Closing the Toilet Lid Won't Stop Viral Particles From Spreading

Closing the toilet lid before flushing doesn’t reduce the spread of viral particles, according to a new study published on January 24 in the American Journal of Infection Control. Researchers found the only effective way to reduce viral particles was through disinfection of the toilet, toilet water, and nearby surfaces.

Does that mean that closing the lid before flushing is a waste of time? Not necessarily. Even though it didn’t reduce the spread of viruses, closing the lid may prevent the spread of bacteria, says the senior author, Charles P. Gerba, PhD, a professor of virology at the University of Arizona in Tucson.

What Happens When You Flush

When you flush the toilet, millions of aerosolized particles invisible to the naked eye are rapidly ejected into the air. This “toilet plume” can launch those particles five feet or more up and away from the bowl. If contagious germs land in the toilet bowl because you’re sick, flushing can spread them to floors, walls, sinks, and other nearby surfaces in a bathroom, according to the authors.

Researchers Found That Closing the Lid Before Flushing Didn’t Reduce the Spread of Viral Pathogens

Prior studies found that closing the toilet lid reduced the spread of bacteria, but it’s been unclear whether the same is true for viral pathogens, which tend to be much smaller than their bacterial counterparts.

Investigators analyzed the spread of viral particles caused by flushing with toilet lids open and closed to determine whether there was any difference in outcome. They used a virus that is not harmful to humans as a proxy for more dangerous viruses, and seeded toilets with varying doses of it, flushed, and then collected samples from the toilet bowl water as well as surfaces on the toilet, floor, and walls.

In a separate analysis of the effectiveness of cleaning the toilet with a disinfectant, samples were collected from the toilet bowl brush and its caddy. The study included both household and public toilets, but the impact of toilet lid closure could only be studied with the household toilet, since public toilets typically do not have lids.

In the experiments using the household toilet, the researchers found no statistical difference in the amount of virus collected from surfaces on the toilet or the nearby floor whether the toilet was flushed with the lid up or down. Viral contamination of the surrounding walls was minimal in both cases, while the toilet seat was the most contaminated surface. The pattern of contamination was similar for the public toilet, they noted.

Interestingly, closing the toilet lid may alter the direction of the aerosol plume. In closed-lid flushing, floor surfaces in front of and to the left of the toilet were more contaminated and floor surfaces to the right of the toilet were less contaminated, compared to flushing with an open lid.

Why Viral Particles Escape the Toilet Lid

Why do viral particles still escape the toilet lid, but bacterial particles don’t? “Bacteria are much larger than viruses and tend to be associated with larger droplets, which do not remain airborne as long or travel as far. Basically, viruses aerosolize more readily than bacteria,” says Ferric Fang, MD, a researcher and professor at UW Medicine in Seattle who was not involved in the study.

Scientists also examined the effects of cleaning the toilet, both with and without disinfectant. Cleaning with only the brush left behind substantial contamination, but cleaning the toilet bowl with a disinfectant and brush significantly reduced the amount of virus found in the toilet.

Adding disinfectant to the toilet bowl before flushing or using disinfectant dispensers in the toilet tank were both effective ways to reduce contamination from flushing. A disinfectant and brush reduced viral contamination on the toilet by more than 99.99 percent and on the brush by 97.64 percent, according to the findings.

Here’s How Often You Should Clean Your Toilet

These findings can also be used to reduce the spread of nasty germs in the home, according to the authors. “We found that cleaning and disinfecting the toilet twice a week is best to limit the spread of viral particles,” he says.

But if someone in a household is sick, particularly with gastroenteritis (commonly called stomach flu), cleaning and disinfecting one or twice a day is a good idea, says Dr. Gerba. “We also recommend using disinfecting wipes on the toilet seat and flush handle, as these surfaces will get contaminated after flushing,” he adds.

How Often Do Pathogens From Toilet Flushing Make People Sick?

It’s hard to know how often pathogens from toilet flushing make people sick, says Dr. Fang. “There have been some outbreaks of viral gastroenteritis associated with planes or ships in which using a bathroom was a risk factor for acquiring infection. Also, a cluster of SARS cases in a Hong Kong apartment complex in 2003 was attributed to the generation of toilet aerosols that were carried to other apartments by the ventilation system,” he says.

It’s still uncertain whether toilet aerosols in public bathrooms are a significant route for COVID-19 transmission, says Fang. Simulations have shown that toilet plumes can carry viruses recently shed in a person’s stool, including SARS-CoV-2, norovirus and influenza.

Expert Advice on Reducing the Risk Posed by Toilet Plume Germs

Viruses that cause diarrhea have to be swallowed, not inhaled, says Fang. “Flushing the toilet can spread these viruses to bathroom surfaces, where they can be picked up on your hands and transferred to your mouth. Disinfecting bathroom environmental surfaces and careful handwashing with soap and water after using the toilet can prevent this from happening,” he says.

As far as COVID-19 is concerned, the most recent COVID vaccine, a face mask, handwashing with soap and water, abstaining from mobile phone use in the restroom, and spending as little time there as possible will minimize the risk, says Fang.