A study published in mid-June in the journal Physics of Fluids found that flushing a toilet can generate a cloud of aerosol droplets that rises nearly three feet. As reported by Knvul Sheikh of the New York Times, 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.

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.

 “The aerosols generated by toilets are something that we’ve kind of known about for a while, but many people have taken for granted,” said Joshua L. Santarpia, a professor of pathology and microbiology at the University of Nebraska Medical Center who was not involved in the research. “This study adds a lot of the evidence that everyone needs in order to take better action.”]

Typically, the coronavirus is most at home in cells in the lungs and upper respiratory tract. But studies have found it can also dock to cell receptors in the small intestine. Patients have been reported to experience diarrhea, nausea and vomiting among other symptoms.

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 is 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 to 60 percent of the produced aerosols high above the seat.

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

It’s virtually impossible to keep bathrooms sanitized all the time, and sharing a toilet may be unavoidable for family members, even when one person is sick and isolating in a separate room at home, Dr. Wang said.

As cities around the world navigate the reopening of restaurants, offices and other businesses, more and more people will also need to use public or shared restrooms. But while diners can be moved outdoors and employees spaced out, people may find it harder to practice social distancing in small bathrooms.

Aerosolized particles may still linger in single-use toilets, and bathrooms are frequently poorly ventilated spaces, which can increase the risk of exposure to infection. Users also have to consider risks from high-touch surfaces, like doorknobs and faucets.

Experience with other coronaviruses shows how quickly the fecal-oral route can lead to spread of disease. In March 2003, more than 300 people living in the Amoy Gardens apartment complex in Hong Kong got infected with the original SARS coronavirus because infectious fecal aerosols spread through faulty plumbing and ventilation systems.