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Crowded or Poorly Ventilated Spaces May Increase Virus Spread, Evidence Suggests

poorly ventilated spaces

Crowded or Poorly Ventilated Spaces May Increase Virus Spread, Evidence Suggests

Indoor air quality, ventilation, and occupancy have become growing concerns in the battle to slow the spread of COVID-19. So much so, that Sasha Wedekind, research analyst on building efficiency and decarbonization, insists COVID-19 has catapulted indoor air quality “to the top of the list.” This assertion is supported by various evidence, but two case studies published by the Centers for Disease Control and Prevention provide real data suggesting that airflow and ventilation can play a major role in COVID-19 transmission.

COVID-19 Outbreak Associated with Air Conditioning in Restaurant

This case study followed a COVID-19 outbreak in an air-conditioned restaurant, located in Guangzhou, China. The outbreak affected 10 individuals among three separate families, and a detailed investigation was conducted linking the case together.

Key Findings

  • The index-case patient (referred to as patient A1) ate lunch with three other family members (referred to as A2–A4) at the restaurant, next to two other families (referred to as B and C). Later that day, patient A1 experienced onset of fever and cough and went to the hospital and by February 5, a total of nine others – including members from families A, B and C were infected.
  • The only known source of exposure for the affected persons in families B and C was patient A1 at the restaurant.
  • The restaurant is an air-conditioned, 5-floor building without windows. The third floor has its one air-conditioning unit, and the distance between each table is about 1 m. Families A and B were each seated for an overlapping period of 53 minutes and families A and C for an overlapping period of 73 minutes. The air outlet and return inlet for the air-conditioner was above family C.
  • The airflow direction was consistent with the droplet transmission of COVID-19.


Given the diagram above, it is apparent that the airflow in the restaurant has played a role in the transmission of COVID-19. Air flow was consistent with droplet transmission, providing evidence of exacerbated transmission in high-occupancy areas and spaces with limited ventilation.

Coronavirus Disease Outbreak in Call Center

This case study followed a COVID-19 outbreak within a call center located in South Korea. The outbreak affected 97 persons, predominantly within the same call center on the eleventh floor.

Key Findings

  • Outbreaks of COVID-19 related to mass gathering, religious activities, workplaces, and hospitals have accounted for the largest portion cases in South Korea outbreaks.
  • On March 8, the Seoul Metropolitan Government was notified of a confirmed case of COVID-19 in a person who worked in “building X”; the case reportedly was associated with a possible cluster of cases.
  • “Building X” is a 19-story floor in one of the busiest urban areas of Seoul. Commercial offices are located on the 1st through 11th floors, and residential apartments are located on the 13th through 19th floors.
  • Of 1,145 patients under investigation, 1,143 were tested for COVID-19 and 97 were identified as confirmed case patients.
  • 97 confirmed COVID-19 case-patients in building X, indicating an attack rate of 8.5%. Most (96.9%) of the confirmed case-patients were working on the 11th-floor call center, which had a total of 216 employees, resulting in an attack rate of 43.5%.


This case study outlines the importance of being aware of occupancy levels in office settings, as well as identifying potential risks early on. The transmission of COVID-19 was exacerbated by the lack of distance between individuals and inability to create an efficient ventilation management process.

Best Practices for Building Ventilation and Air-Conditioning

  • Increase fresh air intake as much as possible
  • Increase filtration efficiency
  • Increase space between occupants
  • Gather data on your indoor air quality
  • Control key indoor air quality parameters
Not sure where to start?

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