Thread by @DrEricDing

JUST IN—CDC is changes how “close contact” is defined. Instead of previously defining “close contact” as >=15 *consecutive* minutes w/in 6 feet of #COVID19 case, it’s now w/in 6 feet of an infected case for >=15 minutes cumulatively over 24-hours. Huge. 🧵 washingtonpost.com/health/2020/10…

2) “The change by The Centers for Disease Control and Prevention is likely to have its biggest impact in schools, workplaces and other group settings where people are in contact with others for long periods of time.”

3) “The updated guidance is based on new evidence: CDC and Vermont health officials discovered infection of a 20-year-old prison employee who interacted with individuals who later tested positive for the virus after 22 interactions totaling 17 minutes during an 8-hour shift.”

4) “Available data suggests that at least one of the asymptomatic [infectious detainees] transmitted” the virus during these brief encounters, the report said.”

5) Bottomline: the old definition of within 6 feet for 15 consecutive minutes was too limited. Cumulative aggregate exposure can lead to infection.

I still don’t know if the 15 minutes and 6 feet rule is sufficient given what we know about airborne transmission via aerosols.

6) distance isn’t what always matter. Studies indicates that coronavirus could be persistent and stable up to 16 hours in stagnant air. Typical air exchange every 20 min to 4 hrs, depending on ventilation. #COVID19

7) Here is the link to the latest Vermont prison outbreak that was because of 17 aggregate minutes of intermittent visits that led to the infection of the prison guard from asymptomatic inmates. This virus is just that subtle and perniciously persistent.

https://twitter.com/alinouriphd/status/1319013745683816449

8) And not to spoil anyone’s day, but NZ contract tracing says 3 minutes of casual exposure can lead to an infection. NZ cases are rare, so unlikely any other source.

https://twitter.com/DrEricDing/status/1319026171674243072