Flushing Toilet with Lid up Could Spread COVID-19 Through Cloud of Virus Particles, Study Suggests

Flushing the toilet without closing the lid risks spreading germs like the coronavirus that causes COVID-19, according to a study.

The authors of the paper, published in the journal Physics of Fluids, estimate that when the lid is left up during flushing, between 40 to 60 percent of aerosol particles in the bowl reach above the seat—potentially leading to "large-scale virus spread."

To carry out their study, the scientists looked at existing literature on the conditions of commons toilets and the air cloud caused by their flush mechanism to create a computer simulation.

Flushing a toilet was found to create "strong turbulence" and a velocity "which is certainly capable of lifting aerosol particles out of the toilet bowl," the team wrote.

To prevent the spread of germs like the coronavirus, which can be passed on through feces, the team advised putting the toilet lid down before flushing, cleaning the toilet before using it "since floating virus particles could have settled on its surface," and washing hands carefully after flushing as germs may be on the flush button and bathroom door handle.

Co-author Ji-Xiang Wang of China's Yangzhou University told Newsweek he was inspired to carry out the study while he was social distancing during the COVID-19 outbreak in China.

"I had nothing to do at home. I began to think of how a fluid researcher [could] contribute to the global fight against the virus." Flushing his toilet prompted him to hypothesize the process "may cause a massive spread of the virus."

Ji-Xiang said the paper was limited because the team looked at vertical airflow. Future studies should look at the horizontal airflow, he said.

Jeremy Rossman, an honorary senior lecturer in virology at the University of Kent in the U.K. who did not work on the study, told Newsweek the paper "provides additional modeling detail for how toilet flushing could generate aerosols, though the impact of these aerosols on virus transmission is not investigated."

Rossman said: "This route of transmission has not been proven [for COVID-19] and it is unlikely that this route is a major mechanism of virus spread throughout the community."

During the 2002-2003 SARS epidemic, the virus that caused that disease was found to spread through the sewage pipes of a Hong Kong apartment building through sewage pipes, and possibly through fecal aerosols generated during toilet flushing, said Rossman.

"It is known that flushing the toilet can generate airborne droplets that may contribute to the transmission of different pathogens and that closing the lid of the toilet seat is an effective way to minimize aerosol generation," he said. "We also know that COVID-19 can infect the gastrointestinal tract and the virus has been found in the feces of infected patients.

"Thus, it is possible that COVID-19 could be shed in the feces, aerosolized during toilet flushing and then infect the next person to enter the bathroom."