Researchers are getting closer to understanding how COVID-19 is transmitted in public.

A research team at Yangzhou University in China found that a cloud of aerosol droplets from a flushed toilet can spray as high as 3 feet in the air and potentially spread COVID-19.

The researchers used a computer simulation to figure out how far the droplets can travel for a study published Tuesday in the journal Physics of Fluids. If droplets stick around in the air for long enough, they can be inhaled by the next person to use the toilet or on other surfaces in the bathroom, according to the New York Times. The aerosol cloud can also carry infectious droplets from the air nearby or from a person’s stool. 

“One can foresee that the velocity will be even higher when a toilet is used frequently, such as in the case of a family toilet during a busy time or a public toilet serving a densely populated area,” Ji-Xiang Wang who co-authored the study said in a news release.

Keeping bathrooms clean and sanitized at all times is a big challenge, Wang told the New York Times.

It is still unknown how big of a role public and shared toilets play in the spread of COVID-19, but the study highlights the need to assess the threats of communal areas, especially as areas begin to lift stay-at-home orders.

Experts not affiliated with Yangzhou University say the study is critical to helping prove why better action is necessary to prevent the spread of COVID-19, according to the New York Times.

More data on how aerosol clouds transmit the virus is crucial to protecting people living in poverty, who are more likely to be exposed to the spread of disease without proper water and sanitation. More than 4.2 billion people lack safely managed sanitation services and have no choice but to use inadequate toilets or practice open defecation. 

Closing the toilet lid before flushing would mitigate the problem, but in many countries around the world, public toilets and latrines cannot be closed. Toilets that automatically shut after flushing could be one solution, according to the study’s authors.

In the meantime, Wang recommends people continue to wash their hands efficiently, avoid touching their faces, and keep a mask on, even in shared bathrooms. 

Water and sanitation advocates have been pushing to install sustainable toilets in developing countries to prevent the spread of disease long before the COVID-19 pandemic. Wang hopes his research contributes to positive changes in bathroom design to promote safer hygiene.