How Coronavirus Spreads and How to Prevent Coronavirus : It’s becoming clearer and clearer now, that this coronavirus spreads not just through contact and respiratory droplets that fly through the air like ballistics, but also it’s being transmitted through the airborne route, meaning through aerosol, meaning the virus lingers in the air, and then someone inhales the virus. This is known as airborne transmission.
Let’s face it, there is a reason why hospitals with designated COVID-19 areas require everyone to wear an N95 respirator mask, as well as eye goggles. That’s because we know that this virus has the potential for airborne transmission. During normal breathing and speech, tiny particles are emitted mainly from the mouth. These particles can range in size, with the smallest being less than a micron (1 um), and the biggest being over 500 um in diameter.
To put some perspective on that, the average diameter of human hair is about 80 microns). Typically droplets that are less than 5 um are considered small, and its these small droplets that can be suspended in the air. Droplets that are over 100 um are considered large, and in between 5 and 100 microns is intermediate. But the reality is, it’s a range of sizes, it’s a continuum, from less than 1 um to over 500 um. And more and more particles are emitted when someone is breathing heavier, such as with exercise, or if someone is coughing or sneezing, or if someone is shouting or singing.
Due to gravitational forces, particles that are bigger than 5 microns tend to settle, meaning fall down on surfaces such as the floor, and they fall fairly close to the source, typically within 6 feet. This is why the CDC recommends 6 feet for social distancing. But here’s the thing, sometimes these larger particles travel further than that, especially if someone is breathing heavy, or shouting, or singing, or coughing, or sneezing.
Typically they fly no further than 12 feet in these situations. But we’re also spraying particles that are smaller than 5 microns, and its these tiny particles that don’t act like ballistics, they act more like a gas cloud, where they float in the air, and travel up to 27 feet. The ones that are less than 1 um evaporate within milliseconds of hitting the air, while the particles that are more than 100 um can take up to a minute to evaporate.
What happens when the droplets that are less than 5 microns, what if they are spewed from someone who is infected with the virus, and all of a sudden in midair, they evaporate? Well, they dry out, and you’re left with a virus that is floating in the air. These are called droplet nuclei, aka aerosols.
There are lots of factors that determine how long aerosols remain in the air. It depends on the person who emitted the particles, how they emitted them, the temperature, and humidity of the environment. Lack of airflow means this cloud will persist longer. And when this moist cloud finally does dissipate, you’re still going to have droplet nuclei that stay airborne for about 3 hours, based on that NIH study.
At this point, we might not have 100% conclusive evidence that proves airborne transmission, but there are now several studies that strongly suggest that to be the case. Now just because we know that this virus spreads through the airborne route, that’s not to say that it doesn’t spread through contact and respiratory droplets, meaning the bigger droplets that act like ballistics. It spreads by all 3 of these mechanisms.
So hand washing is still important. As is not touching your face or mask with dirty hands. And maintaining 6 feet apart is a good thing, but its not good enough for certain situations. Remember earlier how I said when someone sneezes, that moist cloud containing aerosols can travel up to 27 feet?, And the virus can linger in the air for 3 hours.
Some rooms have adequate ventilation that supplies clean outdoor air and minimizes recirculated air. The better the ventilation, the less likely the spread of aerosols. And even cracking open a window can make a huge difference, and having a fan blowing is good too. Other measures can help too, like having an air purifier with high-efficiency air filtration, and germicidal UV lights.
Here are my recommended items:
Regular Medical/Surgical Mask
Elastomeric Respirator Mask to Prevent Inhaling The Virus
Glasses/Goggles to Protect Your Eyes
Pulse Oximeter to measure your Oxygen at Home
Dr. Mike Hansen, MD
Internal Medicine | Pulmonary Disease | Critical Care Medicine
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