Flushing toilet may cause virus to spread

Here’s one more behavior to be hyper-aware of to prevent coronavirus transmission: what you do after you use the toilet.

Scientists have found that flushing a toilet can generate a cloud of aerosol droplets that rises nearly 3 feet. Those droplets may linger in the air long enough to be inhaled by a shared toilet’s next user, or land on surfaces in the bathroom.

This toilet plume isn’t just gross. In simulations, it can carry infectious coronavirus particles that are already present in the surrounding air or recently shed in a person’s stool.

The research, published Tuesday in the journal Physics of Fluids, adds to growing evidence that the coronavirus can be passed not only through respiratory droplets but also through virus-laden feces, too.

And while it remains unknown whether public or shared toilets are a common point of transmission of the virus, the research highlights the need during a pandemic to rethink some of the common spaces people share.

Typically, the coronavirus is most at home in cells in the lungs and upper respiratory tract. But studies have found it also can dock to cell receptors in the small intestine.

And researchers have found viable virus particles in patients’ feces, as well as traces of viral RNA on toilet bowls and sinks in their hospital isolation rooms, although experiments in the lab have suggested that material may be less likely to be infectious compared with virus that’s coughed out.

A computer simulation of the toilet flushing mechanism showed that when water pours into the toilet and generates a vortex, it displaces air in the bowl. These vortices move upward and the centrifugal force pushes out about 6,000 tiny droplets and even tinier aerosol particles.

Depending on the number of inlets in the toilet, flushing can force anywhere from 40 percent to 60 percent of the produced aerosols high above the seat.

“It’s very alarming,” said JiXiang Wang, who studies fluid dynamics at Yangzhou University and was a co-author of the study.

Thankfully, people can easily prevent the spread of infections from the toilet plume.

“Close the lid first and then trigger the flushing process,” Wang said.