New Study Shows Toilet-Related Coronavirus Transmission Risk

While the toilet plume effect has been studied for decades in relation to other diseases, many questions remain over its role in spreading germs, including the one that causes COVID-19.

Another day, another COVID-19 study. This time, the focus is on the toilet — and what we do when we’re finished using it.

Researchers from the American Institute of Physics modelled the amount of droplets that can be created by flushing a toilet.

They suggest that the “turbulence” caused by flushing can fling droplets nearly one metre above the bowl, where they might be inhaled or rest on surfaces, leading to possible transmission of the coronavirus.

The droplets, they say, are so small that they float in the air for more than a minute, leaving ample time to either come in contact with the toilet seat or the person using it.

Experts call it a “toilet plume.”

Canadian infectious disease experts, however, are unconvinced about the likelihood someone could catch the virus this way.

“If everyone starts putting the seat down when they flush, is this going to have any meaningful impact, locally or globally? It will not,” Isaac Bogoch, an infectious disease specialist based out of Toronto General Hospital.

“Focus on interventions that actually matter, like hand hygiene and physical distancing and mask-wearing.”

Such worries came to a head this week when researchers in China published a study suggesting that flushing a toilet can create a plume of coronavirus-laden particles, which are flung into the air by the watery vortex inside a toilet bowl.
Several studies using genetic tests have previously detected the SARS-CoV-2 virus in stool samples, and at least one investigation shows that the coronaviruses in these feces can be infectious.

When a person infected with COVID-19 defecates, the germ at first settles into the toilet bowl.

But then “the flushing process can lift the virus out of the toilet and cause cross-infection among people,” says Ji-Xiang Wang, a physicist at Yangzhou University in China and coauthor on the paper published June 16 in the journal Physics of Fluids.

While the toilet plume effect has been studied for decades in relation to other diseases, many questions remain over its role in spreading germs, including the one that causes COVID-19.

Neither the World Health Organization nor the U.S. Centers for Disease Control and Prevention thinks it’s very likely COVID-19 can be spread by bowel movements leading to accidental consumption of virus particles, a route medically termed fecal-oral transmission.

Despite these uncertainties, experts say there are precautions you should take before answering nature’s call in publicly shared restrooms.

Toilet-Related Risk: How risky are restrooms?

For the latest study, Wang’s team used computer models to show that tiny droplets called aerosols, created by the turbulence of water sloshing inside a toilet bowl, could be ejected up to three feet into the air.

Shortly after flushing, water rushes into the bowl, striking the opposite side with enough force to generate a vortex that forcefully pushes not only the liquid, but also the air inside the toilet.

According to their simulations, this combination launches aerosols that can last in the air for just over a minute. The more water used in a toilet bowl, Wang’s team found, the greater the force of the flush.

So what does that mean if you use a restroom after someone infected with COVID-19 flushes? That depends a lot on whether the infectious virus survives in human feces, and that’s still an active area of research.

To start, studies of MERS, a coronavirus relative that flared up in 2012, indicate that this particular virus can survive in the human digestive tract, which is a sign the same might be true for SARS-CoV-2. Flu viruses and coronaviruses are considered “enveloped viruses” because they’re protected by a thin layer called a membrane.

Unlike noroviruses, the most common culprit of food poisoning, enveloped viruses are easily degraded by acids, which make them vulnerable to the chemical make-ups of soap and stomach bile.

One hypothesis, based on influenza research, suggests that these kinds of viruses might survive in the human gut if mucus from infected patients protects the germs during their journey through the digestive tract. The question then is how long the virus lasts in fecal matter, and that’s another area that needs more research, says E. Susan Amirian, a molecular epidemiologist at Rice University in Houston.

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