In the opinion of Donald Milton, this is the ideal situation to spread the coronavirus.
Not only could people transmit the virus directly from one to the other in the small droplets that we all spray to some degree or another when we speak, laugh or sing; but these little droplets also rise in the air where, says Milton, they can float for at least a while.
It's no secret, but agencies seem to be afraid to talk about the aerial nature of the virus, said Milton.
"The airborne word seems to be loaded," Milton, one of the letter's two main authors, told CNN.
"Current guidelines from many international and national organizations focus on hand washing, maintaining social distance and precautions against droplets," wrote Milton and colleagues in the letter published in the journal Clinical Infectious Diseases.
"Most public health organizations, including the World Health Organization, do not recognize airborne transmission, except for aerosol-generating procedures performed in health facilities. Hand washing and social distancing are appropriate, but in our view, insufficient to provide protection against respiratory viruses carrying microdroplets released into the air by infected persons, "they added.
"They don't want to talk about air transmission because it will scare people"
"I imagine we hope that WHO will come and be more willing to recognize the important role of aerosols, whether they want to call it airborne or not," said Milton.
Milton is studying the aerial transmission of viruses. The other main author, Lidia Morawska, is a professor of environmental engineering and an expert in aerosol science at the Queensland University of Technology in Brisbane, Australia. Milton said they and a group of other similar experts have been discussing the potential airborne transmission of the coronavirus since February.
Milton said the group wanted to demystify the word so that health agencies would be less afraid of using it.
"They don't want to talk about airborne transmission because it will scare people," he said. There is also an element of concern that if people think the virus is airborne, they will stop doing other things they need to do to prevent transmission, such as washing their hands, staying away and clean the surfaces.
"The best fear vaccine is knowing and empowering people," said Milton. "I want them to understand how important hand washing is. Why wearing a mask is important because it blocks aerosols at their source, when it is easy to block them." It's more difficult to block aerosols once they float in the air, he said.
The virus is transmitted to droplets that come out of people's mouths and noses, and the size of these droplets varies. Large droplets fall quickly on surfaces and can be picked up on the fingers and transported to the eyes, nose or mouth. Small droplets can stay in the air longer and can be inhaled deeper into the lungs.
"There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or at room scale), and we recommend the use preventative measures to mitigate this airborne pathway. ", wrote Milton and colleagues.
"Studies by signatories and other scientists have shown beyond a reasonable doubt that viruses are released when exhaling, talking and coughing in microdroplets small enough to stay in the air and pose a risk of exposure to distances greater than 1 to 2 meters (yards) from an infected individual, "they added.
"For example, at typical indoor air velocities, a 5 nanometer droplet will travel tens of meters, much larger than the scale of a typical room, while settling from a height of 1, 5 meters (about five feet) on the ground. "
What is not clearly understood is the importance of droplet size for the transmission of coronaviruses, said Milton.
But studies show it's a factor, added Milton. "Many people have huddled together inside where it is poorly ventilated - this is what is causing the pandemic," he said. A noisy bar, where people have to make their voices heard to be heard, is a perfect storm of close contact, poor air circulation and people generating lots of virus-carrying particles by speaking, laughing and shouting.
He said WHO was worried about giving advice that people, especially health workers in resource-poor countries, couldn't follow. The best way to protect workers from fine aerosols is to use an N95 or higher respirator - something that is rare in many places.
Tips to avoid transmission of coronaviruses
But Milton said there are other ways too, including better ventilation, as well as distance and use of the mask. And it's information that the average person, as well as healthcare professionals, can use and act on.
"I am very concerned about the general public and schools and the ventilation in school buildings and dormitories on university campuses and in bars and churches and where people sing and where people gather," he said. he declares.
The group gives practical advice in their letter.
* Provide sufficient and efficient ventilation (provide clean outdoor air, minimize air recirculation), especially in public buildings, work environments, schools, hospitals and retirement homes.
* Supplement general ventilation with airborne infection control devices such as local exhaust, high-efficiency air filtration and germicidal ultraviolet lamps. (These would be placed very high in the ceiling to avoid damaging people's eyes and skin)
* Avoid overcrowding, especially in public transport and public buildings.
"Such measures are practical and can often be easily implemented; many are inexpensive," they wrote.
"For example, simple steps such as opening doors and windows can dramatically increase air flows in many buildings."
In a car, Milton advises, open the windows and make sure the air conditioning or heat is not recirculated but set to include outside air.
In buildings, carbon dioxide monitors can help managers know if the air is properly refreshed, said Milton. Outside in an urban area, he said, carbon dioxide levels are around 350 parts per million in the air. Exhaled breath carries around 38,000 parts per million of carbon dioxide. Indoors, he said, if the air contains 1,000 parts per million or less of carbon dioxide, "that's fine," said Milton.