Coronavirus (COVID-19): In a recent paper, Chinese researchers have talked about an incident in a restaurant in Guangzhou, China, in which one coronavirus-positive diner passed on the infection to nine more people dining there, but not to others. The research will be published in the journal Emerging Infectious Diseases in July.
Apart from droplet transmission, researchers suspect that larger respiratory droplets suspended in the air could have infected the diners aided by the airflow of the air conditioner.
On January 23, family A travelled from Wuhan to Guangzhou. On January 24, the index patient, A1 (the infected individual), dined with three other family members at restaurant X. At this restaurant, two other families B and C sat at neighbouring tables.
Later that day, index patient A1 started developing symptoms, including fever and cough, and reported to the hospital. Nine more people (four members of family A, three members of family B and two members of family C) had been infected with SARS-CoV-2.
The only known source for members of family B and C to get infected was patient A1. So then, how could they be infected?
The dynamics within the restaurant
Restaurant X is an air-conditioned establishment with five floors and no windows. The distance between each table is roughly 1 metre. On the day the three families dined at the restaurant, the overlapping time between A and B was over 53 minutes and that between A and C was roughly 73 minutes.
Researchers note that the air outlet and inlet for the central air conditioner was located above family C. On January 24, a total of 91 persons were at the restaurant, including staff members. Out of these, 83 people had lunch at 15 tables located on the third floor. Among these 83, 10 became ill with COVID-19 and the remaining 73 were treated as close contacts, quarantined for 14 days.
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Potential routes of transmission
As per researchers, “the most likely cause of this outbreak” could be droplet transmission. While patient A1 was asymptomatic during lunch, researchers think all three members of family B were directly infected by A1.
“However, we cannot not exclude the possibility that patients B2 and B3 were infected by patient B1, the first family B member to become ill,” they note.
For family C, one scenario is that two family members are infected by A1, another is that one got infected while taking care of the other infected patient.
Concluding that in this restaurant, droplet transmission was prompted by air-conditioned ventilation, researchers think that virus-laden aerosolised droplets could have been moved around from table C, to A, B and then back to table C.
Aerosolised droplets that are large or greater than 5μm remain in the air for only a short period of time and can travel distances less than 1 metre. However smaller respiratory droplets of size less than 5μm can remain in the air for a longer period of time and can travel distances greater than 1 metre.
But why did only members of family B and C get infected? Aerosols tend to follow the airflow and the lower concentration of aerosols at greater distances from table A might have been insufficient to infect other people dining at the restaurant.
In an illustration of the seating arrangement shared by the researchers, table A is placed in the centre of B and C, while the air conditioner was placed next to table C. All three tables were placed in an area 6 metre in length.
Therefore, the direction of airflow and the air-conditioned ventilation could have played a significant role in the transmission dynamics of this restaurant. “To prevent spread of COVID-19 in restaurants, we recommend strengthening temperature-monitoring surveillance, increasing the distance between tables, and improving ventilation,”says the study.
These observations may be significant considering that droplets can be transmitted not only while coughing or sneezing, but also while talking and breathing, as a few recent research studies have shown.
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