Updated: Dec 28, 2021
There is some misinformation going around about the transmissibility of SARS-COV2 in the air.
I was sent this article by a friend “Steer clear of people when exercising outdoors during a coronavirus pandemic” published in the Boston Herald. https://www.bostonherald.com/2020/03/27/coronavirus-how-to-stay-safe-exercising-outdoors-during-the-pandemic/
In the article, it is recommended that people should remain at least 25 ft away from each other when exercising outdoors. The author based the recommendation on an analogy of airborne smoke particles. While the recommendation was based on aerosol science, it does not take into account the biology (or physics) of respiratory droplets.
All the current scientific evidence suggests that, outside of healthcare settings, this virus is NOT airborne.
This coronavirus is a respiratory virus. It hangs out in the epithelial cells in your nose, throat, and lungs. After infection, you enter the latent period, the virus has entered your body and it’s using your own cells to replicate, but you are not yet shedding the virus. With this virus, as early as 24 hours after exposure you become infectious, meaning the virus is being released from your cells into airway spaces. This is the subclinical infectious period (pre-symptomatic period), it is during this period and the subsequent infectious period where you can infect others.
When you are infectious, the virus is modifying your behavior. It is wanting to make you cough or sneeze. The more efficient it is at making you do this, the better chance the virus has of finding a new host. Those large droplets released from a cough or sneeze are packed with infectious material, just hoping to find a mouth, nose, or eyes to land on…… We all know that we should stay away from someone with symptoms… or better yet stay home if you have symptoms!
But the more subtle risk comes from an infectious person and their breathing. During the process of breathing, you expel respiratory droplets. Tiny little droplet of water/mucus which can contain the virus. But these droplets have weight and are subject to gravity. Most respiratory droplets fall into the 100um to 50um size range. The larger 100um droplets hit the ground within 3 feet, while the smaller droplets drop within 6 feet. Droplets that are smaller (also known as infectious droplet nuclei) can travel great distances but the virus needs to be really tough to survive in those small droplets. As an example, measles can survive in small droplets and travel at least 18 meters (54ft) in the air.
Outside of healthcare settings, all the evidence suggests that SARS-CoV2 is only found in respiratory droplets, and therefore, will fall out of the air within a distance of 6 ft from the infected person. This is how the personal distancing distance guidelines were established.
Health Care Settings: Why are healthcare setting different. Because some procedures used in healthcare settings, such as intubation or suctioning, create high-velocity aerosols. Even the hospital toilets, without lids, create aerosol particles. These aerosols can remain in the air for many minutes and travel greater distances. Once aerosolized, the SARS-CoV2 virus takes about 3 hrs to become non-viable.
Therefore, in health care settings, workers bring themselves in close contact to more people with more severe symptoms in relatively enclosed spaces, and are at more risk than the general public at being exposed to a dose of infectious particles that could lead to infection. This can come from respiratory droplets or aerosols. Higher doses of infectious particles are more likely to result in infection and disease.
Normal situation: 6ft/2 meters is the distance at which the overwhelming majority of infected respiratory droplets fall out of the air. They hit the ground within 4 seconds. So, when we talk about physical distancing, stay 6 feet apart and those droplets won’t reach you. Guard that distance when you are shopping or speaking to someone!
Exercising: Respiratory droplets may travel slightly further when exercising, as they are being exhaled at a higher velocity, but they still hit the ground very quickly: again, within 4 seconds and travelling only about 1 ft further. There is no need to be running 25 ft away from each other, or run to the other side of the road when a fellow exerciser is coming by.
It’s just not supported by the data.