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