Is toilet flushing a COVID-19 risk? Experts say ‘focus on interventions that matter’

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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.”

READ MORE: The coronavirus doesn’t spread easily through contaminated surfaces, CDC clarifies

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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.”

The study has proliferated on social media, with outlets like the New York Times and CNN garnering thousands of retweets.

While the experts welcome scientific research into a virus the world still knows very little about, they emphasize that preliminary, theoretical studies shouldn’t have any bearing on behaviours quite yet.

“People should be prepared to see many of these kinds of studies. Insert whatever you want here — cats, dogs, toilets — anything you want,” said Alon Vaisman, infection control and infectious diseases physician at Toronto’s University Health Network.

“Occasionally, some of these studies will be really critical, but the vast majority will be either not clinically significant or they will not lead you to need to change your behaviour in any significant way.”

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Scientists agree that COVID-19 infections typically happen when a healthy person comes into contact with respiratory droplets from an infected person’s cough, sneeze or breath. The droplets tend to fall to the ground within one to two metres of the person who emits them.

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The study, published in the institute’s journal, Physics of Fluids, focuses on the air movement of contaminated aerosols. The researchers suggest aerosol particles can propel from the toilet bowl at a velocity of five metres per second and those that escape the bowl continue to flow through the air.

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In one test, using a single-inlet flush, the researchers found that around 2,700 particles had sprayed up from the toilet bowl 70 seconds after flushing.

The study also examined differences in types of toilets — a single tank and double tank, or single-inlet and annular. While a toilet with two inlet ports for water generates an even greater velocity of upward-flowing aerosol particles, the researchers say that “without exception, massive upward particle transport is observed for both flushing processes.”

But the problems in evidence about aerosol transmission are aplenty, said Bogoch.

READ MORE: Physical distancing, mask use cuts relative coronavirus risk by at least 80%, study finds

When someone sneezes or coughs, a variety of droplet sizes are generated.

“We often make a false distinction between droplets and airborne transmission and we silo them. In fact, it’s a spectrum,” Bogoch said. “There’s a spectrum of particle sizes that are in the air. The data we have to date demonstrates this is certainly on the droplet end of the spectrum.”

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Even then, it’s unlikely the virus can survive very long in the tiny aerosolized particles, said Vaisman, let alone transmit easily. At this point in the pandemic, the infectious disease community isn’t concerned with aerosol transmission as they may have been in the very beginning, he added.

“It’s not to say it doesn’t happen. It’s that it’s not driving the pandemic and it’s not likely to be a major source of infection,” he said. “That’s why we don’t use N95 masks, for example, when we look after patients with COVID-19 right now.”

It’s not the first time feces has been tied to COVID-19 research. Some studies have suggested that the virus can survive in the human digestive tract and show up in fecal matter.

One study, published in March in the journal Gastroenterology, found significant amounts of COVID-19 in the stool of patients — even long after the virus cleared from the person’s respiratory tracts, in some cases. Sewage is also now being studied to track how the virus might spread.

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In fact, the transmission of illnesses through fecal matter is nothing new, Vasiman said. Bathrooms — or fecal-oral transmission — are known to contribute to the spread of diseases like the norovirus.

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Typically, the coronavirus is found in cells in the lungs and throat, but the new study notes “some patients have developed gastrointestinal symptoms such as diarrhea and vomiting, showing that the virus can survive in the digestive tract.”

It’s not definitive whether public or shared toilets are a common point of transmission for COVID-19, but the risk is “extremely low” at this point, said Vaisman.

READ MORE: Canada is one of few countries 2-metre distancing. Experts say reducing is ‘risky’

The study authors ultimately suggest that, whenever possible, people should keep the toilet seat down when flushing. They also encourage cleaning the seat and other high-contact areas in the bathroom, as well as washing your hands after using the toilet.

That advice is long-standing, said Bogoch, with or without a pandemic.

“Is flushing the toilet with the seat open going to truly result in the measurable increase in the number of new cases of COVID-19? The answer is most certainly no,” he said.

“Should you close the lid of the toilet before your flush for many, many reasons — mainly courtesy? Yes. Full stop.”

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