Back in February, in Guangzhou, China, five people who lived in the same apartment tested positive for COVID-19. The apartment directly above this family was vacant and had been vacant for a very long time. Yet, scientists found traces of COVID-19 in the apartment’s bathroom – on the sink, on the sink’s faucet, and on the shower handle. How could COVID-19 exist in a bathroom that hadn’t been used since before the virus even existed?

Lidia Morawska is the director of the International Laboratory for Air Quality and Health at Australia’s Queensland University of Technology. She wasn’t part of the research team in the study in China, but she able to describe just in fact how the virus spread to the vacant apartment. She said that sometimes apartment buildings with more than one story are linked by a shared wastewater system. Solids and liquids move down through the pipes, but sometimes sewer gases move upwards when there isn’t water to push them down. 

It has already been proven that COVID-19 is spread through respiratory droplets, such as saliva when we cough or sneeze, but scientists also believe that it can be spread through toilets. 

Scientists in China believe that when someone with COVID-19 flushes the toilet, the aerosols can spread as far away as 3 feet, especially in poorly ventilated areas, and in this case of the vacant apartment, it appears that the aerosols traveled up the pipes to the vacant apartment.

Malik Peiris is the chair of virology at the University of Hong Kong’s School of Public Health, and he points out something very important. While scientists found traces of COVID-19 in the vacant apartment in China, that does not mean that there was enough of the virus on the surfaces to make it an infectious virus. Yet, he cautions, “one has to keep the possibility in mind.”

In another case, this time on an airplane, an asymptomatic yet COVID-19 positive passenger used the bathroom. Later, another passenger who had been wearing an N-95 mask during the entire flight used the same airplane bathroom but did not wear the mask while in the bathroom. This second passenger later tested positive for COVID-19 as well, and researchers believe that the contamination may have been from the bathroom.