A new study investigating how nine people in three families became infected with COVID-19 found live pathogens produced by toilet flushing could have been responsible.
The research, published on Tuesday in the Annals of Internal Medicine, looked at the families living directly above each other in a high-rise apartment building in Guangzhou, China.
One of the families “had a history of travel to the coronavirus disease epicentre in Wuhan” but the other two families had no such travel history and developed symptoms later.
“The families lived in three vertically aligned flats connected by drainage pipes in the master bathrooms,” the study read.
“Both the observed infections and the locations of positive environmental samples are consistent with the vertical spread of virus-laden aerosols via these stacks and vents.”
The researchers concluded: “On the basis of circumstantial evidence, fecal aerosol transmission may have caused the community outbreak of COVID-19 in this high-rise building.”
The nine infections were confirmed during the height of the pandemic there, between January 26 and February 30, while residents in Guangzhou were social distancing.
Researchers collected data from each of the families, including where they had recently travelled, whether they had been in contact with infected individuals and what symptoms they experienced.
Family A, including four members, travelled to Wuhan in early January. Families B and C, who lived directly above Family A, included two middle-aged couples who stayed home during most of January and became infected in early February.
Researchers used a detailed design of the building, including how the drainage systems in each apartment worked.
A diagram shared with the research illustrates how, in theory, toilet fumes from infected individuals could escape through drains in the floors and in the bathtub of apartments above.
The researchers tested their theory by releasing ethane into the drainage system to represent virus-laden droplets, they said.
Importantly, they found that “throat swab specimens from 217 other people (in the apartment block) were all negative”.
“Our epidemiologic and environmental data indicate that the infection source for patients in flat 2502 (Family B) and possibly those in 2702 (Family C) was probably the master bathroom of flat 1502 (Family A), and virus-containing fecal aerosols were probably produced in the associated vertical stack during toilet flushing after use by the index patients,” they wrote.
It is not the first time such research has been conducted. The National Centre for Biotechnology Information wrote in research headlined “Put a lid on it” that “bio-aerosols containing live pathogens can be produced by toilet flushing”.
Nick Talley, editor-in-chief of the Medical Journal of Australia, is on the fence about whether COVID-19 can be transferred by the flushing of toilets.
He wrote on Twitter about the Annals of Internal Medicine research: “Interesting but speculative.”