August 2, 2020

YES: We Need To Talk About Ventilation: How is it that six months into a respiratory pandemic, we are still doing so little to mitigate airborne transmission?

I recently took a drive-through COVID-19 test at the University of North Carolina. Everything was well organized and efficient: I was swabbed for 15 uncomfortable seconds and sent home with two pages of instructions on what to do if I were to test positive, and what precautions people living with or tending to COVID-19 patients should take. The instructions included many detailed sections devoted to preventing transmission via surfaces, and also went into great detail about laundry, disinfectants, and the exact proportions of bleach solutions I should use to wipe surfaces, and how.

My otherwise detailed instructions, however, included only a single sentence on “good ventilation”—a sentence with the potential to do some people more harm than good. I was advised to have “good air flow, such as from an air conditioner or an opened window, weather permitting.” But in certain cases, air-conditioning isn’t helpful. Jose-Luiz Jimenez, an air-quality professor at the University of Colorado, told me that some air conditioners can increase the chances of spreading infection in a household. Besides, “weather permitting” made it all seem insignificant, like an afterthought.

While waiting for my results, I checked the latest batch of announcements from companies trying to assure their customers that they were doing everything right. A major U.S. airline informed me how it was diligently sanitizing surfaces inside its planes and in terminals many times a day, without mentioning anything about the effectiveness of air circulation and filtering inside airplane cabins (pretty good, actually). A local business that operates in a somewhat cramped indoor space sent me an email about how it was “keeping clean and staying healthy,” illustrated by 10 bottles of hand sanitizer without a word on ventilation—whether it was opening windows, employing upgraded filters in its HVAC systems, or using portable HEPA filters. It seems baffling that despite mounting evidence of its importance, we are stuck practicing hygiene theater—constantly deep cleaning everything—while not noticing the air we breathe.

How is it that six months into a respiratory pandemic, we still have so little guidance about this all-important variable, the very air we breathe? . . .

Strikingly, in one database of more than 1,200 super-spreader events, just one incident is classified as outdoor transmission, where a single person was infected outdoors by their jogging partner, and only 39 are classified as outdoor/indoor events, which doesn’t mean that being outdoors played a role, but it couldn’t be ruled out. The rest were all indoor events, and many involved dozens or hundreds of people at once. Other research points to the same result: Super-spreader events occur overwhelmingly in indoor environments where there are a lot of people. . . .

There are two key mitigation strategies for countering poor ventilation and virus-laden aerosols indoors: We can dilute viral particles’ presence by exchanging air in the room with air from outside (and thus lowering the dose, which matters for the possibility and the severity of infection) or we can remove viral particles from the air with filters.

Consider schools, perhaps the most fraught topic for millions. Classrooms are places of a lot of talking; children are not going to be perfect at social distancing; and the more people in a room, the more opportunities for aerosols to accumulate if the ventilation is poor. Most of these ventilation issues are addressable, sometimes by free or inexpensive methods, and sometimes by costly investments in infrastructure that should be a national priority.

Last week, I walked around the public elementary school in my neighborhood while thinking about what we could do if we took aerosol transmission more seriously. It’s a single-story building, all the classrooms have windows, some have doors that open directly to the outside, and many have a cement patio right outside. Teaching could move outdoors, at least some of the time, the way it did during the 1918 pandemic. Moreover, even when indoors or during rainy days, opening the doors and windows would greatly improve air circulation inside, especially if classrooms had fans at the windows that pushed air out. . . .

When windows cannot be opened, classrooms could run portable HEPA filters, which are capable of trapping viruses this small, and which sell for as little as a few hundred dollars. Marr advises schools to measure airflow rates in each classroom, upgrade filters in the HVAC system to MERV 13 or higher (these are air filter grades), and aspire to meet or exceed ASHRAE (the professional society that provides HVAC guidance and standards) standards. Jimenez told me that many building-wide air-conditioning systems have a setting for how much air they take in from outside, and that it is usually minimized to be energy-efficient. During a pandemic, saving lives is more important than saving energy, so schools could, when the setting exists, crank it up to dilute the air (Jimenez persuaded his university to do that).

We had an interesting discussion of this at a faculty meeting recently; to my surprise I was not the only one who had heard of Outside Air Factor, which was a big deal in public health before I was born.

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