Could Flushing a Public Toilet Really Spread COVID-19?

According to a new study just released by the American Institute of Physics, we’re all going to have to add bathrooms to our collective list of COVID-19 concerns.

Using computer simulations, the research team confirmed that flushing a toilet can indeed send a “cloud” of infectious coronavirus-containing aerosol droplets into the air. According to the study’s calculations, these droplets are large, widespread, and linger in the surrounding area for quite some time. All in all, this suggests it’s very possible for someone else to unknowingly breathe in the droplets and become infected themselves.

It’s been discussed and declared endlessly that the coronavirus is super contagious and capable of spreading quickly via aerosol droplets released when people breathe, cough, etc. Well, recent research has indicated that the coronavirus is also very capable of staying active within our digestive tracts and showing up in infected individuals’ feces. 

So, that’s why the team behind this study decided to investigate the plausibility of COVID-19 spreading through toilet flushing. Unfortunately, they found it is a very real possibility.

Whenever a toilet flushes, all of that swirling water sends tons of tiny water droplets into the air. It’s not something anyone notices very often because it’s happening on a microscopic scale. Nonetheless, there’s been various studies performed over the years that have indicated it’s at least possible for various viruses and strains of bacteria to spread via toilet flushing. For most of those pathogens the chances of actual transmission are slim, but the coronavirus is far more contagious than most viruses.

The computer simulations put together by the research team predicted the flow of water and air, as well as the resulting “droplet clouds,” from two distinct types of toilets. The first type was a toilet with a single inlet for flushing water, and the second type was a toilet with two inlets intended to create a rotating flow.

Then, another model was used to calculate the movement of all the aerosol droplets released into the air and surrounding environment by the flushing mechanisms.

The resulting findings leave little room for interpretation, the study’s authors say. Regarding a single inlet toilet, as the toilet is flushed and water pours into the bowl from one side a series of vortices (plural for vortex) are created. These vortices propel droplets upward into the air just above the bowl, and in some cases the viral particles reach as high as three feet above the toilet bowl. Once the viral droplets reach these heights they can linger in the air for over a minute before either being inhaled by someone or falling and infecting a nearby surface.

The results were even more striking for double inlet toilets. These models create even stronger vortices with more velocity, propelling viral droplets to even greater heights. In simulations of toilets with two inlets, close to 60% of all ejected droplets reached heights far above the toilet seat.

“One can foresee that the velocity will be even higher when a toilet is used frequently, such as in the case of a family toilet during a busy time or a public toilet serving a densely populated area,” says co-author Ji-Xiang Wang, of Yangzhou University, in a press release.

Of course, none of this is a problem at all as long as one closes the toilet lid before flushing. However, many public toilets in the United States don’t feature a lid, representing a potentially serious avenue of infection in public places all over the country. 

The full study can be found here, published in Physics of Fluids.

June 27, 2020