The paper we’ll be demystifying can be found here, if you’d like to follow along!
This article was reviewed by Dr. Zachary Benet, one of our subject matter experts.
A COVID-19 outbreak infected 10 people from 3 different families, who all ate lunch at the same restaurant. The outbreak most likely occurred from droplet transmission and the restaurant’s air conditioner most likely spread the virus droplets.
Between January 26th to February 10th, 2020, a COVID-19 outbreak infected 10 people from three different families (families A-C). The only connection between the three families was that they had all eaten from the same restaurant. This was an air-conditioned restaurant located in Guangzhou, China. However, one member from a specific family had recently travelled to Wuhan, China, prior to eating at the restaurant. The researchers in the present study performed an investigation to determine the cause of the COVID-19 outbreak.
Restaurant Lay Out
The restaurant was in a 5-floor building that had no windows. Each floor had a separate air conditioner. The restaurant was located on the third floor of the building and the space was a total of 145 m2. The distance between each table in the restaurant was around 1m.
Seating Arrangements of Families A, B and C
Families A, B, and C were seated at neighbouring tables. The return air inlet and the air outlet from the restaurant’s air conditioner were located above the table where Family C sat. Families A and C were at the restaurant at the same time for about 73 minutes, whereas families A and B were at the restaurant at the same time for about 53 minutes.
Onset of Illness
On January 23rd, 2020, patient A1 (member of family A) travelled from Wuhan to Guangzhou. The following day on January 24th, patient A1, ate with three other family A members (patient A2, A3 and A4), at the air-conditioned restaurant located in Guangzhou. Families B and C were also at the restaurant on January 24th and were sitting at neighbouring tables. Later that day, patient A1 began experiencing COVID-like symptoms that consisted of a fever and cough. By February 10th, 2020, 10 people from family A, family B and family C were diagnosed with COVID-19.
How Transmission Occurred
The only known exposure to COVID-19 for the COVID-positive members of families B and C was patient A1. Patient A1 had most recently travelled to Wuhan, China, where they most likely were infected. COVID-19 was most likely transmitted to ≥1 member from family B and C. Further transmission most likely occurred between family members. Therefore, the researchers concluded that droplet transmission was most likely the cause of the outbreak. Droplet transmission is when a person has close physical contact (<1 m) with someone with respiratory symptoms (e.x. cough) and thus, their mouth, nose, and eyes are exposed to respiratory droplets.
Patient A1 had no COVID-like symptoms while at the restaurant. However, studies have found that transmission of COVID-19 can still occur, even if the person has no symptoms. The researchers believe that the 3 infected members from family B were most likely infected through transmission from patient A1. There is also the possibility that patient B1 (member of family B) was directly infected by patient A1 as patient B1 was the first family member to become ill with COVID-19. Following this, patient B1 may have infected patient B2 and patient B3. Patients C1 and C2 (members of family C) were possibly infected through transmission from patient A1. There is another possibility that patient C1 may have gotten infected while taking care of patient C2.
Droplet transmission is not the complete explanation of how this outbreak occurred. Larger respiratory droplets (which are around >5 μm) can only travel distances of <1 m. The distances between patient A1 and families B and C were >1 m. Aerosolized virus droplets can stay in the air and travel distances of >1 m. As the air conditioner in the restaurant had strong airflow, there is the possibility that the strong airflow spread the respiratory droplets. The respiratory droplets were most likely moved from table C (where family C was sitting) to table A (where family A was sitting), then moved to table B (where family B was sitting) and then returned to table C.
As previously stated, 10 people were infected with COVID-19. These 10 people were from families A, B, and C. However, a total of 91 people (8 staff members and 83 diners) were at the restaurant on January 24th. Specifically, the 83 diners (including families A-C) had lunch on January 24th on the third floor of the restaurant. The 73 diners that were in close contact with the 10 people infected with COVID-19 were asked to quarantine for 14 days, following the outbreak. During the 14 days of quarantine, none of the 73 diners developed COVID-like symptoms and throat samples tested negative for SARS-CoV-2 through RT-PCR tests. However, the concentration of virus aerosols may have been lower at great distances and insufficient to infect the 73 diners and the staff who were in other areas of the restaurant. Moreover, smear samples were taken from the air conditioner also tested negative for SARS-CoV-2 through RT-PCR tests.
The researchers of the study did not perform an experimental study to stimulate the potential route of the airborne transmission. This may have limited their conclusions. The researchers also may have limited their conclusions by not conducting serologic studies of swabs from non-infected people to determine the risk of COVID-19 infection.
Conclusion and Implications
10 people from three different families were infected with COVID-19, after eating at the same restaurant on the same day. The outbreak most likely occurred from droplet transmission and the air conditioner may have moved the virus droplets. An important factor that contributed to the outbreak was the direction of the airflow from the air conditioner.
To prevent COVID-19 outbreaks in restaurants, the researchers of the study recommend improving ventilation in restaurants, ensuring social distancing by increasing the space between tables and surveying temperatures of people before they enter restaurants.