PUBLIC toilets pose a high Covid risk due to particles from urination and poo, a grim study has warned.
Scientists say tiny cubicles can be riddled with thousands of virus-containing droplets.
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The droplets are generated when the toilet is flushed – which can happen several times an hour in the busiest of places.
If someone inahles this “toilet plume”, it could cause coronavirus infection, warn the study authors at Florida Atlantic University’s College of Engineering and Computer Science.
They conducted experiments in a typical public toilet using a machine which counts particles at various heights.
The droplets were detected at heights of up to five feet (1.5 metres) for 20 seconds or longer after initiating the flush.
Researchers detected a smaller number of droplets in the air when the toilet was flushed with a closed lid, although not by much.
It suggests that while keeping the lid down while flushing helped, droplets escaped through small gaps between the cover and the seat.
Dr Siddhartha Verma, co-author of the study published in the journal Physics of Fluids, said: “After about three hours of tests involving more than 100 flushes, we found a substantial increase in the measured aerosol levels in the ambient environment with the total number of droplets generated in each flushing test ranging up to the tens of thousands.
“Both the toilet and urinal generated large quantities of droplets smaller than 3 micrometers in size, posing a significant transmission risk if they contain infectious microorganisms.
“Due to their small size, these droplets can remain suspended for a long time.”
The largest increase of particles was in those sized between 0.5 to 1 micrometers, which rose by four-fold.
The droplets are small meaning they are classified as “aerosols”.
Usually aerosols come from someone talking, singing or breathing, for example.
But they can be generated from something like a flush, which propels particles from someone’s faeces or urine into the air.
Urine and faeces have both been found to contain traces of virus particles, as well as vomit.
The World Health Organization says Covid transmission is usually the result of large droplet transmission, caused by coughing.
But aerosols are also thought to play a role. They can linger in the air for long periods of time before settling on surfaces.
What’s more, public toilets are relatively confined, experience heavy foot traffic and may not be ventilated.
Dr Masoud Jahandar Lashaki, co-author, said: “The significant accumulation of flush-generated aerosolized droplets over time suggests that the ventilation system was not effective in removing them from the enclosed space even though there was no perceptible lack of airflow within the restroom.
“Over the long-term, these aerosols could rise up with updrafts created by the ventilation system or by people moving around in the restroom.”
The study suggests that you could prevent risk of catching Covid from a public toilet by wearing a face covering and making sure to wash your hands after leaving it.
Keeping the lid down while flushing will also prevent you from spreading the virus further in the possibility you are unknowingly infected.