In early July, a group of scientists authored an article outlining the evidence for COVID-19 being an airborne disease. It made plenty of headlines, which was, frankly, a bit confusing. Didn’t the public already know that COVID-19 was a respiratory illness? And didn’t medical providers already know that COVID-19 could be transmitted by aerosols in some situations, not just droplets? Why was this news, exactly?
To understand the confusion, we have to go back to the definition of airborne. In medical parlance, an “airborne” disease is one that is spread primarily by the distribution of aerosols—tiny particles, less than 5 microns in size, that can linger in the air and travel long distances. They can also travel lower into your respiratory tract. Classic examples are chicken pox, measles, and tuberculosis. In contrast, a “droplet disease” is one that is primarily transmitted by much larger droplets (20 microns or larger) that don’t linger in the air and don’t travel long distances—they typically fall to the ground within about 3 feet of the source. Classic examples are influenza, mumps, and whooping cough. These droplets can land in your eyes, nose, or mouth, and infect you, or be transferred from fomites (surrounding objects) to hands, and thereby to the face, infecting the respiratory tract by direct contact with mucus membranes in the eyes, nose, or mouth. But that doesn’t mean you can think of a droplet disease as requiring direct contact—this kind of disease can infect you either when you inhale it or when you have direct contact with it.