Despite dramatic advances in prevention and treatment, people are still getting sick and dying as COVID-19 becomes a “flu season” that will not let go. Is this our future? Will we forever be waiting for newer vaccines and antiviral drugs with bated breath?
If we step back and view this conundrum from the perspective of infectivity rather than infection, there may be a way out. Coronaviruses and some other viral respiratory pathogens, including influenza, are riboviruses. They are tiny lipid bundles, virions, that have a few proteins on the surface and contain RNA for a genetic code but not much else. Left to themselves, little happens. However, if they manage to attach to a target cell and insert their RNA, they commandeer the cell’s metabolic machinery to do their malevolence. These virions get to their target cell because we inhale them either aerosolized or carried in droplets.
Infectivity of respiratory riboviruses, and probably severity of disease, is dose dependent. The more virions one inhales the more likely one is infected. That is the reasoning behind physical distancing and masking; the former to decrease the density of aerosolized virions in ambient air, the latter to trap infectious droplets. Both rationales are imperfect even in the hospital environment1: riboviruses virions can maintain infectivity in air currents that keep them afloat. Trapped droplets evaporate releasing virions that can pass through the pores of N95 masks unless enmeshed in the masking material itself. Furthermore, infected individuals can spew virions even if asymptomatic.2
These limitations are of little concern out of doors where droplets are dispersed and aerosols quickly diluted, but not indoors. Modern architecture and civil engineering consider turnover of air in built environments. Heating, ventilation, and air-conditioning systems are designed as a compromise between the need to recirculate air for the sake of efficient heating/cooling while turning to filters and air exchanges for the sake of air purity, particularly with regard to inert particulate materials. These modifications are effective for particles larger than virions, such as dusts and bacteria but also imperfect even in hospitals.3 In most hospitals, certain rooms are designed as “reverse flow” rooms for patients with contagious diseases such as active tuberculosis with exhaust mechanisms that expel infectious air outside the building. Aside from these rooms, ribovirus virions, are largely free range.
Nearly all of us spend much of our time indoors, in a built environment. Most workplaces and domiciles are not designed to abrogate ribovirus infectivity. However, they could be. They could be retrofitted with exhausts, fans, and/or vents, resulting in enough ambient turnover to decrease the density of airborne pathogens. Mechanical engineers call this “displacement ventilation.” Furthermore, the loss in efficiency of heating and cooling is more than recovered in the savings from constructing buildings that no longer require the space between floors to accommodate duct work. In “flu season” perhaps a modest decrement in ribovirus density would be all it takes to render our fears of “yet again” more fatuous. Testing this inference is requisite but is a surmountable challenge from a scientific vantage. All we would need to do is to retrofit some workplaces for displacement ventilation, leave other similar workplaces unchanged, and see whether it makes a difference in sickness absence in the next flu season. Proving this benefit is more a challenge from a sociopolitical vantage given the investment in pharmaceutical promise.
A century ago, it was common sense that “fresh air” was salutary. Every grandmother knew that. A Nobel Prize was awarded to a Danish scientist for treating one form of tuberculosis with sunlight and another prize to Thomas Mann for describing the treatment of tuberculosis on a Magic Mountain. Beds were moved out of doors in the 1918 Spanish flu epidemic. Probably, grandmothers knew best.
1. Birgand G, Peiffer-Smadja N, Fournier S, Kerneis S, Lescure F-X, Lucet J-C. Assessment of air contamination by SARS-CoV-2 in hospital settings. JAMA Netw Open
2. Johansson MA, Quandelacy TM, Kada S, et al. SARS-CoV2 transmission from people without COVID-19 symtpoms. JAMA Netw Open
3. American Society of Heating. Refrigerating and air-conditioning engineers. Position document on infectious aerosols. Available at: http://www.ashrae.org
. 2020; 1–20. Accessed September 14, 2022.