Recently, researchers from Guangzhou CDC and Guangzhou Yuexiu District CDC published an online research bulletin “COVID- 19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020 “, one of the corresponding authors of the paper is Yang Zhicong, director of Guangzhou CDC

This study retrospectively analyzed an outbreak that occurred in a restaurant using air conditioning in Guangzhou in January this year, involving 3 families eating at the same time period, A total of 10 people were diagnosed as COVID-19. Research suggests that in this chain of transmission, droplet transmission is caused by air conditioning and ventilation, and the key factor for infection is the direction of airflow.

At present, although the epidemic situation in many places in the country has basically calmed down, many activities involving intensive people such as resuming work, starting school and traveling are still proceeding with caution. Through this research, Yang Zhicong and others reminded that in order to prevent the spread of COVID-19 in restaurants, it is recommended to strengthen temperature monitoring, increase the distance between tables and improve ventilation.


Dined in the same restaurant, the distance between the tables is about 1 meter

The details of the paper show that from January 26 to February 10, 2020 On the 10th, 10 people from 3 families (AC families) in Guangzhou, China were infected with the new crown virus. They used to dine in the same air-conditioned restaurant. One of the families just came from Wuhan, Hubei.

Researchers conducted detailed investigations on these 10 cases. On January 23, Family A departed from Wuhan and arrived in Guangzhou. On January 24, the indicated case (Patient A1) and three other family members (A2-A4) had lunch at Restaurant X. The other two families, B and C, sit at the table adjacent to the same restaurant.

Later in the day, patient A1 developed fever and cough and was admitted to hospital for treatment. As of February 5, a total of 9 people (4 in A, 3 in B, and 2 in C) were infected with COVID-19.

The only known source of contact for infected persons in families B and C is patient A1 in the restaurant. The researchers determined that the virus had spread to at least one person in the restaurantFamily member B and at least one member of family C. Further infections in family B and family C are caused by transmission within the family.

The paper mentioned that Restaurant X is a five-story building with air conditioning and no windows. The third floor of the restaurant has an area of ​​145 square meters; each floor has its own air conditioner (picture). The distance between each table is about 1 meter. Family A and B spend 53 minutes together in the restaurant, family A and C spend 73 minutes. The air outlet and return outlet of the central air conditioner are located above the C table.

On January 24, a total of 91 people (83 customers, 8 staff) dine in this restaurant. Among them, a total of 83 people had lunch at 15 tables on the third floor. Of the 83 clients, 10 were finally diagnosed as COVID-19 patients.

Another 73 people were identified as close contacts and were quarantined for 14 days. During this period, these contacts did not show any symptoms. The reverse transcriptase polymerase chain reaction test showed that the contact’s throat swab samples and 6 samples from the air conditioner (3 from the air outlet and 3 from the air inlet) were negative.


The air conditioning or “boosted” the droplet relay

After examining the potential transmission routes, the researchers concluded that this outbreak was the most The possible cause is the spread of droplets. Although the indicated case (Patient A1) was asymptomatic during lunch, the current study is generally pre-symptomatic.

Researchers believe that, considering the incubation period of the B family, the most likely situation is that all three B family members are directly infected by patient A1. However, the possibility of patients B2 and B3 being infected by patient B1 cannot be ruled out. B1 is the first member of the B family to develop the disease.

For family C, it is possible that patients C1 and C2 are both infected by patient A1; another situation is that from January 27, patient C1 is in care Patient C2 was infected.

They emphasized that the spread of this epidemic cannot be explained by droplet transmission alone. Larger respiratory tract droplets (> 5 microns) only stay in the air for a short time, and the propagation distance is also short, generally less than 1 meter. The distance between patient A1 and other tables, especially table C, is greater than 1 meter.

However, the strong airflow from the air conditioner may spread droplets from the C table to the A table, then to the B table, and then back to the C table (Air outlet → C → A → B → air inlet).

It is also worth noting that the small droplets (<5 microns) that enclose the virus can stay in the air and can spread over a long distance of more than 1 meter. Previous reports have suggested that there is potential for aerosol transmission in the spread of SARS and MERS.

However, the staff of Restaurant X and other diners were not infected. Air conditioning smears were also nucleotide negative. The researchers therefore believe that this finding is not consistent with aerosol transmission.

Researchers analyze that aerosols tend to follow the airflow, and lower concentrations of aerosols may not be sufficient to cause infections in other places of the restaurant at longer distance .

The so-called aerosol transmission refers to the nucleus of protein and pathogens left by the water droplets lost in the air suspension process, forming the droplet nucleus, which can pass through the air The form of sol floats far away, causing long-distance propagation. There is currently no evidence that the new coronavirus is transmitted by aerosol.

In the “New Coronavirus Pneumonia Diagnosis and Treatment Program (Trial Sixth Edition)” issued by the National Health and Health Commission, the original “aerosol and digestive tract, etc.” The official way of transmission is yet to be clarified. “The official statement was changed to” the possibility of transmission through aerosols in a relatively closed environment when exposed to high concentrations of aerosols for a long time ”

In general, the researchers concluded in this study that in this transmission chain, the transmission of droplets is caused by air conditioning and ventilation, and infection The key factor is the direction of airflow. It is worth noting that patient B3 is asymptomatic, and 1% of patients in this outbreak are asymptomatic, which also suggests that this potential pathway exists in the outbreak.

In order to prevent the spread of COVID-19 in the restaurant, the researchers recommend strengthening temperature monitoring, increasing the distance between the tables, and improving ventilation.

This study also has its limitations. The researchers mentioned that they did not conduct experimental studies to simulate the airborne transmission path, nor did they perform serological studies on asymptomatic family members and other diner-negative swab samples to assess the risk of infection.

Link to the paper: https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article