also confirmed by CCTV and genomic testing. Here’s the three clips of evidence about this case: Woman outdoors at cafe is case #3 in this video, run down of initial outbreak:

https://twitter.com/DrEricDing/status/1406779894785351688?s=20

More about her here:

https://twitter.com/drericding/status/1406784126842245121?s=21

More here: she was sitting outside of the Belle Cafe while the infected cab driver was inside the cafe. What they saw on security cameras is that they never really came into contact but he did transmit it to her.

https://twitter.com/drericding/status/1406786465531584512?s=21

2. TRANSMISSION OF DELTA AT OUTDOOR STADIA

Very likely outdoor transmission of Delta, multiple occurrences, at 2 stadiums (MCG & AAMI) as shown by contact tracing, “transmission at stadia absolutely occurs” per Brett Sutton, Chief Health Officer, Victoria. @VictorianCHO

Outdoor transmission may be particularly occurring “at pinch points outdoors” (where you are more likely to be forced to be within 6 ft or less of someone). For example, pinch points occur when entering and exiting areas of the stadium.

Lower risk of transmission than indoors but not insignificant. "We think there's been outdoor transmission. It's lower risk [than indoors] but it happens." -Brett Sutton, Chief Health Officer, Victoria

https://twitter.com/drpieterpeach/status/1416979038862598148?s=21

3. Dr. Lynsey Marr, Professor of Civil & Environmental Engineering @ Virginia Tech (studies airborne virus transmission) agrees:

“15 minutes becomes just a few seconds” to become infected
“if close to someone and in their respiratory plume”
“outdoors does become more risky”

“Let’s say you had to spend 15 minutes with an infected person in a closed room before you would be exposed to enough virus to get sick. Now we’re talking about 1,000 times that potentially,” says Dr. Marr. “So that 15 minutes becomes just a few seconds.” @linseymarr

“Many people have long considered outdoor activities safe but scientists say it makes sense to rethink that assumption in certain situations. Delta increases the risk of outdoor transmission—especially for unvaccinated people, scientists say.”

“Outdoors does become more risky,” says Dr. Marr. If you are close to someone and in their respiratory plume—the air released in a breath—it may be possible to become infected, she says. The risks increase outdoors in more crowded settings, such as a concert or a baseball game.”

“She does recommend even vaccinated people wear a mask outside in crowded settings.”

This could include stadia, amusement parks, schools (unless kids are supervised to stay 6 feet apart or more), concerts, outdoor church settings that don’t maintain spacing of 6 ft or more, etc.

Outdoor structures: “Outdoor risk increases if you’re in a wedding tent or structure where 3 sides are enclosed. “I don’t classify that as outdoors,” says Dr. Volckens. “The air exchange is limited. The air is more confined so the accumulation of this exhaled air is rebreathed.”

wsj.com/articles/the-d…