Airborne virus may mean facemasks in offices and windows open even in winter

SHOULD more of us wear face masks in the office and will classroom windows have to remain open in winter? The possibility of airborne transmission of Covid-19 – especially in “crowded, closed, poorly ventilated settings” – cannot be ruled out, according to the World Health Organisation (WHO).

It has responded to a letter signed by 239 scientists in 32 countries – including Ireland – asking for more clarity and calling for this mode of transmission to be considered.

How does this differ from what we already know and what precautions are needed to reduce the risk of catching the virus in this way?

Sinking droplets

The WHO has previously said that Covid-19 primarily spreads in small droplets expelled from the nose and mouth of an infected person through, for instance, coughs and sneezes. These droplets quickly sink to the ground.

Because these droplets are large they fall within a metre or so – hence the advice on physical distancing. The droplets can land on surfaces and if these are touched by someone the virus may be picked up.

Lingering particles

The difference between the droplets and airborne disease is that tiny particles from a sneeze, cough or breath can linger in the air.

These aerosols can travel further than a metre. It means the infectious person moves on but the virus remains airborne. Another person can breathe it in.

Jury is out

It is still not clear-cut if airborne transmission is possible and, if so, what is the extent of the role it plays in the spread. The WHO is to publish a scientific brief summarising the state of knowledge on modes of transmission of the virus in the coming days.

Benedetta Allegranzi, the WHO’s technical lead for infection prevention and control, said there was evidence emerging of airborne transmission of the coronavirus, but that it was not definitive.

”The possibility of airborne transmission in public settings

– especially in very specific conditions, crowded, closed, poorly ventilated settings – cannot be ruled out. However, the evidence needs to be gathered and interpreted, and we continue to support this.”

Reducing risk

There are so many aspects about the virus that started out being suspected and then proven to be correct. So even if there is no strong proof of airborne transmission, there are likely to be recommendations by some countries to tighten up safety precautions.

It could lead to wider use of face masks or coverings in offices or even classrooms.

The occupancy levels of some rooms may be looked at and also the length of time people spend indoors in confined workplaces, bars or restaurants with others unless wearing a mask. There may be stricter guidance on singing and shouting in indoor areas.

Better ventilation

A key measure to reduce the risk of airborne transmission is likely to include ensuring there is better ventilation where people are gathered in a room. Windows and doors could end up having to be opened in schools, colleges and workplaces, even in colder weather. Filtered air conditioning systems will be needed. Researchers at the University of Hong Kong highlighted the case of nine people in three families in China who caught the virus after eating at the same restaurant as a “source” patient. They said coughing and sneezing alone could not explain the spread. The conclusion pointed to aerosol transmission.

Healthcare settings

There could be potential consequences for healthcare settings and the grade of face mask that staff wear. It could mean they will have to don the most secure masks which filter out even the smallest respiratory droplets as they care for patients and look after residents in nursing homes and residential centres.

This could lead to problems with supplies of these masks.

Absence of evidence

The scientists who wrote the letter to WHO say an absence of evidence around airborne transmission is not evidence of absence.

They insist the potential for this kind of transmission is important as countries increasingly move out of lockdown and people mix more for longer in workplaces, pubs and other enclosed spaces.