Based on guidance from the CDC and WHO, we have been treating COVID-19 like other germs that spread through respiratory droplets (and surfaces contaminated by respiratory droplets). This means we’ve been told to cover our coughs and sneezes, stay at least 6 feet away from others, and wash our hands to prevent viral particles that may have contaminated surfaces from entering our bodies.
But what if this virus can also travel in the air and spread infection just through breathing or talking?
In a recent letter to the White House Office of Science and Technology Policy, infectious disease leaders from the National Academies of Sciences, Engineering, and Medicine recently raised concerns about this scenario. In their letter, they presented evidence of the possibility that COVID-19 could be spread in the air just by breathing or talking.
What’s the difference between droplet, airborne, and aerosol spread?
Respiratory droplets can contain large amounts of virus and are released when an infected person sneezes, coughs, or talks. These droplets are too large and heavy to stay in the air for more than a few seconds and quickly settle out of the air onto surfaces. Because of gravity this is usually within 6 feet, but how far they go can depend on the force of the sneeze or cough.
Airborne infections can spread through air through residue from evaporated droplets or on dust particles. They are much smaller and lighter than droplets so they can stay in the air for long periods of time, in some cases even hours. The key to infections that spread though the airborne route is that they have to be able to survive for long periods outside of the body without drying out and dying off. Infections like measles, chickenpox, and tuberculosis are known to spread through the airborne route, making them highly contagious.
Defining aerosols gets even murkier. It’s somewhere between free-floating airborne viruses and much larger droplets. Aerosols can be described as a tiny virus-filled mist that allows virus to hang in the air and travel further than droplets. Now, there is some evidence that this new coronavirus can spread through aerosols, even when people have no symptoms.
Why does it matter?
If the virus can be released in aerosols when we breathe and speak, and stay airborne, then it changes what we need to do to protect ourselves from becoming infected. We would have to do more than just cover our coughs and sneezes and stay 6 feet apart from people.
It could mean that infectious viral particles could hang in the air for longer periods of time, travel over longer distances, and potentially build up in the air in enclosed places without good ventilation.
It’s especially important for healthcare providers to know so that they can take the proper precautions when they care for patients.
What’s the evidence?
That’s a great question. The evidence is still not conclusive. All we know is that there is enough data to suggest that airborne spread could be a possibility.
Studies that suggest that COVID-19 can become aerosolized include one from the New England Journal of Medicine that got a lot of attention. Researchers looked at how long the virus could survive on various surfaces. As part of their work, they created laboratory conditions in which they showed that the virus could become aerosolized and stay viable (meaning alive, and therefore, infectious) in the air for up to 3 hours. Another study found viral genetic material in areas of COVID-19 infected patients’ rooms on air vents and places where droplets would not have been able to reach. In a study from Wuhan, China, researchers found high concentrations aerosolized particles in rooms where healthcare staff removed their personal protective equipment (PPE), suggesting that particles were able to float through the air after the act of removing PPE, and could potentially also float in the air after cleaning floors or from staff moving around in these enclosed areas.
It’s important to note in the case of these studies, that just because viral genetic material was found in the air in these areas, it doesn’t mean that the virus was still able to infect people. In fact, this is the argument made by the WHO. They point to their own analysis of more than 75,000 COVID-19 cases in China where they did not find evidence supporting airborne transmission.
We need more studies looking for viable virus in air samples when people sneeze, cough, talk, and breathe to get definitive answers. And until then, we won’t know for sure.
How does this change things?
We should probably err on the side of accepting aerosol transmission as a possibility. This should not be cause for panic because spread from these particles likely still depends on how much virus an infected person releases when talking or breathing and also how much time we spend in close proximity to them.
So being in a closed space talking closely to someone who is infected for an hour, is probably more of a concern than standing by someone who’s infected for a few minutes.
For healthcare workers, the possibility of aerosolized transmission means that they really need to be using effective PPE when they are examining patients in small rooms and when they are doing procedures like placing breathing tubes. They should also be careful when they remove their protective gear.
For the rest of us, this adds to the argument that we should be wearing face coverings when we go out in public or when taking care of someone who is sick. It doesn’t hurt to be more aware of our surroundings and to talk to people without getting too close. We should be thoughtful about where and how we remove our face coverings – probably in an open space before we go into our homes. It may also be a good idea to limit time in shared, confined spaces and to increase air ventilation wherever possible.