A woman wearing a protective face mask walks past the European Commission headquarters as the spread of the coronavirus disease has the spread continues across Belgium

Covid-19 can linger for hours in the air of crowded spaces and rooms such as toilets that lack ventilation, according to a new study by scientists who now recommended wearing masks in public.

While the transmission of the coronavirus from direct human contact and through respiratory droplets, such as coughing or sneezing, is clear, the potential for airborne transmission is much less understood.

The World Health Organisation has said the risk is limited to very specific circumstances, pointing to an analysis of more than 75,000 cases in China in which no transmission from breathing or talking was recorded.

However, a study carried out by scientists from the University of Wuhan and published on Monday in the scientific research journal Nature, suggests the virus can potentially remain in the fair or some time in areas with poor ventilation.

The study took samples from 30 sites across Wuhan, China, where the novel virus was first reported, including inside hospitals as well as public areas of the city during the height of its outbreak in February and March.

It found levels of airborne virus particles in the majority of public areas was too low to be detectable, except in two areas prone to crowding – including the entrance of a department store.

A customer walks past shelves stocked with toilet paper at a grocery store – AP

In open, public areas outside the hospitals such as residential buildings and supermarkets, the study said the concentrations of Covid-19 “aerosols” were generally low.

Meanwhile, in the hospitals, the number of virus particles detected in isolation wards and ventilated patient rooms were very low, but elevated in the patients’ toilet areas, which were not ventilated.

“Airborne SARS-CoV-2 may come from either the patient’s breath or from the virus-laden aerosol from patient’s faeces or urine during use,” the study reported.

People produce two types of droplets when they breathe, cough or talk. Larger ones drop to the ground before they evaporate, causing contamination mostly via the objects on which they settle. Smaller ones – those that make up aerosols – can hang in the air for hours.

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High concentrations also appeared in the un0ventilated rooms where medical staff removed their protective equipment, which may suggest that particles contaminating their gear became airborne again when masks, gloves and gowns were removed.

If the virus is being transmitting in aerosols, it is possible that particles can build up over time in enclosed spaces or be transmitted over greater distances.

The scientists behind the study said it did not seek to establish whether the airborne particles could cause infections.

However, Ke Lan, who led the research, said the work demonstrates that “during breathing or talking, SARS-CoV-2 aerosol transmission might occur and impact people both near and far from the source.” 

As a precaution, the general public should avoid crowds, he wrote, and should also wear masks “to reduce the risk of airborne virus exposure”.

He said their findings highlighted the importance of the ventilation and sterilisation of surfaces, which could be a potential spread source of the virus.

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