In recent months, there has been controversy over how SARS-CoV-2, the virus that causes, travels from an infected person to others. While formal guidance has often been vague, some aerosol scientists and public health experts have argued that the spread of the virus to aerosols traveling through the air at distances of less than 6 feet is more important than estimated.
In July, 239 scientists from 32 countries pushed the World Health Organization (WHO) to recognize the potential role of airborne transmission in the spread of SARS-CoV-2.
Three days later, WHO did it, declares that under certain conditions, “the transmission of small – scale aerosols cannot be ruled out, especially in certain indoor locations, such as crowded and poorly ventilated areas for a long time with infected people.”
Many scientists rejoiced on social media when the CDC appeared to agree, acknowledging for the first time in a September 18 website update that aerosols play an important role in the spread of the virus. The information stated that COVID-19 can be spread by respiratory droplets or small particles, such as such as those of aerosols produced when an infected person coughs, sneezes, sings, speaks or breathes. These particles can be inhaled into the nose, mouth, airways and lungs and cause infection. It is considered to be the main mode of spread of the virus. ”
However, the controversy erupted again when, three days later, the CDC rejected this guidance, saying it had been posted by mistake, without proper revision.
At this time, the CDC website does not recognize that aerosols typically spread SARS-CoV-2 beyond 6 feet instead of saying“COVID-19 mainly spreads to people who are in close contact (about 6 feet away) for an extended period. It spreads when an infected person coughs, sneezes or talks and drops from the mouth or nose are blown into the air and “Land on the mouths or noses of people nearby. Drops can also be inhaled into the lungs.”
The site says that respiratory droplets can land on various surfaces and people can be infected by concerns these surfaces and then touching their eyes, nose or mouth. “Current data do not support the transmission of SARS-CoV-2 aerosol over long distances, as seen with measles or tuberculosis. Short-range aerosol inhalation is a possibility for COVID-19, as with many respiratory pathogens.” However, this can not be easily distinguished from the transmission of “droplets” according to epidemiological standards.Small transmission is a possibility especially in crowded medical wards and inadequately. “
Confusion surrounds the use of words like “aerosols” and “droplets” because they are not consistently defined. And the word “airborne” has a special meaning for infectious disease experts and public health officials, because of the question of whether the infection can be easily spread by “airborne transmission”. If SARS-CoV-2 spreads easily by airborne transmission, then stricter infection control measures should be adopted, as is the case with airborne diseases such as measles and tuberculosis. However, the CDC told the chief medical correspondent of CBS News, Dr. Jonathan LaPook, that even though airborne spread plays a role with SARS-CoV-2, the role does not seem to be as important as with airborne infections such as measles and tuberculosis.
All of this may sound like a violent science debate that is deep in the weeds – and it is – but it has far-reaching implications as people try to figure out how to stay safe during a pandemic. Some tips are intuitively obvious: wear a mask, wash your hands, avoid crowds, keep your distance from others, the outside is safer than the inside. But what about this “6 foot” rule for maintaining social distance? If the virus can travel indoors for distances longer than 6 feet, does it make sense to wear a mask indoors whenever you are with people who do not belong to your “pod” or “bubble”?
Understanding the basic science behind how SARS-CoV-2 travels in the air should give us strategies to stay safe. Unfortunately, there are still many open questions. For example, even if aerosols produced by an infected person can float in a room and even if aerosols contain a viable virus, how do we know how important the possible mode of transmission in a pandemic is?
As we await answers from current research, Dr. LaPook turned to three top scientists to try to clear the air. Recognizing that science has not yet been set in stone, they generously agreed to give us the best advice on how to think about our protection, based on their current understanding of how SARS-CoV-2 can spread . Below, atmospheric chemist Kimberly Prather, airborne virus expert Linsey Marr, and environmental health professor Donald Milton discuss the best precautions you can take to reduce your risk of infection.
Contrary to popular belief about the importance of transmission through contact with large respiratory droplets, it turns out that an important way in which humans become infected is by breathing in the virus. This is more common when someone is 6 meters away from a person who has COVID-19 (with or without symptoms), but it can also happen more than 6 meters away.
Viruses in small, airborne particles called aerosols can infect humans both near and far. Aerosols can be considered as cigarette smoke. While they are more concentrated near someone who has the infection, they can travel more than 6 feet, delay, accumulate in the air and remain contagious for hours. Therefore, to reduce the chance of this virus being inhaled, it is vital that you take all of the following steps:
Practice physical distance – the farther away the better.
Wear a face mask when you are with others, even when you can maintain physical distance. Face masks not only reduce the amount of virus coming from people who have the infection, but also reduce the chance of inhaling the virus.
Improve ventilation by opening windows. Learn how to clean the air effectively with methods such as filtration.
Wear a face mask if you can not physically move at least 6 feet or, ideally, more.
Whenever possible you should have all four of these components in place for launch to maximize profits.
Whether you are internal or external, remember that the risk increases with the duration of your exposure to others.
With the issue of broadcasting, it is not just the audience that is confused. There was also confusion among scientists, doctors and public health officials, in part because they often used the words “droplets” and “aerosols” differently. To address the confusion, participants in a workshop in August on the airborne transmission of SARS-CoV-2 at the National Academies of Science, Engineering and Medicine unanimously agreed on these definitions for air droplets and aerosols:
Droplets are larger than 100 microns and fall to the ground within 6 feet, traveling like tiny balls.
Aerosols are less than 100 microns, are very close to one person, can travel more than 6 feet and can be delayed and accumulate in the air, especially in rooms with insufficient ventilation.
All respiratory activities, including breathing, speech, and song, produce far more aerosols than droplets. A person is much more likely to inhale aerosols than to spray with a drop, even at a short distance. The exact rate of aerosol droplet transmission has not yet been determined. We know, however, from epidemiological and other data, especially from the over-dissemination of facts, that the infection occurs through the inhalation of aerosols.
In short, how do we get infected with SARS-CoV-2? The answer is: In the air. Once we recognize this, we can use the tools we already have to help end this pandemic.
Kimberly A. Prather, PhD, Distinguished Chair in Atmospheric Chemistry, Scripps Institution of Oceanography, UC San Diego.
Linsey C Marr, PhD, Charles P. Lunsford Professor of Civil and Environmental Engineering, Virginia Tech.
Donald K Milton, MD, DrPH, Professor of Environmental Health at the University of Maryland School of Public Health.