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Possible aerosol transmission of COVID-19 associated with an outbreak in an apartment in Seoul, South Korea, 2020

Our take —

This study described likely aerosol transmission of SARS-CoV-2 among residents of an apartment building in Seoul, South Korea. Among 442 individuals tested from the building, a total of 10 cases were identified. All cases resided along two vertical lines in the building. While investigators hypothesized possible transmission through use of common areas such as elevators, they inferred that the most plausible transmission route was forced exhaust of aerosols from bathrooms of infected persons to the air duct entering bathrooms without a ventilator or bathrooms with nonfunctional ventilators. Transmission through air ducts warrants further research to better inform indoor transmission risks.

Study design

Case series; cross sectional

Study population and setting

This study examined possible aerosol transmission of SARS-CoV-2 among residents of an apartment building in Seoul, South Korea. On August 23, 2020, residents of a 6th floor unit tested positive for COVID-19. The next day, a toddler living on the 5th floor visiting a hospital for an underlying condition was diagnosed with COVID-19. On August 25, a 4th floor resident was diagnosed with COVID-19 and reported having a fever since August 22. All five persons with COVID-19 were in the same vertical line of the apartment building. Further investigation of 437 residents from 267 households identified five more cases, including the toddler’s mother, two individuals on 10th and 11th floors on the same vertical line as the other cases, and two individuals on the 2nd and 11th floors of the next vertical line.

Summary of Main Findings

Apartment residents with COVID-19 reported that they were not acquainted with one another and had no interpersonal contact. While investigators noted possible transmission through droplet infection in common spaces such as elevators, or use of elevator buttons, all patients noted that they had worn masks whenever outside their units, and two patients said they did not use the elevators. The other possibility hypothesized by the authors was that the index case released the virus during a shower by coughing, singing, or breathing; the virus then combined with water vapor and became aerosols in the humid environment. Bathroom mechanical ventilators likely then force exhausted the aerosols into the air duct, allowing spread to upper floors and lower floors (i.e., reverse stack effect in the summer) entering bathrooms without a ventilator or those with a nonfunctional ventilator.

Study Strengths

Cases of COVID-19 were confirmed through PCR tests, and hundreds of residents were tested within the apartment building to identify as many cases as possible.


Investigators only outlined possible transmission scenarios, without genomic sequencing or air sampling to provide detailed evidence of aerosol transmission, or to rule out other potential mechanisms. In addition, there was no information about how the likely index case may have become infected with SARS-CoV-2.

Value added

This study calls attention to the potential role of inhalation of aerosols due to inadequate ventilation systems as a possible route by which SARS-CoV-2 infection occurs within shared housing.

This review was posted on: 13 June 2021