The deadly coronavirus may be spread through mere breathing or speaking and not just coughing and sneezing.

This is the new scientific view of the U.S. National Academy of Sciences (NAS).

In a letter sent to the White House on April 1, the academy said that though research isn’t yet conclusive, “the results of available studies are consistent with aerosolization of virus from normal breathing.”

Dr Anthony Fauci, head of infectious diseases at the U.S. National Institutes of Health, cited the report when he spoke with Fox News on Thursday.

He used it to recommend that Americans should wear the face mask when outdoor.

Until now, US health agencies had said the primary pathway of transmission is respiratory droplets, about one millimetre in diameter.

The droplets are expelled by sick people when they sneeze or cough.

These quickly fall to the ground around a meter (three feet) away.

But if the virus can be suspended in the ultrafine mist people expel when exhaling — in other words, an aerosol — it becomes much harder to prevent its spread.

A recent NIH-funded study published in the New England Journal of Medicine found that the SARS-CoV-2 virus could become an aerosol and remain airborne for up to three hours.

The paper received widespread attention even as critics said the findings were overblown because researchers had used a medical device called a nebulizer to deliberately create a viral mist, something they argued would not occur naturally.

The NAS letter pointed to preliminary research by the University of Nebraska Medical Center that found the genetic code of the SARS-CoV-2 virus, its RNA, in hard-to-reach areas of patients’ isolation rooms.

The NAS scientists also cited two other studies — both not yet peer reviewed — from Hong Kong and mainland China.

The Hong Kong researchers had some patients with coronavirus and other viral respiratory illnesses wear masks, while other patients in the study didn’t cover their faces.

They found fewer droplets and aerosols from coronavirus patients who wore masks.

The Chinese paper raised concerns that personal protective gear used by health workers could be a source of airborne virus.

The team studied hospitals in Wuhan and found two major areas where the virus was aerosolized: patient bathrooms and rooms where medical staff removed protective gear.

This may be because doffing protective gear causes particles to get re-suspended in the air. Even if these particles are not of breathable size, they could settle on people’s hands and bodies, the NAS panel said.

So far, the World Health Organisation has been more cautious on the airborne threat.

In an analysis published on March 29, it wrote that aerosol transmission was only known to occur during particular medical treatments that required assisted breathing.