WASHINGTON • The authorities have come to accept what many researchers have argued for over a year: The coronavirus can spread through the air. That new acceptance, by the World Health Organisation (WHO) and the US Centres for Disease Control and Prevention, comes with concrete implications: Scientists are calling for ventilation systems to be overhauled.

Cleaner indoor air would not just fight the pandemic, it will minimise the risk of catching flu and other respiratory infections that cost the US more than US$50 billion (S$67 billion) a year, researchers said in a study published in the journal Science last Friday.

The study's authors, comprising 39 scientists from 14 countries, are demanding universal recognition that infections can be prevented by improving indoor ventilation systems. They want the WHO to extend its indoor air quality guidelines to cover airborne pathogens, and for building ventilation standards to include higher airflow, filtration and disinfection rates.

The Sars-CoV-2 virus multiplies in the respiratory tract, enabling it to spread in particles of varying sizes from an infected person's nose and throat during breathing, speaking, singing, coughing and sneezing.

The biggest particles, including visible spatters of spittle, fall fast, settling on the ground or nearby surfaces, whereas the tiniest - aerosols invisible to the naked eye - can be carried farther and stay aloft longer, depending on humidity, temperature and airflow.

Although airborne infections such as tuberculosis, measles and chickenpox are harder to trace than pathogens transmitted in tainted food and water, research over the past 16 months supports the role that aerosols play in spreading the pandemic virus.

That has led to official recommendations for public mask-wearing and other strategies. But even those came after lobbying by aerosol scientists for more stringent measures to minimise risk.

Infectious aerosols stay concentrated in the air longer in poorly ventilated, confined indoor spaces, said Professor Lidia Morawska from the School of Earth and Atmospheric Sciences at the Queensland University of Technology.

The role of airborne transmission "has been denied for so long, partly because expert groups that advise government have not included engineers, aerosol scientists, occupational hygienists and multi-disciplinary environmental health experts", professor of global biosecurity Raina MacIntyre, from the University of New South Wales in Sydney, wrote in The Conversation last week.

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