Infected after 5 minutes, from 20 feet away: South Korea study shows coronavirus’ spread indoors
SEOUL — Dr. Lee Ju-hyung has largely avoided restaurants in recent months, but on the few occasions he’s dined out, he’s developed a strange, if sensible, habit: whipping out a small anemometer to check the airflow.
It’s a precaution he has been taking since a June experiment in which he and colleagues re-created the conditions at a restaurant in Jeonju, a city in southwestern South Korea, where diners contracted the coronavirus from an out-of-town visitor. Among them was a high school student who became infected after five minutes of exposure from more than 20 feet away.
The results of the study, for which Lee and other epidemiologists enlisted the help of an engineer who specializes in aerodynamics, were published last week in the Journal of Korean Medical Science.
The conclusions raised concerns that the widely accepted standard of six feet of social distance may not be far enough to keep people safe.
The study — adding to a growing body of evidence on airborne transmission of the virus — highlighted how South Korea’s meticulous and often invasive contact tracing regime has enabled researchers to closely track how the virus moves through populations. “In this outbreak, the distances between infector and infected persons were ... farther than the generally accepted 2 meter [6.6-foot] droplet transmission range,” the study’s authors wrote. “The guidelines on quarantine and epidemiological investigation must be updated to reflect these factors for control and prevention of COVID-19.”
People wearing face masks walk under a banner emphasizing an enhanced social distancing campaign in front of Seoul City Hall. The banner reads: “We have to stop before COVID-19 stops everything.”
KJ Seung, an infectious disease expert and chief of strategy and policy for the nonprofit Partners in Health’s Massachusetts COVID response, said the study was a reminder of the risk of indoor transmission as many nations hunker down for the winter. The official definition of a “close contact” — 15 minutes, within six feet — isn’t foolproof.
In his work on Massachusetts’ contact tracing program, he said, business owners and school administrators have fixated on the “close contact” standard, thinking just 14 minutes of exposure, or spending hours in the same room at a distance farther than six feet, is safe. “There’s a real misconception about this in the public,” said Seung, who was not involved in the South Korea study. “They’re thinking, if I’m not a close contact, I will magically be protected.” Seung said the study pointed to the need for contact tracers around the world to widen the net in looking for people who had potentially been infected and to alert people at lower risk that they may have been exposed.
Linsey Marr, a civil and environmental engineering professor at Virginia Tech who studies the transmission of viruses in the air, said the five-minute window in which the student, identified in the study as “A,” was infected was notable because the
droplet was large enough to carry a viral load, but small enough to travel 20 feet through the air.