Updated: April 26, 2021 4:24:42 pm
Flushing a toilet generates aerosols that could linger in the air for hours, possibly days. Given that aerosols are now widely accepted as the primary mode of transmission of SARS-CoV-2, the virus that causes Covid-19, is there a risk of getting infected with Covid-19 — or any other respiratory disease — from aerosols generated by a toilet flush? A new study has found that public restrooms can indeed be hotbeds for transmission of airborne diseases.
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But does the coronavirus spread through faecal content or urine droplets?
The evidence so far is limited. Studies have found traces of coronavirus in the gastro-intestinal tract of Covid-19 patients, and in sewage, but there is no conclusive evidence of infection taking place through from faeces, according to the World Health Organization (WHO). “There is some evidence that Covid-19 infection may lead to intestinal infection and be present in faeces… There have been no reports of faecal-oral transmission of the Covid-19 virus to date,” the WHO said in a scientific brief in March last year.
So, has the new study found evidence?
Published in the journal Physics of Fluids, the study did not look at virus content. It measured the quantity of aerosols generated by flushing a toilet. The authors agree that the likelihood of infection for respiratory illnesses via bioaerosols is low, but write that it presents a viable transmission route, especially in public restrooms which often experience heavy foot-traffic within a relatively confined area. A variety of pathogens are usually found in stagnant water as well as in urine, faeces and vomit.
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“I would say that the chances of getting Covid-19 from flush-generated droplets are small. It is much more likely that the respiratory aerosols being exhaled by an infected person breathing within a poorly ventilated restroom pose a much greater threat,” co-author Siddhartha Verma from the Florida Atlantic University said by email.
“Furthermore,” he said, “studies by other groups (cited in our paper) have discussed evidence that flush-generated droplets do pose a notable risk for the transmission of certain gastro-intestinal illnesses.”
What are the findings?
To measure droplets, the researchers used a particle counter placed at various heights of the toilet and urinal to capture the size and number of droplets generated. They collected data from there settings — toilet flushing, covered toilet flushing, urinal flushing — and measured ambient aerosol levels before and after conducting the experiments.
After about three hours of tests involving more than 100 flushes, the team found a substantial increase in the measured aerosol levels in the ambient environment. The total number of droplets generated in each flushing test ranged up to the tens of thousands.
Droplets were detected at heights of up to 5 feet for 20 seconds or longer after initiating the flush. The droplets actually lingered much longer than 20 sections. Beyond the 20-second duration, the droplets will have moved past the detector location and dispersed widely in the room, Verma said.
Researchers detected a smaller number of droplets in the air when the toilet was flushed with a closed lid. But the difference was not much, suggesting that aerosolised droplets escaped through small gaps between the cover and the seat.
There was a 69.5% increase in measured levels for particles sized 0.3 to 0.5 micrometres, a 209% increase for particles sized 0.5 to 1 micrometres, and a 50% increase for particles sized 1 to 3 micrometres.
What are the implications?
The authors stress the importance of adequate ventilation in the design and operation of public spaces such as public restrooms.
“I’d say the main point of this observation is that there was a substantial increase in overall background droplet numbers circulating within the restroom after conducting the flushing experiments,” Verma said. “This is essentially what would happen within a public restroom which is in normal use, and if the ventilation systems are not able to remove and filter out the droplets effectively.”
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