New research on the aerosolization of pathogens provides recommendations for public restroom use. According to the study published in the journal Physics of Fluids, flushing a toilet can disperse aerosols with microbes that can cause a range of illnesses, such as Ebola, COVID-19, and food poisoning induced by norovirus. The study calls for the proper ventilation of public restrooms as well as the installation of toilet lids to decrease the spread of pathogens through flushing.
Conducted by a team of scientists from Florida Atlantic University's College of Engineering and Computer Science, the study takes a fluid dynamics angle to investigate the movement through air of droplets generated from flushing a toilet/ urinal in a public restroom with typical ventilation conditions. Using a particle counter, the researcher collected data on the size and number of droplets generated upon flushing in three scenarios: toilet flushing; covered toilet flushing and urinal flushing.
"After about three hours of tests involving more than 100 flushes, we found a substantial increase in the measured aerosol levels in the ambient environment with the total number of droplets generated in each flushing test ranging up to the tens of thousands," elaborates co-author of the study Siddhartha Verma, Ph.D., who is an assistant professor in FAU's Department of Ocean and Mechanical Engineering. "Both the toilet and urinal generated large quantities of droplets smaller than 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."
The study points towards the lack of ventilation in public restrooms as well as the risk posed by restrooms without toilet lids (as are most in the United States). "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," said co-author Masoud Jahandar Lashaki, Ph.D., who is an assistant professor in FAU's Department 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."
The authors warn that public restrooms could be perpetuating the transmission of airborne diseases, given that microbes can remain suspended in particles for several hours. "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," concludes study co-author Manhar Dhanak, Ph.D. "The good news is that it may not always be necessary to overhaul the entire system since most buildings are designed to certain codes. It might just be a matter of redirecting the airflow based on the restroom's layout."