Sydney, July 6 : It is time to recognise and mitigate airborne transmission of COVID-19, says a plea to the World Health Organization (WHO) issued by 239 scientists from around the world. The scientists suggest that while measures like washing hands and maintaining social distance are important, they may not be enough to arrest the rapid spread of the disease. The measures that need to be taken to mitigate airborne transmission include providing sufficient and effective ventilation -- supply clean outdoor air, minimise recirculating air -- particularly in public buildings, workplace environments, schools, hospitals, and aged care homes, they said. Supplementing general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal ultraviolet lights can be useful, according to the plea set to be published in the journal Clinical Infectious Diseases. They said that it is important to avoid overcrowding, particularly in public transport and public buildings. Led by air quality and health expert Lidia Morawska, Professor at the Queensland University of Technology in Australia, the appeal is to address the overwhelming research finding that an infected person exhales airborne virus droplets when breathing and talking that can travel further than the current 1.5 metre social distance requirement. "We are concerned that people may think they are fully protected by following the current recommendations, but in fact, additional airborne precautions are needed to further reduce the spread of the virus," Morawska said. The WHO has maintained that Covid-19 infection is primarily transmitted by respiratory droplets expelled by infected people. In its update on June 29, the UN health body said that in the context of Covid-19, airborne transmission may be possible in specific circumstances and settings related to Covid-19 treatment. So the current WHO recommendations emphasise the importance of rational and appropriate use of all personal protective equipment, not only masks, which requires correct and rigorous behaviour from health care workers. Professor Morawska said several retrospective studies of the SARS epidemic had shown that airborne transmission was the most likely mechanism that explained the spatial pattern of infections. "For example, a recent study analysed the data and video records in a restaurant where three separate groups of diners contracted Covid-19, observed no evidence of direct or indirect contact between the three groups, but modelled how the transmission occurred through the air," Morawska said. The 239 signatories from 32 countries come from many different areas of science and engineering, including virology, aerosol physics, flow dynamics, exposure and epidemiology, medicine, and building engineering. "Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are exhaled in microdroplets small enough to remain aloft in the air and pose a risk of exposure beyond one to two metre by an infected person," Morawska said. "At typical indoor air velocities, a 5-micron droplet will travel tens of metres, much greater than the scale of a typical room while settling from a height of 1.5m above the floor." /IANS