The coronavirus may have spread through the ventilation system of an apartment complex in South Korea, where several residents of different families were infected, according to a study.
The cluster was investigated after a series of new COVID-19 cases were identified in August on several floors of the Seoul residential complex, according to the article in the International Journal of Infectious Diseases.
On August 23, a woman who lives on the sixth floor tested positive, followed by her husband and daughter.
The next day, a child who lived in the unit below went to the hospital for an urological problem and also tested positive for the virus, the researchers wrote.
When another woman who lived directly below them on the fourth floor was diagnosed with COVID-19, health officials decided to test all 437 residents.
The mother of the infected child also tested positive, along with two more residents who lived in units directly above them on the 10th and 11th floors, the researchers said.
Two more cases were found in other units on the second and 11th floors of the tower.
These units are not directly above or below each other, but are on the same vertical line as each other and share the same ventilation system, the researchers said.
“All patients reported that they do not know each other and denied a history of interpersonal contact,” wrote the researchers.
The researchers said it is possible for the virus to spread across shared spaces, such as elevators.
But they noted that all infected residents reported wearing masks outside their apartments – and two even denied using the elevators.
They also pointed out that “among residents of more than 200 households who can use the same elevators, all patients were found on only two vertical lines in the building”
“Each line was connected by a single air duct in the bathroom for natural ventilation,” wrote the researchers.
“Our investigation found no other possible contact between the cases other than the airborne infection through a single air duct in the bathroom.”
The researchers, however, note that there were some limitations to the study, since they were unable to collect air samples.
But the findings suggest that more research is needed on the potential risk.
“More people may have to stay at home during the pandemic to avoid interpersonal contact,” concluded the researchers.
“However, some may be exposed to viral infection by inhalation due to inadequate ventilation systems.”