The World Health Organization said Tuesday it has been looking into the possibility that the novel coronavirus can be transmitted by air, after international scientists urged the WHO to revise its guidelines for the virus.

A WHO official said at a press conference that the risk of airborne transmission cannot be totally ruled out, especially in crowded, closed or poorly ventilated indoor settings, adding the organization will continue to explore all potential infection routes.

Photo taken on Feb. 14, 2020, shows the headquarters of the World Health Organization in Geneva. (Kyodo) 

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The Geneva-based health agency has said the novel coronavirus is transmitted via droplets emitted when people cough or sneeze that can be scattered to up to 2 meters but then fall to the ground. Therefore, it has been advising people to remain more than 1 meter apart and sanitize their hands.

The droplets measure 5 microns, or 0.005 millimeter, in diameter. The international scientists suggested the virus could be transmitted through smaller particles suspended in the air, in the same way as tuberculosis and measles.

The New York Times reported Saturday that more than 200 experts from 32 countries had sent an open letter to the WHO urging it to revise its guidance for the novel coronavirus. They pointed to the risk of infection not only through large droplets but also smaller particles lingering in stagnant air.

The newspaper said the experts had been warning for months that tiny particles, or aerosols, can be emitted when an infected person simply breathes or talks and they can remain in the air for hours, especially in places with poor ventilation.

On Tuesday, the WHO official advised against entering crowded and closed settings with poor ventilation and recommenced wearing face masks where adequate social distancing cannot be maintained.

Tuberculosis bacteria and the measles virus spread through the air and are both highly infectious, with around a quarter of the world's population believed to be infected with the former.