Can You Get Sick from the Germs in Toilet Plumes?

The Washington Post / Lindsey Bever

12:50 JST, August 19, 2024

The question:

Is it true that there’s an invisible plume of pathogens that spews out of the toilet when you flush it – and that it can make you sick?

The science:

When you flush a toilet, aerosols containing any pathogen residing in the bowl spray into the bathroom.

A 2022 study that used lasers to illuminate these aerosolized plumes found that the plumes, which may contain bacteria and viruses, can shoot almost five feet into the air – the approximate height of the nose and mouth of an average adult – within about eight seconds of the flush, said John Crimaldi, a professor of civil, environmental and architectural engineering at the University of Colorado at Boulder, who was the lead author of the study.

The plume also spread several yards horizontally within a short time, Crimaldi said.

“We were able to see it spread across a fairly large lab in the span of minutes,” he said. “If you’re in a large, public restroom that has a dozen stalls, there’s a dozen plumes spreading throughout there constantly.”

The largest particles, which can be as big as droplets, can land on nearby surfaces and items such as a towel or toothbrush almost immediately, but the smallest ones can stay airborne for “tens of minutes,” Crimaldi said. Air flow can then blow the particles through the room.

“By the time the next user goes into the toilet stall, certainly that plume is still present,” Crimaldi said.

But it is unlikely for most people to become infected by pathogens in the plume unless someone with a highly contagious disease such as the stomach bug norovirus previously used the toilet, said Katrin Kuhn, an infectious-disease epidemiologist who is also an associate professor and vice chair of the department of biostatistics and epidemiology at the University of Oklahoma Health Sciences.

Bacteria and viruses can live on certain surfaces from hours to weeks but, to become infected, a person would have to inhale or ingest what is called an infectious dose, which varies from one pathogen to the next. For instance, with shigella, a gastrointestinal bacteria, it may take 10 organisms to cause illness, whereas with salmonella, it would take more than 50,000, research shows.

A 2013 literature review reported that while infectious aerosols may be produced by flushing a toilet, no study has proved that toilet plumes lead to infection.

“That’s why you don’t see public health advisories about making sure the lid is down before you flush,” said William Schaffner, a professor of infectious diseases and preventive medicine at Vanderbilt University.

The risk from the organisms on your hands is much higher than from the organisms in the toilet plume, experts said. When you touch surfaces, including doorknobs, elevator buttons and shopping carts, you can pick up pathogens and then, when you scratch your nose or wipe your mouth, you can become infected.

What else you should know:

Studies have shown that closing the toilet lid before you flush does reduce the number of particles that are ejected into the air, but it does not eliminate them. One study reported that the lid reduced the total concentration of particles by 48 percent, and total surface area concentration by 76 percent.

Typically, there are spaces between the toilet lid and the seat as well as between the seat and the bowl. These spaces redirect “the energy in the plume to be more horizontal rather than vertical,” Crimaldi said. It changes the distribution, but closing the lid “certainly does not eliminate the plume,” he added.

Another study also reported that closing the lid did not reduce viral contamination of other bathroom surfaces.

Good hand hygiene is among the most effective ways to protect against infection, Kuhn said.