COVID-19 Transmission: Medicine Grand Rounds at UCSF

Let's Just Get Every Face Covered

Photo by cottonbro at pexels.com

In the over decade-long history of this blog, Dan's recent post, A Tiresome SPAT, has been viewed more times than any other post we've ever written. And it's only been up 48 hours. This is a testament to Dan's ability to encapsulate the controversy regarding SARS-CoV-2 transmission in a billiant way. As I reflected on his writing, it became increasingly clear to me that the source of the controversy of whether we are dealing with droplet transmission or aerosol transmission is deeply rooted in the framework through which you're viewing the issue. These frames are associated with different values and ways of thinking, and depending on the frame utilized determines your recommmendations for mitigating transmission.

The first framework I'll describe is the medical (i.e., individual patient) frame. Imagine a patient visiting their physician and asking what they can do to best avoid COVID-19 infection. In addition to social distancing and hand hygiene, the physician would likely recommend a mask and eye protection. The physician might even recommend an N95 respirator depending on the patient's underlying conditions, the context of their exposures, and the patient's risk tolerance. In general, in this framework, risk tolerance is low, and the goal is typically to reduce the individual's risk to the irreducible minimum. This approach drives the occupational health perspective. PPE is viewed from the standpoint of efficacy--how do we provide ideal protection?

Now, let's look at the public health (i.e., population) framework. From this perspective, the goal is not necessarily to prevent every possible case of COVID-19, but rather to bring the outbreak to an end. This requires reducing the R0 to less than one. Thus, the interventions don't need to be perfect, and individual risk is tolerated to a somewhat greater degree. And in this framework, the PPE recommended is that which is most effective (i.e., how well does it work in the real world?), which factors in adherence. Let's say that face covering A is 90% efficacious, but only 20% of people are willing to wear it. On the other hand, face covering B is 60% efficacious, but 80% of people are willing to wear it. We're clearly better off with face covering B. The public health framework is driven by a utilitarian perspective--accomplishing the greatest good for the population, not for any given individual patient. 

Our recent JAMA viewpoint, Moving Personal Protective Equipment into the Communnity, in which we argue for universal face shields in the community settting, was written from a public health framework. This was perhaps not clear to the many individuals who pointed out that in some cases there could be airborne transmission of the virus for which a face shield may not work. Yes, we get that, but the epidemiology convinces us that the airborne route is a minor mechanism of transmission.

The bottom line here is that we can't let perfect be the enemy of the good. We recommend influenza vaccine every year despite an average seasonal effectiveness of approximately 40%. The best face covering is the face covering that people will wear. Though I personally favor face shields for community use, I am happy to see faces covered in almost any way possible (which is why I love the photo above). 

And if it's not bad enough that experts are not in agreeement, we have the additional problems of botched messaging by the CDC and political leaders who by intentionally sowing doubt and refusing to be good role models, make this work all the harder. Kudos to those leaders who are mandating face coverings. And my message to everyone is this: for community settings, let's just get everyone in a face covering now, whichever one works for them. After the pandemic is over, we can sort it out once and for all.