Written by: Sid Komperla
3rd year Medical Student | University of Sheffield (Regional Representative)
Introduction
The Manchurian Plague of 1910 highlighted the immense beneficial effects face masks could potentially have in the prevention, containment, and eradication of largescale pandemics due to respiratory infections (1). Since then face masks have followed a varied trajectory, becoming a cornerstone of population health measures to control respiratory infection transmission in many Asian countries while being relatively obsolete in many other parts of the world. The current COVID-19 pandemic, however, has seen their use become universally readopted. The constant emergence of new strains of respiratory pathogens and with them, worldwide pandemics has meant that effective preventative and control measures are essential. When considering the effectiveness of face masks in controlling the transmission of respiratory infections, it is important to consider their use in different settings and in-turn by different population groups. This essay will aim to elucidate if, and to what extent, face masks are effective in controlling respiratory infection transmission in healthcare settings and community settings and what variables contribute to the differences observed.
Main Issues
Face mask effectiveness in medical settings and in healthcare workers
Understanding the effectiveness of face masks in medical and healthcare settings is crucial, as healthcare workers are constantly in close contact with patients who have confirmed respiratory infections. A systematic review and meta-analysis of 29 studies analysing the effectiveness of face masks against clinical and laboratory-confirmed respiratory outcomes in healthcare personnel found that both surgical masks and N95 respirators conferred a protective effect against respiratory illness (2). The findings showed a significant decrease in clinical respiratory illness, influenza-like illness and upper respiratory tract bacterial colonization. Another systematic review and meta-analysis of 21 studies corroborated the results of the first study, finding wearing masks reduced the risk of respiratory virus infection among healthcare workers by 80% compared to a control of no mask wear (3).
In addition to measuring the effect on overall adverse respiratory outcomes, both studies also looked at the protection face masks offered against specific respiratory infections such as SARS, influenza, and COVID-19 in healthcare workers. The results showed that there was a consistent reduction against confirmed cases of all 3 infections and both of these findings were consistent with similar research on the topic (2,3). It is important to note however that these sub-studies were done during periods of outbreak. This means that although a certain portion of this reduction in risk can be credited to face mask use, other factors such as existing public health measures, social distancing measures and increased adherence to hand washing may have also contributed to the overall reduction. Interestingly, both reviews found that there was not a significant protection against H1N1, although this was attributed to the relatively small sample sizes and multiple confounding factors (2,3).
Another variable involved is the type of mask used. Healthcare workers use both surgical masks and N95 respirators depending on setting and situation, so it is important to look into how the degree of protection differed between the two. A systematic review found that although both types of face masks decreased the incidence of respiratory infections reported, N95 respirators provided a significantly higher level of protection compared with surgical masks (2). Furthermore, a RCT comparing 3 different trial groups concluded that there was a higher level of protection against clinical infection with continuous N95 respirator use compared with surgical masks with N95 respirator use only when carrying out aerosol-generating procedures (4).
Collectively, the evidence indicates that both surgical masks and N95 respirators offer significant levels of protection against respiratory infections in healthcare workers. This likely stems from the ability of face masks to act as both PPE measures- that is to protect wearers from infectious droplets- and source control measures- blocking droplets released by the wearer (5). Medical personnel are constantly using verbal communication, as well as carrying out aerosol-generating procedures; both high risk activities for droplet transmitted respiratory infections. As droplet transmission is the predominant mode of transmission of respiratory infections, the potential benefits face masks offer becomes evident. Additionally, the studies cited have shown that there is a clear difference in the efficacy of protection between surgical masks and N95 respirators. This difference can be attributed to the fact that N95 respirators are tight-fit masks which are designed to decrease facial-seal leak whereas surgical masks are loose fit masks. N95 respirators also have a much smaller filter size which provides the wearer some protection against airborne transmission as well. Furthermore, N95 respirators are required to be fit-tested and pass filtration tests; no such protocol exists for surgical masks (5). Nevertheless, surgical masks are still a very effective barrier measure against large droplet transmissions. Finally, the evidence also points towards continuous mask use providing greater protection than intermittent or targeted mask use. This may be explained by the reduced risk of hand-to-face contact when changing or adjusting masks and protection in situations where healthcare workers may underestimate the risk of contact with infected individuals, such as asymptomatic patients or colleagues.
Face masks effectiveness in a community setting and non-healthcare workers
Although healthcare workers are at the frontline in terms of seeing and interacting with confirmed infected cases, much of the transmission that occurs during pandemics is outside the confines of healthcare facilities and thus analysing face mask effectiveness in a community setting is vital. The evidence on the efficacy of face mask in the community is much more conflicting than the evidence shown in medical settings. A systematic review of 19 studies found that in a community setting, masks were effective with or without hand hygiene in reducing the incidence of respiratory disease, although the protective effect was attenuated with proper hand hygiene measures (6). It also concluded that, based on the increased protection face masks offered in high transmission settings such as households and college campuses, they should offer an equally effective level of protection in crowded areas such as public spaces, public transport vehicles and other closed settings (6). Another similar systematic review showed that face masks work by non-healthcare workers could reduce the risk of viral infection by 56% in a public setting and 40% among household settings (7). Both of these studies, however, failed to comment on the differing degree of protection offered by different masks, specifically cloth masks which are the most commonly worn in community settings.
During the COVID-19 pandemic, the World Health Organisation has recommended that the general public wear non-surgical, trilayer masks in areas of widespread transmission and when social distancing is difficult. Unfortunately, the majority of the masks commercially available and used by the general public are simple, monolayer cloth masks. Thus, it is important to assess the efficacy of cloth masks in the prevention of respiratory disease when looking at the community population. A systematic review of 12 studies demonstrated that compared to a surgical face mask or N95 respirator, a cloth mask had a significantly lower level of protection in reducing the incidence of viral infections and was ineffective against ILI (8). Other systematic reviews of similar power have painted parallel pictures.
When considering that cloth masks are the predominant mask type used by the general public, the evidence for their efficacy is concerning. There are many possible explanations for the ineffectiveness of cloth masks when it comes to respiratory infection prevention. First and foremost, as mentioned before, many of the cloth masks used by the public are not adequate in terms of the number of layers, the type of material used and the fit of the mask. A simple monolayer, loose fitting face mask does not have the same filtering efficacy as a trilayer, well fitted face mask. One study quoted in the systematic review showed that a trilayer flannel fabric mask which is fitted to ensure minimal leak could provide up to 90% filtration efficacy (8). Additionally, although reusable masks may be more cost-effective, they have the potential to increase the wearers susceptibility to infection, as repeated washing of the face mask has been shown to reduce their effectiveness (8). Other factors which could all hinder effectiveness and increase the risk of infection are moisture retention and inappropriate handling of the mask when removing, storing, and donning it. However, despite the seemingly negative evidence, all the studies discussed have made it explicitly clear that ultimately, some protection is better than none (6,7,8). Cloth masks can and should still be used in closed and crowded spaces and in areas of high transmissibility. Furthermore, the use of cloth masks reduces the strain on the supply of surgical masks and N95 respirators which can instead be provided to healthcare staff, especially in times of shortages.
When looking at the overall effect of face masks in reducing respiratory infections in a community setting, the bottom line seems to be that face masks, particularly cloth masks, will not be enough. For maximum protection, the general public should be educated on correct mask etiquette and be compliant with proper use of them. Furthermore, use of face masks should always be complemented by proper hand hygiene and social distancing measures.
Conclusion
The reviewed evidence suggests that to answer the question of whether face masks are effective in reducing the spread of disease, it is crucial to look at it in a setting-based approach. There is strong evidence to suggest that in medical settings involving healthcare workers face masks are effective measures in reducing the incidence of respiratory disease. Furthermore, N95 respirators conferred greater protection due to their tighter fit and more efficient filtering system. The evidence for face masks in community also appeared to demonstrate increased protection, although the impact of cloth masks seems to be questionable owing to potentially inefficient design and user wear. Although some doubts have been raised about the possible pitfalls of face masks, such as an increase in risk compensation behavior, studies have shown this not to be the case (9). In conclusion, the evidence suggests that face masks are an effective preventative measure when it comes to respiratory disease, but it is important to recognise that they are just one element of an armamentarium of preventative health measures.
References
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Liang M, Gao L, Cheng C, Zhou Q, Uy J, Heiner K et al. Efficacy of face mask in preventing respiratory virus transmission: A systematic review and meta-analysis. Travel Medicine and Infectious Disease. 2020;36:101751.
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