Patient A1 was infected with COVID-19, but asymptomatic when they dined with their family (A2-5) on January 24.
The AC picked up air droplets from the breath of patient A1 and blew them around the room. Water droplets usually don't travel more than a meter without assistance.
Nine other people (four members of A, three of B, and two of C) later tested positive for COVID-19 and were traced to to A1.
"The key factor for infection was the direction of the airflow," a group of scientists from Guangzhou wrote in a letter published in the Emerging Infectious Diseases Journal. "Droplet transmission was prompted by air-conditioned ventilation."
The diagram shows an infected person, referred to as A1. They had arrived from Wuhan with A2 and A4 on January 23. Despite having the virus, they were not displaying symptoms.
A1 only reported symptoms later the day of the restaurant visit, and went to a hospital.
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By February 5, nine other diners (four members of family A, three members of family B, and two members of family C) had tested positive for COVID-19.
"Droplet transmission was prompted by air-conditioned ventilation. The key factor for infection was the direction of the airflow," the authors wrote.
"Strong airflow from the air conditioner could have propagated droplets from table C to table A, then to table B, and then back to table C."
The AC circulated air in the room constantly. Members of the A and C families shared the same room for 73 minutes. A and B shared the room for 53 minutes.
The tables were located one meter apart, the authors wrote.
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