Close That Toilet Lid or the Air Might Be Flush with Coronavirus

Flushing the toilet might send the virus airborne.

Keep your distance!
Keep your distance!.

 John Keeble/Getty Images

The New York Times headline reads, "Flushing the Toilet May Fling Coronavirus Aerosols All Over." The Washington Post screams, "Put a lid on it, folks: Flushing may release coronavirus-containing ‘toilet plumes’." Treehugger says: This is news?

The stories are all based on a new study by researchers in China, titled Can a toilet promote virus transmission? From a fluid dynamics perspective and published in the scientific journal, the Physics of Fluids. The study authors (all engineers associated with technical universities) wonder if the SARS-CoV-2 coronavirus is spread through toilet usage.

It is clear from daily experience that flushing a toilet generates strong turbulence within the bowl. Will this flushing-induced turbulent flow expel aerosol particles containing viruses out of the bowl? This paper adopts computational fluid dynamics to explore and visualize the characteristics of fluid flow during toilet flushing and the influence of flushing on the spread of virus aerosol particles. 

It should be noted that the researchers didn't actually flush real toilets and measure this, but used a "volume of fluid (VOF)" model.

The simulation results are alarming in that massive upward transport of virus particles is observed, with 40%–60% of particles reaching above the toilet seat, leading to large-scale virus spread. Suggestions concerning safer toilet use and recommendations for a better toilet design are also provided.

Although most research suggests that COVID-19 is spread through droplets and contact, the virus has shown up in poop samples and even in sewer systems, so it is likely that there is some fecal-oral transmission. Then the study authors get dramatic:

A confirmed case usually remains at home for isolation, where shared use of a bathroom is inevitable. The daily flow of people in a public washroom is stunningly large: thus, a confirmed case may cause a massive number of infections.

Is This News?

bacteria settle on surfaces
1975: spread of bacteria from flushing toilet.  Charles Gerba et al via  NCBI

It is not to regular Treehugger readers; we have been obsessed with toilets for years, often quoting microbiologist Charles Gerba, lead author of a 1975 study,
Microbiological Hazards of Household Toilets: Droplet Production and the Fate of Residual Organisms. He found that bacteria and viruses remain inside toilet bowls even after repeated flushing, and also get airborne.

The detection of bacteria and viruses falling out onto surfaces in bathrooms after flushing indicated that they remain airborne long enough to settle on surface throughout the bathroom. Thus, there is a possibility that a person may acquire an infection from an aerosol produced by a toilet.

This is why we have always recommended that the toilet not be located in the same room as the sink, and if you don't have the room for that, you should always close the lid on the toilet before flushing, and never leave your toothbrush in an open spot where bacteria or viruses can settle on it.

Gerba actually did study real toilets and real bacteria and viruses, going way beyond a mathematical simulation as done in the new Chinese study. As a 2013 study, Lifting the lid on toilet plume aerosol: A literature review with suggestions for future research, notes, this has all been known for over a century and included studies of coronaviruses. The study authors conclude:

Contaminated toilets have been clearly shown to produce large droplet and droplet nuclei bioaerosols during flushing, and research suggests that this toilet plume could play an important role in the transmission of infectious diseases for which the pathogen is shed in feces or vomit. The possible role of toilet plume in airborne transmission of norovirus, SARS, and pandemic influenza is of particular interest.

But nobody really knows how much of the coronavirus gets airborne, and whether it is in enough of a concentration to infect, or if it is in fact the biggest problem in a bathroom.

Charles Gerba is still looking at this problem forty-five years after his initial study, and still has the same advice: Close the toilet lid. He tells the Washington Post: “I don’t think it’s butt-borne, so I don’t think you have to worry.” Public washrooms are another story; they have no lids and the flush is much more powerful.

In the absence of clear evidence, Gerba said, his advice remains the same: “Flush and run” when using a public toilet without a lid. Wash hands well post-flush and use hand sanitizer after leaving the restroom. Choose well-ventilated bathrooms if possible, and “don’t hang around the restroom” in any case.

Mary Jo DiLonardo of Treehugger has also discussed bathrooms, quoting Gerba on the biggest problem in the bathroom: the towels.

"What happens is, people wash their hands after they go to the toilet. There's always some bacteria left on their hands, which they wipe on the towel. And the towel stays damp," Gerba explains. "You'd get more fecal bacteria on your face if you wiped your face in a hand towel than if you stuck your face in the toilet."

Mary Jo also cautions us that faucets are germy; "When you turn the water on to wash your hands, that contaminates the faucet. When you turn the water off, you recontaminate your hands." This is why hands-free faucets are becoming the standard in public washrooms, and doorless entries.

It's Time to Rethink the Bathroom

maybe they should be outdoors again
Maybe they should be outdoors again like in 1875. Charles Marville/ Getty Images

In the end, there is nothing in the latest toilet plume study that we didn't know already or that we haven't been complaining about a long time. Our current public and private bathrooms are a design disaster, and the fixtures that go in them are just as pathetic. But this has been known for years; perhaps finally, something might be done about it.