Facemasks, Particle Size, and Your Chances of Catching COVID-19

One thing that becomes obvious in a pandemic is how much we don’t know for sure. 

It took thousands of cases of this new coronavirus to show that the disease is more lethal for men. It took weeks to discover that ex-smokers were as vulnerable as current smokers. It took tens of thousands of cases to show that being young did not protect you.

And now, we wrestle with the facemask problem.

Doctors are divided on this issue with good reason. Even with more than 1 million known cases around the world, we do not yet know exactly how this disease spreads.

At first, it seemed to pass only through direct contact with droplets in the air. It took a turbulent exhalation—a sneeze, cough, or snort. Smaller particles, called bioaerosols, from regular breathing did not seem to be a problem.

If aerosols don’t matter, then we don’t need to wear facemasks as long as we keep our distance.

That is why, for several weeks, agencies like WHO and CDC recommended social distancing of 6 feet to slow the spread of COVID-19.

Then came a few dissenting voices and a choir.

On March 10, members of the Skagit Valley Choral in Washington State met for rehearsal. Leaders told choir members to stay home if they felt sick or had any symptoms. They did. Only 60 seemingly healthy people showed up for practice, about half the usual choir. They spread out to be as far as possible from one another to practice. No one coughed or sneezed. Most of them avoided touching anyone.  And yet, within three weeks, two choir members died of COVID-19, another was hospitalized, and 45 more became ill with the disease. 

We still do not have the final word on facemasks or how COVID-19 spreads. Meanwhile, we do have a few facts to consider that may help you with your personal decision.

The most important is that this “flu” is not the regular flu because it is 100 to 200 times more likely to kill anyone who gets it. In Wuhan province, where it first occurred, it was 230 times more lethal than flu. In Italy, where the population is older than most countries, it has been 900 times more likely to kill. In other places, the rate is lower. But not as low as the flu anywhere where at least a few hundred cases have occurred.

That is why you do not want to catch it.

Now consider the particle size question. A droplet, such as found in a sneeze, measures 5 to 10 micrometers (microns).

A particle that size can only travel a short distance before falling to the ground. It is unlikely to land on your face and get into your eyes, nose, or mouth unless someone sneezes close to you.

Aerosols are particles that are smaller than 5 microns. They can travel long distances, wafting in the air.  And they can stay aloft anywhere from a few minutes to an hour or more.

For your consideration, here are a few particle sizes from some pollutants you are likely to encounter, from the smallest to the largest:

Smoke from natural materials 0.01 to 0.1 micron

Cornstarch dust 0.1 to 0.8

Tobacco smoke 0.02 to 25 microns

Talcum dust 0.05 to 50 microns

Burning wood 0.2 to 3 microns

Outdoor dust 0.5 microns

Fog 1 to 40 microns

COVID-19 DROPLETS IN SNEEZES 5- 10 MICRONS

Pollen 10 to 1000 microns

Human hair is 60-120 microns

Dr. Lisa Brosseau at the Center for Infections Disease Research and Policy at the University of Minnesota is well aware that particles of 5 microns or smaller—like wood smoke—can remain in the air for several minutes or even hours.  

This is why she suspects that droplet transmission of COVID-19 may be a less important source of infection than many people assume… because someone sneezing or coughing so that droplets land directly in our mouth, eyes, or nose are rare.

But we can breathe in aerosols from a sneeze whether we are near the source or many feet away.   Thus, the six-foot rule does not protect us if aerosols can transmit COVID-19.

That’s a maybe at the moment. It’s not clearly the case because scientists have not been able to prove it beyond doubt yet. Even if tests can measure the RNA from COVID-19 droplets in the air far from the source or detect them on a surface hours later, no one knows whether those particles are still active disease vectors.

But there are substantial reasons to suspect aerosols matter—like the choir practice that turned deadly or cases where people who could not remember anyone sneezing or coughing near them became ill.

Another thing that may help you decide what to do about your personal decision on a facemask is this: you breathe aerosols more deeply into your lungs than droplets.

At this point, you have a choice based on the best evidence at the moment, which is subject to change in the weeks ahead. But if you can smell cigarette smoke or wood fire, then you have an idea of how hard it would be to avoid breathing in aerosols the size of COVID-19. Outdoors, you might not get a large enough “dose” of COVID-19 particles as they spread out naturally. But in an enclosed room, concentrations tend to rise.

Stay distant for sure. Consider a facemask if you are likely to encounter a concentration of COVID-19 particles. Just in case. Especially if you have health issues like asthma, COPD, diabetes, obesity or you are a smoker.

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