As a non-epidemiologist, this was perhaps the most enlightening article I’ve read on SARS-CoV-2 by @zeynep (h/t: @malia_ailam)

I will summarize the article and highlight key points down : https://www.theatlantic.com/health/archive/2020/09/k-overlooked-variable-driving-pandemic/616548/

Multiple studies have suggested that as few as 10-20% of infected people may be responsible for as much as 80-90% of transmission. Some super spread and others barely transmit it.

Super-spreading clusters almost overwhelmingly occur in poorly ventilated indoor environments where many people get together for extended period of time (eg: weddings, churches, choirs, restaurants, bars) - and especially when there is loud talking or singing without masks.

“For super-spreading events to occur, multiple things have to be happening at the same time, and the risk is not equal in every setting and activity.”

“prolonged contact, poor ventilation, highly infectious person, crowding” are the key elements for a super-spreader event.
6ft guideline may not be appropriate indoors with poor ventilation because SARS-CoV-2 can travel through the air.

Because of overdispersion, forward contact tracing is not necessarily the most effective thing to do with limited resources. Instead, first, we should try to work backwards to see who first infected the person.

Most people will have been infected by someone who also infected other people. Only a small % of people infect a large number of people. Whereas most infect 0/1 extra person, ending the transmission chain.

The most important point:

With retrospective contact tracing, find the person who infected the person and then trace forward. Will find a lot more cases vs forward-tracing, which will only identify potential exposures (many of which likely will not happen).

“forward tracing alone can, on avg, identify at most the mean # of secondary infections (i.e. R)”

“backward tracing increases this max # of traceable individuals by a factor of 2-3, as index cases are more likely to come from clusters than a case is to generate a cluster.”

Adding to this thread another huge study (h/t: @DFisman) that adds to this: https://www.latimes.com/world-nation/story/2020-09-30/largest-covid-19-transmission-study-highlights-super-spreaders

A team of Indian and U.S. researchers examined data from 575,071 individuals who were tested after coming into contact with 84,965 people with confirmed cases of COVID-19. Average of 7 contacts/case, and a cohort more than 10 times larger than in a previous study from South Korea

“Laxminarayan and his colleagues found that just 8% of people with COVID-19 accounted for 60% of the new infections observed among the contacts. Meanwhile, 7 out of 10 COVID-19 patients were not linked to any new cases.”