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Coronavirus: pathogens linger in toilet for hours if you flush without closing lid – and some may still sneak through even if it is down, Hong Kong study finds

  • Polluted droplets can follow air flow and be carried to other rooms in a home
  • Running exhaust fan for 15 minutes will remove vast majority of airborne pathogens, study leader says

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Professor Alvin Lai of City University of Hong Kong explains the relationship between flushing the toilet and the transmission of pathogens on February 13. Photo: K.Y. Cheng

A toilet flush can release up to 80,000 polluted droplets and leave them suspended a metre in the air for hours if the lid is left up, a new study has found.

The findings, released by City University’s Department of Architecture and Civil Engineering on Thursday, also revealed smaller bacteria are even more likely to become airborne and transmitted into the surrounding area via droplets produced in flushing. Smaller agents still, such as the deadly coronavirus now confronting Hong Kong, may also spread through the water particles.

Alvin Lai Chi-keung, associate head of the department who led the year-long study, said while water droplets created in flushing might rise up to a metre if the toilet was not covered, international studies suggested polluted particles may still sneak through the gaps between the toilet and its lid, even if it was lowered before flushing.

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Dr Eric Lee (left) and Professor Alvin Lai of City University and infectious disease expert Dr Iris Li explain the distribution of airborne aerosol droplets emitted from toilet flushing on February 13. Photo: K.Y. Cheng
Dr Eric Lee (left) and Professor Alvin Lai of City University and infectious disease expert Dr Iris Li explain the distribution of airborne aerosol droplets emitted from toilet flushing on February 13. Photo: K.Y. Cheng

“Covering the toilet lid while flushing is definitely essential, but it should not be considered a complete prevention,” he said.

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Lai said he was not intending to add to public fear amid the outbreak of Covid-19, the disease caused by the new coronavirus, as his study was begun years ago.

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