Why care for indoor air?

Outbreak at a restaurant

The Restaurant, China

A New Year’s celebration in the Chinese city of Guangzhou provides the best example of how to reduce indoor risks. Two different studies concluded that poor ventilation can be a decisive risk factor if contact is maintained during prolonged periods.

Let’s take a closer look at the conditions


The restaurant was full the day of the celebrations. The outbreak happened in a room with no natural ventilation where around 90 people were eating with 8 waiters serving.


On table A, a person who had arrived the day before from Wuhan was eating with their family. That night, that person showed symptoms and went to hospital and tested positive for Covid-19..


After the meal, another 9 customers were diagnosed with Covid-19. All those infected from tables B and C were more than a meter away from Patient 0, some as far as 4.5 meters. No one else in the restaurant became infected.


Length of time is critical. The meals of families B and C overlapped with that of Patient 0 for an extended period, while those at table D only overlapped with Patient 0 for 18 minutes.


Researchers believe that the air conditioning played a crucial role. It meant the air was recirculating continuously between the three tables, concentrating the tiny, virally charged micro-droplets that Patient 0 was expelling into the atmosphere among these customers.

Conclusions from the studies

Cameras on the premises show that those infected had no contact in the washrooms or elsewhere that could have led to the transmission of the virus. Although close contact can play an important role in the transmission of SARS-CoV-2, transmission of the virus in small airborne droplets “in crowded, poorly ventilated rooms” is also possible, according to the scientists. Outdoor air vents in the restaurant were closed. “Our study suggests that it is vital to prevent overcrowding and provide good ventilation in buildings and public transportation to prevent the spread of SARS-CoV-2,” they add. The recommendations from the health authorities invariably insist on avoiding recirculating air, as well as holding activities outside whenever possible.

How do we minimize the spread of infection

  • Avoid recirculation of the air.
  • Make sure you have good ventilation. Open windows if possible.
  • Always use air filters and clean them regularly 
  • Minimize the length of restaurant visits  
  • Avoid loud background music so that visitors do not have to raise their voices or sit close to hear each other.
  • Reduce the size of parties indoors 
  • Increase the distance between people
  • Arrange events outdoors if possible

Links to similar studies and analyzes


  1. El País, https://english.elpais.com/society/2020-10-28/a-room-a-bar-and-a-class-how-the-coronavirus-is-spread-through-the-air.html, https://english.elpais.com/spanish_news/2020-06-17/an-analysis-of-three-covid-19-outbreaks-how-they-happened-and-how-they-can-be-avoided.html, Authors: Javier Salas (javier@esmateria.com), Mariano Zafra
  2. US Centers for Disease Control and Prevention, Centers for Disease Control and Prevention in Guangzhou and Hangzhou, The Johns Hopkins Center for Health Security, the Spanish National Research Council’s Institute of Environmental Assessment and Water Studies (IDAEA-CSIC), European Centre for Disease Prevention and Control, International Laboratory for Air Quality & Health (WHO, Queensland), and the government of South Korea.

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