CDC MASKS UPDATE: Click Here
Presented by Dr. MZ This column, which will appear weekly, is intended to help all of us do our part in combating this virus and saving lives.
Everywhere you go in public nowadays people are wearing masks. If you aren’t wearing one, you begin to feel like a renegade, an outlier, like someone who just doesn’t get with the program. But is there any validity to that sensation? Should I be wearing a mask?
Let’s review what science tells us about this question:
SARS CoV-2 is a tiny particle, about 0.125 microns in diameter, varying in size from 0.06 to 0.14 microns. Mask barriers have been tested in the laboratory by putting particles of differing sizes, using a diesel generator, through different masks. In these tests, particles as small as 0.07 microns in diameter are detected by a particle counter on the opposite side of the mask. Here are the results of these experiments:
- A cotton handkerchief blocked 28% of particles down to 0.007 microns
- A surgical mask blocked 80% of particles down to 0.007 microns
- Various N95 masks blocked 95% of particles down to 0.007 microns.
The conclusion: surgical and N95 masks can capture particles that are up to 10 times smaller than SARS CoV-2 and therefore have varying utility in protecting against the inhalation of SARS CoV-2. The cotton handkerchief did not do well.
N95 masks are firm, multi-layered, and cup-shaped. They come in different sizes and must be fit tested to the wearer’s face in order to promote a tight seal around the edges. Facial hair makes a tight seal impossible. N95 masks must be donned (put on) and removed properly to avoid contamination. While effective, they are hot and uncomfortable over long periods of time. They also increase the work of breathing because the wearer has to pull air through them, which means the wearer feels just a bit short of breath while wearing them.
So how do these masks do when they are on someone’s face? Because of the fit testing and the tight seal, N95 masks capture 95% of 0.01 micron particles when worn on the face but surgical masks, because they fit much more loosely, only capture 63% of 0.01 micron particles. You can imagine that the cotton handkerchief wouldn’t do well on a face at all.
Surgical masks are made from non-woven fabric that has better bacteria filtration (bacteria are much larger than viruses) and air breathability than woven cloth. They are not designed to filter viruses. The mask material is usually polypropylene. Surgical masks are multilayered, generally by covering a layer of textile with non-woven bonded fabric on both sides.
N95 respirators (masks) consist of multiple dense layers including a high-efficiency melt blown, electret, non-woven material which determines filtration efficiency. Some N95 masks have a one-way exhalation valve in the center to make breathing easier.
The Centers for Disease Control and Prevention (CDC) guidance calls for the use of N95 respirators or more powerful respirators (power-assisted particle respirators, otherwise known as PAPRS) when a pathogen is transmitted by the airborne route. The airborne route means that the pathogen particles are usually tiny and hang in the air for a period of time measured in hours as opposed to larger droplets which fall to the ground almost immediately. Classical airborne pathogens are the measles virus (producing the mother of all contagious diseases), the chickenpox and smallpox viruses, and the tuberculosis bacterium. Whether or not SARS CoV-2 is significantly transmitted by the airborne route is still not definitively determined. It is known to hang in the air for 3 hours in the laboratory setting.* Optimal protection of a healthcare provider (HCP) from SARS CoV-2 includes the use of an N95 mask. As supplies of N95 masks have been limited, surgical masks with face shields are being used with the acknowledgment that this solution is less than optimal.
The use of a cloth mask, consisting, perhaps, of a tightly woven fabric and an inner layer of cotton flannel, or the use of a bandana or scarf is not adequate respiratory protection for HCPs with ongoing exposure to COVID-19. Conceivably such a mask might be marginally better than a bare face but there are no real-world data to prove this concept. The only possible benefit from the homemade mask might be as a barrier to touching one’s face. Under “Options for when no facemasks are available”, the CDC does list HCP use of homemade masks (e.g. bandana, scarf) with a face shield for the care of patients with COVID-19 “as a last resort “(Italics mine). The next sentence in the guidance says, “However, homemade masks are not considered PPE (personal protective equipment) since their capability to protect HCP is unknown.”**
Surgical masks and possibly homemade masks are sometimes used for what is called “source control.” This means that the mask is put on the patient, the person who is thought to be infected and is coughing. The concept is that the mask serves as a barrier catching the large respiratory droplets that are emitted by the patient wearing the mask. This means that the mask is lending protection to the people who are NOT wearing masks, not to the person who is wearing the mask.
So back to the initial question, should I be feeling guilty because I am not wearing a mask? People who wear surgical or cloth masks in public are not protecting themselves. SAR CoV-2 can enter their upper respiratory tract when they inhale through the mask and around the top, sides, and bottom of the mask. People who wear masks in public are possibly protecting others from any large respiratory droplets that they might expel. Remember, however, that large respiratory droplets fall to the ground almost immediately so in a public setting they aren’t much of a threat. People ill enough to wear a mask or people ill with COVID-19 should not be out in public at all. Healthy people do not need to wear masks. They derive no protection for themselves from doing so. Healthy people who wear surgical masks in public are, however, using up mask supplies that are desperately needed by HCPs.
I will also not be sewing homemade masks, not because I don’t care (on the contrary, I care for my fellow HCPs profoundly) but because I know homemade masks are not sufficiently effective in protecting HCPs. I recognize that people want to help but the right answer is to get the proper and scientifically proven effective PPE for our HCPs. Whatever it takes to get proper PPE to them should be done. Our healthcare providers are our most valuable asset in dealing with this pandemic. We must do everything in our power to protect them and to protect them effectively.
Feel free to send questions and concerns about COVID-19 and this pandemic to healthcare [at] LWV-PA.org. They will be collated and addressed in future columns; individual answers to individual questioners will not be provided. Please stay safe, sneeze or cough into a tissue (disposed of properly), don’t forget to wash your hands, stay 6 feet away from others, and, as much as humanly possible, don’t touch your face.
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Dr. Margan Zajdowicz is the Co-Chair of the League of Women Voters-Pasadena Area Healthcare Committee and a retired infectious disease physician who spent many years in clinical practice and emergency preparedness and pandemic planning for the US Navy. She holds a Doctor of Medicine degree from the University of Maryland School Of Medicine and a Master of Public Health degree from Old Dominion University/Eastern Virginia School of Medicine.
*https://www.nejm.org/doi/full/10.1056/NEJMc2004973?query=featured_home
** https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/face-masks.html
