This is part three of our summary from our recent review of a Grand Rounds presentation provided by UCSF titled: “How the virus gets in, and how to block it: Aerosols, Droplets, Masks, Face Shields and more.”
To be clear SARS-CoV-2 is the name of the virus that causes CoVID-19. For simplicity, I will use these two names interchangeably for the duration of this summary. This, of course, does not constitute medical advice nor does it create a doctor-patient relationship between you (the reader) and me.
Key Takeaway: Face shields are an additional layer of protection for the wearer and are essential for eye protection. At the completion of this lecture, I bought face shields for my family to wear in addition to masks (except for my youngest who pulls down his mask to suck on his thumb, as many of you know from our Zoom demos . He will probably wear the face shield alone).
Michael Edmond, MD, MPH, MPA Chief Quality Officer and Associate Chief Medical Officer, University of Iowa Health Care; Professor of Medicine, Division of Infectious Diseases, University of Iowa Carver College of Medicine
Data on COVID epidemiology shows the attack rate of SARS-CoV-2 (i.e the percentage of people ill) is overall 5%, passing interactions while shopping 0.5%, sharing a meal 7%, household contacts 10-40%. As a business owner it stands out to me that sharing a meal causes such a large increase in infections. This might lead me to consider specific regulations related to distancing in meal breaks and sharing of food or business lunches.
That brings us to the final section of the grand rounds, face shields. Remember above when we talked about where we have receptors for the SARS-CoV-2 the virus that causes COVID-19. The eyes may have stood out. Masks do nothing to protect your eyes from particles in the air. Face shields can provide protection to your eyes, can also provide protection for your mask and decrease your exposure to infectious particles.
There are no national standards on face shields, but the optimal face shield design is one that extends below the chin and nearly to the ear on both sides, and has no gap at forehead (or gap covered) so that particles cannot fall down onto your face/eyes from above.
Face shields have some advantages over masks. They are more comfortable, not as hot, less claustrophobic, have no impact on breathing, are easy to disinfect, protect against touching face, and are helpful for hearing impaired who rely on reading lips. The disadvantages are mainly glare, they are bulky and optically imperfect.
The best study of face shield effectiveness involved flu prevention. In that study face shields reduced aerosolized viral particles of 8.5 microns or greater by 96% at 18 inches from the source and 68% for smaller aerosolized particles. Said differently 4% of the larger particulate and 32% of the smaller particles got past the shield. Again, as we mention in our prior post - N95 masks filter out 90-95% of viral particles, and surgical and cloth masks filter 65-85%.
Utilizing universal masking AND face shields along with effective pre-work employee health screening protocols may significantly reduce the risk of an outbreak spreading in your organization. And, if people were to become infected, it is likely that their viral “dose” would be lower, hopefully leading to less severe infections allowing more of your employees to return to you.