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Cord Hurn
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 Posted: Mon Jan 11, 2021 8:30 am Post subject: |
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Thank goodness we're not on some kind of tight timetable to figure all of this out!  |
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Wosbald
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| Posted: Sun Jan 17, 2021 9:52 pm Post subject: |
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+JMJ+
Infected after 5 minutes, from 20 feet away: South Korea study shows coronavirus’ spread indoors [In-Depth]
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An outdoor dining set-up with hand sanitizers and stuffed bears to enforce social distancing in Seoul. (Lee Jin-man / Associated Press)
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.”(Ahn Young-joon / Associated Press)
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.
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Lee, a professor at the Jeonbuk National University Medical School who has also been helping local authorities carry out epidemiological investigations, went to the restaurant and was surprised by how far the two [case studies] had been sitting [at the restaurant implicated at the center of the study]. CCTV recordings showed the two never spoke, or touched any surfaces in common — door handles, cups or cutlery. From the sway of a light fixture, he could tell the air conditioning unit in the ceiling was on at the time.
Diagram of the outbreak at a South Korean restaurant equipped with ceiling-type air conditioners: arrows represent the air flow. Curved air streamlines represent where air is reflected off a wall or barrier, and moves downward toward the floor.(Korean Academy of Medical Sciences)
Lee and his team re-created the conditions in the restaurant — researchers sat at tables as stand-ins — and measured the airflow. The high school student and a third diner who was infected had been sitting directly along the flow of air from an air conditioner; other diners who had their back to the airflow were not infected. Through genome sequencing, the team confirmed the three patients’ virus genomic types matched.
“Incredibly, despite sitting a far distance away, the airflow came down the wall and created a valley of wind. People who were along that line were infected,” Lee said. “We concluded this was a droplet transmission, and beyond” 6.6 feet.
The pattern of infection in the restaurant showed it was transmission through small droplets or larger aerosols either landing on the face or being breathed in, said Marr, the Virginia Tech professor who was not involved in the study. The measured air velocity in the restaurant, which did not have windows or a ventilation system, was about 3.3 feet per second, the equivalent of a blowing fan.
“Eating indoors at a restaurant is one of the riskiest things you can do in a pandemic,” she said. “Even if there is distancing, as this shows and other studies show, the distancing is not enough.”
The study was published at a time when South Korea, like many other countries, is on edge amid a new wave of coronavirus infections, with daily case rates hovering around 600 in recent days. Seoul, the capital, this week began requiring restaurants to close by 9 p.m., limiting coffee shops to takeout only and forcing clubs and karaoke bars to shut down.
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