Preventing viral spread in the restroom and why closing the lid is not enough

March 18, 2024

Environmental science researchers at UArizona explored the potential health hazards hidden in toilets and what people can do to mitigate risks in the restroom.

Dr. Charles Gerba examines a sample under a microscope in a University of Arizona lab

Environmental Science professor Charles Gerba researches restroom germs at the Water and Energy Sustainable Technology (WEST) Center.

It’s no mystery that what we flush down the toilet is full of germs, but University of Arizona researchers are interested in the viruses that are coming back out.

Charles Gerba, a professor in the Department of Environmental Science at UArizona, recently found that viral pathogens in human waste can be spread via toilet flush, even when the toilet seat is closed. 

Dr. Charles Gerba headshot from the University of Arizona

Charles Gerba is a professor in the Department of Environmental Science who researches microbiology at the Water & Energy Sustainable Technology Center (WEST).

“Closing the toilet doesn’t really do what we thought it did,” Gerba said. “The air is forced out sideways, so you get aerosol coming out between the toilet seat and the cover.”

Using simulated public and household restroom environments at the Water and Energy Sustainable Technologies (WEST) Center, Gerba added a sample virus to toilet bowls and recorded its spread to surrounding surfaces after a flush. 

While bacteria spread is limited by a closed toilet seat lid, viral particles are small enough to spread to surrounding surfaces, contaminating the floor, toilet lid and adjacent walls. 

Since closing the toilet does not stop viral spread, Gerba suggested other measures for limiting health risks in the home. His study found that effectively cleaning toilets with both a disinfectant and brush reduced contamination in the toilet water by 99.99 percent. 

“What you really should do is try to clean and disinfect the restroom about every three days with multiple products,” Gerba said. “There’s a lot of products now that are a lot more convenient and a lot more effective than they used to be, and a lot more environmentally friendly too.” 

Gerba’s research also examined viral spread in private restrooms compared to public restrooms, finding public toilets exhibit a greater degree of restroom contamination than private ones.

Contributing factors to the difference in contamination, according to Gerba, were a higher water volume in the public toilet and its U-shaped seat, versus the lower water volume and circular seat of the private toilet.

While public restrooms see more contamination, Gerba said they are typically cleaned more often than private ones. He aims to use this research to improve household disinfection practices and limit health risks in the home.

“We know that home restrooms are germier, but we want to quantify it to really inform the public,” Gerba said. “What we’re after is how we can reduce the risk of people getting ill in a restroom — home or public.”

In the future, Gerba plans to continue his research on quantifying viral spread in the restroom, potentially focusing on aspects of the restroom such as variations in global toilet designs and lasting effects of different disinfectants.