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Dr. Lee Ju-hyung has largely avoided restaurants in recent months, but on the few occasions that he has dined out, he has developed a strange, if sensible habit: pulling out a small anemometer to check air flow.
It’s a precaution he’s been taking since an experiment in June when he and his colleagues recreated conditions at a restaurant in Jeonju, a city in southwestern South Korea, where diners contracted Covid-19 from a visitor from outside the city. city.
Among them was a high school student who became infected with the coronavirus after five minutes of exposure 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.
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The findings raised concerns that the widely accepted standard of 2 meters of social distance may not be enough to keep people safe.
The study, which adds to a growing body of evidence on airborne transmission of the virus, highlighted how South Korea’s meticulous and often invasive contact tracing regimen has allowed researchers to closely follow how the virus moves through of populations.
“In this outbreak, the distances between the contactor and infected people were … longer than the generally accepted 2-meter droplet transmission range,” the study authors wrote.
ED JONES / Getty Images
A recent study has found that the widely accepted standard of 2m of social distance may not be far enough to keep people safe from coronavirus.
“The guidelines on quarantine and epidemiological investigation must be updated to reflect these factors for the control and prevention of Covid-19.”
People wearing face masks walk past a coronavirus safety ad advising of an enhanced social distancing campaign in Seoul.
KJ Seung, an infectious disease expert and head of strategy and policy for the Massachusetts Covid response at the nonprofit Partners in Health, said the study was a reminder of the risk of indoor transmission as many nations brace themselves. for the winter.
The official definition of “close contact” – 15 minutes, within 2 m – is not infallible. In his work at the Massachusetts contact tracing program, he said, business owners and school administrators have set themselves to the standard of “close contact,” thinking that only 14 minutes of exposure, or spending hours in the same room at a distance greater than 2m, it is safe.
“There is a real misconception about this in the public.” said Seung, who was not involved in the South Korean study.
“They’re thinking, if I’m not a close contact, I’ll be magically protected.”
Seung said the study pointed to the need for contact trackers around the world to expand the network for people who have potentially been infected and to alert people at lower risk that they may have been exposed.
Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who studies airborne virus transmission, said the five-minute window in which the student, identified in the study as “A,” was infected was remarkable because the The drop was large enough to carry a viral load, but small enough to travel 6 m through the air.
“‘A’ had to receive a large dose in just five minutes, provided by larger aerosols, probably around 50 microns,” he said.
“Large aerosols or small droplets overlapping in that gray area can transmit disease over a meter or two if you have strong airflow.”
The South Korean study began with a mystery. When a high school senior in Jeonju tested positive for the coronavirus on June 17, epidemiologists were puzzled that the city had not had a case of Covid-19 in two months.
North Jeolla Province, where Jeonju is located, hadn’t had one for a month. The girl had not traveled outside the region in recent weeks and had largely gone from home to school and vice versa.
Contact trackers turned to the country’s Epidemic Research Support System, a digital platform introduced in South Korea amid the pandemic that allows researchers to access cell phone location information and credit card data from infected people in as little as 10 minutes.
Cell phone GPS data revealed that the student briefly overlapped with another known coronavirus patient from an entirely different city and province, a door-to-door saleswoman who had visited Jeonju.
Their connection was a restaurant on the first floor on the afternoon of June 12, for just five minutes.
Authorities in Daejeon city, where the door-to-door saleswoman was visiting, said the woman did not tell contact trackers that she had visited Jeonju, an hour’s drive away, where her company held a meeting with 80 people on the 6th floor of the building with the restaurant.
Lee, a professor at Jeonbuk National University School of Medicine who has also been helping local authorities conduct epidemiological investigations, went to the restaurant and was surprised at how far apart the two had been sitting.
CCTV footage showed the two never spoke or touched any surface in common: door handles, cups or silverware.
By the swing of a lamp, he could tell that the ceiling air conditioning unit was on at the moment. Lee and his team recreated the conditions in the restaurant (the researchers sat at the tables as stand-ins) and measured airflow.
The high school student and a third diner who was infected had been sitting directly next to the flow of air from an air conditioner; other diners who had their backs to the airflow were not infected.
Using genome sequencing, the team confirmed that the genomic types of viruses of the three patients matched.
“Unbelievably, despite sitting far away, the airflow came down the wall and created a valley of wind. People who were on that line were infected, ”Lee said.
“We concluded that it was a transmission by droplets, and beyond two meters.”
The pattern of infection in the restaurant showed it was due to transmission via droplets landing on the face rather than aerosols, which are inhaled, said Marr, the Virginia Tech professor who was not involved in the study.
The air speed measured in the restaurant, which had no windows or ventilation system, was about one meter per second, the equivalent of a fan.
“Eating inside a restaurant is one of the riskiest things you can do in a pandemic,” he said.
“Even if there is distancing, as this and other studies show, distancing is not enough.”
The study was published at a time when South Korea, like many other countries, is on the edge amid a new wave of Covid-19 infections, with daily case rates hovering around 600 in recent days.
Seoul, the capital, began this week requiring restaurants to close at 9 p.m., limiting coffee shops to takeout only and forcing clubs and karaoke bars to close.
The research echoed findings from a July study in Guangzhou, China, which looked at infections among three families who dined at a restaurant along the air-conditioning flow at tables that were a meter apart, overlapping for about one hour.
Ten of the diners tested positive for the coronavirus.
Contact trackers in South Korea drew a similar map of a large outbreak at a Starbucks in Paju in August, when 27 people were infected by a woman sitting under an air conditioning unit on the second-floor ceiling.
Partners in Health’s Seung said that by tracing infection routes, epidemiological researchers in South Korea had helped researchers around the world better understand the spread of the coronavirus.
“I showed it to my team doing contact tracing in Massachusetts, and they were blown away,” Seung said.
“We know how difficult it is to do something like that, it’s impressive.”
– Los Angeles Times
