New study finds coronavirus particles could be carried by ‘toilet plume’ when flushing

Close the lid before flushing or risk expelling thousands of tiny particles containing the coronavirus more than three feet into the air, a new study published Tuesday warns.

Physics researchers in China used computational fluid dynamics to show that a standard toilet flush can expel 40 to 60 percent of the aerosol particles in the bowl, which can then hang in the air for several minutes.

Previous studies have indicated that the novel coronavirus can survive in the air, especially in areas with poor ventilation, such as bathrooms. The aerosolized particles can linger for several hours.

While the novel coronavirus is primarily transmitted through respiratory droplets, viable virus particles have been detected in some patients’ feces, according to the Centers for Disease Control and Prevention. There are no confirmed cases of transmission to a person via feces.

Published in the journal Physics of Fluids, Tuesday’s study found that a flush creates “airflow vortices” in the toilet bowl that can eject thousands of particles far above the seat. Computer simulations showed that particles continued to climb more than a minute after a flush.

The next user could then ingest the particles or touch them on another bathroom surface.

Given that other coronaviruses such as severe acute respiratory syndrome are known to have spread through fecal-oral transmission, toilets could potentially be a source of “large-scale” novel coronavirus spread, the study’s authors wrote.

“Toilets are a daily necessity but also become dangerous if used improperly, especially against the current scenario of a global pandemic,” the researchers wrote.

But just a few simple steps can mitigate the hazard.

Users should clean a toilet seat before using it in case aerosol particles from the previous flush settled there, the authors wrote. After flushing — with the toilet lid down — they should wash their hands in case particles landed on other bathroom surfaces.

University of Arizona microbiologist Charles Gerba told The Washington Post on Tuesday that the hazards posed by so-called toilet plumes, which have been studied since the 1950s, depend on the transmissibility of respiratory viruses through feces.

“The big unknown is how much virus is infectious in the toilet when you flush it … and how much virus does it take to cause an infection,” Gerba said.

Viral RNA in feces can be used to track outbreaks through sewage, a technique already being deployed against the novel coronavirus in several cities. In terms of transmission, however, early research has indicated that virus particles become inactivated by the time a patient uses the toilet.