Is There a Rationale for Routine Mask use After COVID-19?
The physical barrier, or filter, between pollution, irritants, and pathogens in the ambient environment and the airway's ports of entry of the mouth and nose makes practical sense. We have a quasi-autonomic response to irritants, ranging from reflex apnea to harsh chemicals to covering one's mouth with hands, elbows, or part of a shirt or coat when exposed to a sensed inhalational hazard. Occupational exposure to dust prompts standard use of face masks, which are similarly used in a surgical suite to protect an open wound from surgeons' and nurses' microbes. A factory worker, a painter sanding, or a surgeon wearing a mask comes as a normal sighting. When properly used, BFCs have greatly contributed to a reduction in SARS-CoV-2 transmission.[2–4] Two distinct mechanisms support this function:
Personal Protection. Occupational health professionals have long used masks and respirators to provide personal protection for the wearer from hazardous airborne particles. To achieve this purpose, highly efficient filtration of the particles in question is required. In addition, and perhaps more importantly, the device needs to fit the wearer's face to prevent hazardous particles from simply slipping around through leaks at the perimeter of the face piece. Without these features, it may lessen the benefit to the wearer, potentially (and counterintuitively) increasing risk by emboldening the wearer. 1.
Population Protection. For many years, the medical community recognized another very important function of masks and respirators when worn by caregivers: they greatly reduce the patient's exposure to potentially hazardous microbes shed by health care providers. Filtration efficiency and fit are substantially less important when BFCs are used for population protection because of the close proximity of the filtration medium to the wearer's nose and mouth and the large initial size of the emission. The effectiveness of widespread BFC use to minimize COVID-19 transmission primarily relies on the latter effect, although protection is observed both ways. 2.
The concept of wearing a mask or respirator to protect yourself is an intuitive one; however, the idea of wearing such a device to protect others is far less so. Although it may be difficult to accurately predict the fractional etiologic contribution of BFCs, handwashing, and distancing, the contribution of masks is evident. For example, in ecologic-type studies of jurisdictions with and without mask-wearing mandates, the value of masks was clear—not only against COVID virus but also influenza virus.[16,17] This was corroborated by various laboratory evaluations that showed the value of BFCs and the importance of fit.[2,3] Early in the COVID-19 pandemic, the public, as well as experts in the public health community, made decisions framed by similar intuitive expectations of the mask benefits that overemphasized personal protection while vastly underappreciating the importance of population protection.
There are many occupations in which individuals work in close physical proximity, and the use of face coverings could become a more standardized practice in these settings. The same is true for members of the public in high-density settings. Wearing masks in theaters or other indoor settings is unlikely to take hold broadly, but why shouldn't it? One does not remove Band-Aids before curtain time. Crowded public transportation, such as subways and buses, and commercial airline flights may be additional appropriate settings for continuing with BFCs.
In addition to congregate settings in hospitals where the shedding of respiratory microbes might be expected (e.g., waiting rooms in emergency rooms and physicians' offices), one may consider the value of masks in periods of higher potential exposure risks, such as flu season and periods of elevated air pollution. Flu was dramatically reduced during the COVID-19 pandemic. Should these practices, in parallel with HVAC audits and improvements, be part of the rewrite of post-COVID-19 procedures in vulnerable environments such as long-term care facilities and prisons?
In South Korea, the regular appearance of clouds of brown dust from China has long prompted widespread mask use as a natural reaction. Interestingly, sales of face masks in South Korea between the MERS and COVID-19 outbreaks reflected year-over-year increases in the absence of a pandemic and prompted a fashion movement, which undoubtedly has aided their acceptance and popularity. In North America, for example, there are periods throughout the year when particulate matter exceeds air quality standards, especially during wildfires. Given the unprecedentedly normalized state of BFC use in the general population, is now the time to highlight the potential broader benefits of BFC use?
Am J Public Health. 2022;112(6):846-849. © 2022 American Public Health Association