Wearing a mask in public restrooms should be mandatory during the pandemic, researchers say, because there’s increasing evidence that flushing toilets – and now urinals – can release inhalable coronavirus particles into the air.
The coronavirus can be found in a person’s urine or stool, and flushing urinals can generate an “alarming upward flow” of particles that “travel faster and fly farther” than particles from a toilet flush, according to a study published in the journal Physics of Fluid Monday.
“Urinal flushing indeed promotes the spread of bacteria and viruses,” researcher Xiangdong Liu said in a press release. “Wearing a mask should be mandatory within public restrooms during the pandemic, and anti-diffusion improvements are urgently needed to prevent the spread of COVID-19.”
Liu and other researchers from Yangzhou University in China simulated urinal flushing using computer models and estimated that, within just five seconds of flushing, virus particles could reach a height of more than 2 feet off the ground.
“Potentially, it could contaminate other surfaces you would touch – the handle, the tap,” said Charles Gerba, a professor of virology at the University of Arizona. “The concern is also – was there anything left over from the person who was there before? Aerosolization from the previous user you may potentially inhale?”
Some of the same researchers released similar findings in June, focused on toilet flushing. Through another computer model, the researchers found that thousands of particles can come out of the toilet within 70 seconds of flushing, and that some can reach higher than a foot above the toilet bowl in half that time.
“It is reasonable to assume that the high-speed airflow will expel aerosol particles from the bowl to regions high in the air above the toilet, allowing viruses to spread indoors causing risks to human health,” the researchers said at the time.
The studies are interesting but unsurprising, as research on particles kicked up in “toilet plumes” has been around for about two decades now, said Joshua Santarpia, a professor of pathology and microbiology at the University of Nebraska Medical Center specializing in bioaerosols.
“The more interesting thing to me was that I hadn’t considered the urine issue – whether SARS-CoV-2 was shed in urine,” he said.
Coronavirus found in urine, stool
Many people aren’t aware that toilets and urinals can release particles into the air, let alone that genetic material from SARS-CoV-2 – the virus that causes the disease known as COVID-19 – can be found in patients’ urine and stool, Gerba said.
“It’s probably been overlooked – urine contamination,” Gerba said. “Smallpox, Zika virus are excreted in the urine. What’s surprising is that a respiratory virus can be excreted in the urine.”
At least two studies – one in Tokyo and one in Guangzhou, China – have found coronavirus RNA in patients’ urine. Studies published in the journals Gastroenterology and The Lancet also found coronavirus RNA in patients’ stool, even weeks after the patients showed negative results in respiratory samples. One study in and around Beijing, however, did not find any evidence of virus in 72 urine specimens.
It’s still unclear whether COVID-19 can transmit through urine and infect another person, Gerba said.
“Is there enough virus in the urine to worry about? Does enough get aerosolized? Those are questions we need to look at,” he said.
The researchers at Yangzhou University argue that transmission in a public restroom has already happened. They cite local news reports of a couple, who work at a food market in Beijing, contracting the virus at a restroom nearby.
“What’s worse, two of COVID-19 reemerging confirmed cases in Beijing have been reported to be infected from a public toilet, which practically proves the danger from the public restroom,” the researchers wrote.
Can the coronavirus disease spread through air?
Health experts believe the virus mainly transmits through respiratory droplets when someone coughs or sneezes, but the World Health Organization says that “short-range aerosol transmission . . . cannot be ruled out.”
Researchers measuring the amount of viral aerosols in different areas of two Wuhan hospitals found that while the concentration detected in isolation wards and ventilated patient rooms was very low, it was higher in the toilet areas used by the patients, according to an April study published in the journal Nature.
The researchers recommended that room ventilation, open space, sanitization of protective apparel, and proper use and disinfection of toilet areas could effectively limit the concentration of SARS-CoV-2 RNA in aerosols.
“I think there’s a lot of strategies and interventions that could be developed if it really turns out that there’s significant risk,” Gerba said.
For now, the next best step would be to put the researchers’ computer model to the test to see if flushing a urinal actually kicks virus particles up into the air, Gerba and Santarpia said.
“Somebody should really validate some of this experimentally. It’s a model, and there are a lot of assumptions,” Santarpia said. “More work needs to be done.”
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