This picture shows how 9 people in a restaurant got the coronavirus thanks to the placement of an air conditioning unit

• A diagram shows how an AC unit at a restaurant in Guangzhou helped infect nine people with the coronavirus.
• 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."
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A diagram shows how an air-conditioning unit at a restaurant in China helped infect nine diners with the coronavirus.

The diagram was included in a letter from several scientists in Guangzhou published this week in the Emerging Infectious Diseases Journal, based at the US Centres for Disease Control and Prevention (CDC.)

In it, the authors explained how the AC unit blew respiratory droplets around the windowless air-conditioned restaurant on January 24. The restaurant was not named.

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.

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."

Research so far has suggested that the coronavirus is transmitted by droplets, or heavy particles. In normal circumstances they tend not to float farther than one meter, as Business Insiders' Shira Feder previously reported.

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.

There have been calls for restaurants to reduce their capacities when they reopen after lockdowns end.