Korean Study: Indoor SARS-CoV-2 Transmission from 21 Feet Away in Just 5 Minutes
Zeynep Tufekci reports on a small study from Korea that has big implications on how we think about transmission of SARS-CoV-2. Scientists traced two cases back to a restaurant and discovered that transmission had occurred over quite a long distance in a very short period of time.
If you just want the results: one person (Case B) infected two other people (case A and C) from a distance away of 6.5 meters (~21 feet) and 4.8m (~15 feet). Case B and case A overlapped for just five minutes at quite a distance away. These people were well beyond the current 6 feet / 2 meter guidelines of CDC and much further than the current 3 feet / one meter distance advocated by the WHO. And they still transmitted the virus.
As Tufekci goes on to explain, the way they figured this out was quite clever: they contact traced, used CCTV footage from the restaurant, recreated the airflow in the space, and verified the transmission chain with genome sequencing. Here’s a seating diagram that shows the airflow in relation to where everyone was sitting:
Someone infecting another person 21 feet away in only five minutes while others who were closer for longer went uninfected is an extraordinary claim and they absolutely nailed it down. As Sherlock Holmes said: “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” And the truth is that in some cases, the recommended 6 feet of distance indoors is not sufficient when people aren’t wearing masks. Airflow matters. Ventilation matters. Which way people are facing matters. How much people are talking/laughing/yelling/singing matters. Masks matter. 6 feet of distance does not confer magical protection. All that can make it tough to figure out if certain situations are safe or not, but for me it’s an easy calculation: absolutely no time indoors with other people not wearing masks. Period. As Tufekci concludes:
I think there are three broad lessons here. One, small data can be extremely illuminating. Two, air flow and talking seem to matter a great deal. Three, sadly, indoor dining and any activity where people are either singing or huffing and puffing (like a gym) indoors, especially with poor ventilation, clearly remains high risk.
Read her whole post — as she says, it’s “perhaps one of the finest examples of shoe-leather epidemiology I’ve seen since the beginning of the pandemic”.
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