If you’re in a public restroom, you may not want to hang around too long, because lots of airborne pathogens are hanging around, too.

Researchers from Florida Atlantic University’s College of Engineering and Computer Science conducted flush tests in a public restroom with both a toilet and a urinal.

“After about three hours of tests involving more than 100 flushes, we found a substantial increase in the measured aerosol levels … with the total number of droplets generated in each flushing test ranging up to the tens of thousands,” said study co-author Siddhartha Verma. He is an assistant professor of ocean and mechanical engineering at the university.

Pathogens that can cause Ebola, norovirus and even COVID-19 can be found in stagnant water, as well as in urine, feces and vomit. According to the research team, flushing can generate large amounts of airborne germs, depending on flushing power, toilet design and water pressure.

For the study, the researchers placed a particle counter at various heights of the toilet and urinal to capture the size and number of droplets generated by flushing. They did the same with a covered toilet. (Few public restrooms in the United States have lids, and urinals are not covered.)

Droplets were detected at heights of up to 5 feet for 20 seconds or longer after initiating a flush, the findings showed.

The investigators detected fewer droplets when the lid was closed before flushing, but the number wasn’t much less. This suggests that aerosol droplets escaped through small gaps between the cover and the seat.

Verma noted that both the toilet and urinal generated large quantities of droplets under 3 micrometers in size, posing a significant transmission risk if they contain infectious microorganisms.

“Due to their small size, these droplets can remain suspended for a long time,” Verma explained in a university news release.

The researchers reported a 69.5% increase in measured levels of particles between 0.3 and 0.5 micrometers in size; a 209% increase for particles sized 0.5 to 1 micrometer; and a 50% increase for particles between 1 and 3 micrometers.

According to study co-author Masoud Jahandar Lashaki, “The significant accumulation of flush-generated aerosolized droplets over time suggests that the ventilation system was not effective in removing them from the enclosed space even though there was no perceptible lack of airflow within the restroom.” Lashaki is an assistant professor of civil, environmental and geomatics engineering.

“Over the long-term, these aerosols could rise up with updrafts created by the ventilation system or by people moving around in the restroom,” he explained.

Even larger aerosols can add risk, the study authors noted.

Co-author Manhar Dhanak, chairman of ocean and mechanical engineering, pointed out that the study suggests that “incorporation of adequate ventilation in the design and operation of public spaces would help prevent aerosol accumulation in high-occupancy areas such as public restrooms.”

The restroom was deep cleaned and closed 24 hours before conducting the experiments, and the ventilation system was operating normally.

The report was published recently in the journal Physics of Fluids.

Stella Batalama is dean of engineering and computer science at the college. She concluded that “aerosolized droplets play a central role in the transmission of various infectious diseases including COVID-19, and this latest research by our team of scientists provides additional evidence to support the risk of infection transmission in confined and poorly ventilated spaces.”

More information

The U.S. Centers for Disease Control and Prevention has more on COVID-19.

SOURCE: Florida Atlantic University, news release, April 20, 2021

Source: HealthDay