Close the Lid! Flushing Toilets Spreads Coronavirus

Henrietta Strickland
June 16, 2020

Despite businesses reopening and states relaxing their stay at home restrictions, the threat of COVID-19 still looms large.

For the study, Wang and colleagues created computer simulations of how water and air flows in flushing toilets create droplet clouds that can contain viruses and bacteria.

"Flushing will lift the virus up from the toilet bowl", Ji-Xiang Wang, who researches fluids at Yangzhou University in Yangzhou, China, said.

According to the newspaper, a study of air samples conducted in Wuhan, China, where the pandemic originated, found that coronavirus aerosols were higher in toilet areas used by patients. The simulations included two types of toilets - one with a single inlet for flushing water, and another with two inlets for water to create a rotating flow. These vortices continue upward into the air above the bowl, carrying droplets to a height of almost 3 feet, where they might be inhaled or settle onto surfaces.

Simulation results of single-inlet flushing
Close the Lid! Flushing Toilets Spreads Coronavirus

The investigators also used a discrete phase model to simulate movement of the numerous tiny droplets likely to be ejected from the toilet bowl into the air. These droplets are so small they float in the air for over a minute. Toilets with two ports create an even greater velocity of aerosol particles; simulations showed that with two-port toilets, almost 60% of aerosol particles rise above the seat (for single-port toilets, that figure was around 40%). "It can be imagined", the researchers write, "that the velocity will be even higher when a toilet is used frequently", such as a public toilet used by a lot of people. Some of the symptoms of the virus include vomiting and diarrhea, but the Center for Disease Control and Prevention (CDC) has said that it is unclear whether virus found in feces can cause the disease.

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.

"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. "While this study is unable to demonstrate that these measures will reduce transmission of the SARS-CoV-2 virus, many other viruses are transmitted though the fecal-oral route, so these are good hygiene practices to have anyway". But most importantly, he adds, "Toilet manufacturers should design a new toilet in which the lid is automatically put down before flushing".

Other reports by Click Lancashire

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