What We Actually Know About How COVID Spreads in Bathrooms

In the early, dark days of the pandemic, when we knew almost nothing and feared almost everything, there was a moment when people became seriously concerned about toilets. More specifically, they were concerned about the possibility that latrines’ cloud of particles in the air at flushes — known in the scientific literature as a “toilet plume” — could be an important factor for COVID transmission. Since the coronavirus can be found in human excrement, “flushing the toilet may spew coronavirus sprays everywhere,” she said. New York times He warned in June 2020. Every now and then in the years since, occasionally PSA From a scientist or public health expert who renewed the scattered panic.

In retrospect, much of what we thought we knew in those early days was wrong. Lysoling our groceries turned out to be unhelpful. Masking turned out to be very helpful. Although hand washing is still important, it wasn’t all it was cracked up to be, and herd immunity was, after all, a mirage. As the country transitions into post-pandemic life and takes stock of the past three years, it’s worth asking: What’s the real deal with a toilet bowl?

The short answer is that our fears aren’t vindicated, but they aren’t fully exaggerated either. Scientists have been studying the toilet bowl for decades. They found that the columns varied in size depending on the type of toilet and flushing mechanism. flush energy It also plays a role: the larger it is, the larger the column. Sealing the lid (if your toilet has one) helps a lot, although this can’t completely eliminate the toilet plume – particles can still escape through the gap between the seat and the lid.

Whatever the details, the main conclusion from years of pre-pandemic research is both consistent and disgusting: “Flush toilets produce large amounts of toilet plume spray capable of attracting microorganisms at least the size of bacteria…these bio-aerosols may still be viable in air for extended periods and travel with air currents,” scientists at the CDC and the University of Oklahoma School of Public Health wrote in a 2013 review paper titled “Lifting the Lid on Bloom Toilet Sprays.” In other words, when you flush the toilet, an unsteady amount of contents goes up instead of down.

Knowing this is something. Seeing it is another. Traditionally, scientists have measured a toilet’s plume with either a particle counter or, in at least one case, a “computational model of an ideal toilet.” But in a new study published last month, researchers at the University of Colorado at Boulder took things a step further, using green-light lasers to make what, fortunately, not normally visible. John Crimaldi, an engineering professor and study co-author who has spent 25 years using lasers to illuminate invisible phenomena, told me that he and his colleagues went into the experiment fully expecting to see something. However, they were “completely surprised” by the results. The plume was bigger, faster, and more energetic than they had expected — “like a volcanic eruption,” Crimaldi said, or, as he and his colleagues described it in their paper, “a powerful anarchic jet.”

Within eight seconds, the resulting aerosol cloud shoots five feet above the toilet bowl—more than six feet above the ground. This is it: straight in your face. After the initial explosion, the plume continues to rise until it reaches the ceiling, then shoots out. It meets a wall and runs along it. Before long, the room fills up. Once that happens, it hangs around for a while. “You can kind of extrapolate in your mind to stepping into a public toilet in an airport that has 20 toilets, and they all flush every two minutes,” Crimaldi said. Not a fun idea.

The question then is not so much whether the toilet plume is happening — like it or not, as it obviously is — but whether it is a legitimate transmission risk of COVID or something else. This part is not very clear. A 2013 review paper identified studies of the original SARS virus as “among the most compelling indications of the potential for transmission of airborne disease by toilet flushes”. (The authors also note, dryly, that although SARS “was not currently a common disease, it demonstrated its potential for explosive spread and high mortality rate.”) One such study that the authors discuss explicitly is a report on the 2003 outbreak in Amoy Gardens apartment complex in Hong Kong. This study, though, is not conclusive, Mark Sopsey, an environmental microbiologist at the University of North Carolina at Chapel Hill, told me. The researchers did not rule out other routes of transmission, nor did they attempt to culture live virus from feces — a more reliable indicator of infection than mere detection.

Moreover, Sopsi said, there is little evidence that toilet flushes spread SARS or COVID-19. In his own review, published in December 2021, Sobsey found “no documented evidence” of fecal transmission of the virus. This, at least, seems to be tracing back three years of pandemic experience that we’ve all endured now. Although we can not prove that the bathrooms easily no It plays a significant role in the spread of COVID-19, and we haven’t seen any clear indications of that Do. And anyway, the coronavirus has found plenty of other horrible ways to spread.

Just because a toilet bowl doesn’t appear to be a vector for COVID transmission, though, doesn’t mean you can forget about it. Digestive viruses, such as norovirus, present a more serious risk of transmission via the toilet bowl, Subsi told me, because they are known to spread via feces. The only real solutions are structural solutions. Improved ventilation will prevent the build-up of volatile waste in the air, and germicidal lighting, although the technology continues to be developed, could disinfect what remains. However, neither of them would stop the column in the first place. To do this, you’ll need to change the toilet itself: In order to create a smoother flow and thus a better fit, you can change the geometry of the bowl, the way the water enters and exits, or any number of other variables. Toilet manufacturers could also, you know, stop producing toilets without a lid.

But none of this will save you the next time you find yourself staring into a vacant toilet. Creamdy suggests wearing a mask in public bathrooms to protect not only from plume from cleaning but also from plume left by the person who used the bathroom before you, the person who used it before them, etc. You don’t need to have any major craving for disguise as a public health intervention to consider wearing one for a few minutes to avoid literal breathing. Subsi offered another unorthodox piece of bathroom hygiene advice, which he concedes can do little to protect you: If you find yourself in a public restroom with a toilet without a lid, consider washing your hands. before You flow. Then “hold your breath, flush the toilet, and let go.”


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