Don't remove face masks in toilets, scientists warn

People are being warned not to remove face masks when in public toilets and closed spaces such as elevators after a study found that people can easily contract the novel coronavirus while using these facilities.

The study, conducted by a team of researchers led by Chulabhorn Research Institute researcher Kwanrawee Sirikanchana, found that using public toilets may increase the risk of Covid-19 via airborne transmission.

The study, published in the Journal of Water and Health, focused on the effects of face masks and ventilation and the risk of Covid-19 respiratory transmission in public toilets.

It looked at scenarios where an individual used a public toilet after a Covid-19 infected person. One involved neither of them wearing a face mask and others where they both wore N95 or surgical face masks.

The study found that without face masks, there was a 10% risk of being infected, but the risk increased to almost 100% if the Covid-19 infected person coughed or sneezed in the toilet. However, if both wore face masks, the risk was just 0.01%. According to the study, a 10-minute wait time could also reduce the risk of being infected, but face masks offered the best protection.

Thammanitchpol Denpetkul, a lecturer at the faculty of tropical medicine, Mahidol University, said the virus can be transmitted via droplets and aerosols even smaller than PM2.5 dust particles.

He said respirators such as N95, KN95, KF94 and FFP2 offer the most effective protection when using public toilets while surgical masks are the second-best option.

"Some cloth masks may not be good enough to protect against the virus ... but if someone uses an N95 mask and wears it properly, the risk is one in 100,000," he said.