Covid-19: How the Virus Gets in and How to Block It: Aerosols, Droplets, Masks, Face Shields, & More

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In this Covid-19 Medical Grand Rounds (July 16, 2020), three world experts discuss a variety of issues surrounding how the coronavirus moves from person to person, how best to block viral spread, and the potential that mask-wearing may not only prevent infection but also lead to a milder clinical course. The questions regarding aerosol vs. droplet transmission and the value of wearing masks and/or face shields are central to formulating public health strategies as well as to informing the personal decisions that each of us makes every day. The session is hosted by UCSF Department of Medicine chair Bob Wachter.

Bob Wachter: Introduction
00:04:45 – Aerosol vs. Droplets:
Don Milton, Professor, Environmental & Occupational Health, University of Maryland School of Public Health
00:25:35 – Q&A
00:29:03 – Masks:
Monica Gandhi, UCSF Professor of Medicine; Associate Chief of Division of HIV, Infectious Diseases, and Global Medicine at ZSFG; Director of the UCSF Center for AIDS Research; and Medical Director of the HIV Clinic, Ward 86, ZSFG
00:45:46 – Q&A
00:48:25 – Face Shields:
Michael Edmond, 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
01:06:14 – Q&A
01:08:10 – Panel Discussion
01:28:57 – Bob Wachter: Closing

See previous Covid-19 Medical Grand Rounds:
• July 9: The State of the Pandemic, Opening the Schools, and the Outbreak at San Quentin State Prison
• June 25: Special Presentation: An Interview with John Barry, Author of the Bestselling Book, The Great Influenza: The Story of the Deadliest Pandemic in History
• June 18: Covid-19: Update in Therapies (including Steroids), and Covid Patients with Persistent Symptoms: What’s Going On?
• June 11: Covid-19: Update in Epidemiology, and, Are the Publication and FDA Approval Processes Moving Too Fast for Safety?

💬 Comments on the video

The best teachers can dumb it down just enough so that dummies like me can grasp the broader concepts. 1 of the 3 presenters did not succeed at this (big thanks to the other 2!). Also, PowerPoint tip: less words.

Author — erp65


people who know they are not feeling well still go out and mingle amongst others. I think this is actually the greatest mode of transmission.

Author — bamnibaum


We have been here in Thailand since this began. I find it interesting that so many people refuse to look at the measures in place where entire populations have stopped infection spread. Over 64 days with no transmission.

Author — Jack Fletcher


I am an atmospheric scientist. In our field any particles suspended in the atmosphere is by definition an aerosol. I would like to suggest that medical professionals use the term "small aerosols" in place of what you called aerosols, to be consistent with atmospheric sciences.

Author — C Chang


This has been a tremendously interesting and encouraged by this channel. I found this broadcast particularity interesting and informative.
In my commercial life I worked to help protect industrial vehicle operators from respirable silica. I understand and sympathize with those confused by the imprecise language often surrounding the exact definitions in that field. There needs to be a meeting of the minds between doctors, scientists, and engineers on the terms we will use to describe things in our air.

Naturally this virus has captured my imagination. I have been building portable HEPA and electrostatic filtration units for use in the event that one of us becomes infected and needs care at home. Being in a high risk group myself I am greatly encouraged to learn that my efforts may not be in vain, that reducing exposure may well reduce the impact of any second infection in our house.

But I hesitate to put masks on our two cats. They are not without the ability to resist forcefully. I think they are Republicans but they won't say. Only our dogs will show me their voter registration cards.

Author — Bill Kerr


With small viral aerosols, the eyes are also exposed. So if masks actually stems the spread of COVID-19, then we should also wear goggles. Shouldn't we?

Author — Ettenyl56


Thanks Bob & team at UCSF. I know it takes a lot of work pulling these together and it is really appreciated.

Author — Don't Worry Be Happy


It is so important to understand that death isn't the only concern from infection. Alive, but with badly scarred lungs, badly damaged blood vessels, or badly damaged liver or kidneys isn't a great outcome. All three? The quality of your life will be poor for the REST of your life.

Author — Cathy


"The public" is not just walking around in open spaces. Sometimes have to work indoors with many others that dont wear face covers, mask or they wear it wrong.
For us in construction, wearing elastomer P100 respirators or full face respirators with fabric on top of the exhaust valves is the best way of been safe in a setting where we cant keep distance from each other, ventilated spaces and we have to spend 8 hrs indoors with people huffing and puffing.
So, the "public" also have to work and sometimes at as much risk as you healthcare providers, but with a fraction of the wages and bad health coverage. We are more vulnerable so we also need to wear better PPE.

Author — Carlos PenaGarrido


For the general population of USA to adopt, you can't have Walmarts selling 15 allergy masks for $29.99 when November 2019 they were selling 30 allergy masks for $5.47. People in my area will not spend $30.00 USA dollars on 15 masks, when they've lost their jobs and have limited income.

Author — Finch Harper


Great video totally logical.Please forward to WHO AND UK GOVMT. THEY ARE BOTH CLUELESS.DONALD TRUMP ALSO.Not only have they totally failed to appreciate how this virus spreads, they have actually destroyed the publics belief in masks, hence we now have major refusals to accept
masks quoting totally misleading statements in the beginning. All because they did not have ppe for NHS. This still did not alter the science on masks. Now with46, 000 deaths they decide they may be useful after 6 months maligning people who wear them. You couldn't make it up could you?

Author — anthony wilson


I’m learning so much from the trusted expert guests in these Thursday talks. Thanks for sharing!

Author — Jackie L


Working in the NHS as a therapist, who would normally spend between 60 - 90 mins face to face in a small room, so less physical contact, but probably longer duration than my medical and nursing colleagues, I’d be really interested to see more data about the impact of time on risk of infection.

Author — Tania Thorn


Though it seems late to see this, I appreciate all your efforts. When I tried to persuade my surroundings with the functioning of masks in March, few people trusted me (some of them considered wearing masks as cultural difference, which sounds ironic and "racist" to me today). Hopefully, the words from these experts can change their values. Otherwise, just let them go.

Author — Adrian Yang


Austria has seen no difference when taking up and later dropping it again

Author — annelbe ab


Thank you for this life saving information 🙏🏼💜

Author — Lupus Positive LIFE Glendora


English observer grateful to you for your very informative discussion, here in U.K. the government have made a complete hash of their Covid-19 policies which is probably why we have the highest death rate in Europe, if, that is, one can believe the figures. I am very interested to see what will happen when a new strain of seasonal flu combines with covid this coming

Author — Tony D.


Dr. Gandhi mentioned that N95 can be worn for giving nebulizer treatments. I understand many nurses in NYC and other places didn't give breathing treatments because it aerosolized COVID-19. These poor people who couldn't breathe were given nothing to help. I can't imagine how they must have died, slowly suffocating. :(

Author — BM


Thank you. Best to obey ALL safeguards...and pray. "O Lord, protect us from what lieth in front of us and behind us, above our heads, on our right, on our left, below our feet and every other side to which we are exposed. Verily, Thy protection over all things is unfailing." ~ Baha'i Prayer

Author — Francis Mausley


The reason I don't have covid is I wasn't tested for it lol.

Author — William Dillon