COVID-19: What we talk about when we talk about masks

Cristiane Ravagnani Fortaleza Lenice do Rosário de Souza Juliana Machado Rúgolo Carlos Magno Castelo Branco Fortaleza About the authors

Abstract

Even though most current recommendations include the general use of masks to prevent community transmission of SARS-Cov-2, the effectiveness of this measure is still debated. The studies on this policy include physical filtering tests with inanimate microparticles, randomized clinical trials, observational studies, ecological analyses, and even computational modeling of epidemics. Much of the so-called evidence is inferred from studies on different respiratory viruses and epidemiological settings. Heterogeneity is a major factor limiting the generalization of inferences. In this article, we reviewed the empirical and rational bases of mask use and how to understand these recommendations compared to other policies of social distancing, restrictions on non-essential services, and lockdown. We conclude that recent studies suggest a synergistic effect of the use of masks and social distancing rather than opposing effects of the two recommendations. Developing social communication approaches that clarify the need to combine different strategies is a challenge for public health authorities.

Keywords:
COVID-19; Epidemiology; Prevention; Masks; Lockdown

INTRODUCTION

The need for urgent measures to control the COVID-19 pandemic is compelling scientific research to rapidly produce results that support public policies11. Fortaleza CMCB. Emergency science: Epistemological insights on the response to COVID-19 pandemics [published online ahead of print, 2020 May 11]. Infect Control Hosp Epidemiol. 2020;1-2. doi:10.1017/ice.2020.209.
https://doi.org/10.1017/ice.2020.209...
. Scientific inferences and expert opinions have been immediately translated into recommendations, which often change in weeks. The use of masks by the general population is a typical example22. Wang J, Pan L, Tang S, Ji JS, Shi X. Mask use during COVID-19: A risk adjusted strategy [published online ahead of print, 2020 Jun 25]. Environ Pollut. 2020;266(Pt 1):115099.. Given the risk of shortage of personal protective equipment (PPE) for healthcare workers (HCWs) in the early stages of the pandemic, the World Health Organization (WHO) emphasized the “lack of evidence” on the benefit of the use of masks by the general population33. World Health Organization. Rational use of personal protective equipment for coronavirus disease (COVID-19) and considerations during severe shortages. Interin guidance, April 6th 2020. Geneva: WHO, 2020. 28p.. This view of the WHO led to severe criticism, and the guidelines changed extensively over the weeks. Still, the organization was especially careful in using the term “advice” rather than “recommendation” for the universal use of cloth masks44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p..

Despite the success of the popular “#mask4all” campaign (https://masks4all.co/), preventive policies must rely on something stronger than public opinion. Herein, we reviewed the scientific results on the effectiveness of masks for preventing SARS-Cov-2 transmission in community settings; additionally, the current “evidence” is critically appraised and the rationale behind the inclusion of this strategy in public health policies is provided.

THE FUNDAMENTAL QUESTION: HOW IS SARS-COV-2 TRANSMITTED?

Due to the current absence of a vaccine or effective chemoprophylaxis, prevention of COVID-19 relies on so-called “non-pharmaceutical” measures55. Ali ST, Wang L, Lau EHY, Xu XK, Du Z, Wu Y, et al. Serial interval of SARS-CoV-2 was shortened over time by nonpharmaceutical interventions [published online ahead of print, 2020 Jul 21]. Science. 2020; eabc9004. doi:10.1126/science.abc9004.
https://doi.org/10.1126/science.abc9004...
. These strategies are aimed at breaking epidemiological chains, and are, therefore, highly dependent on the knowledge about the routes of SARS-Cov-2 transmission.

Extensive research has focused on this issue66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
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. However, to be able to propose effective ways of prevention, we must first differentiate between the dominant transmission routes responsible for maintaining and expanding the pandemic and other routes that theoretically play secondary (if any) epidemiological roles.

The latter category involves fecal-oral transmission and contamination routes through inanimate fomites. The possibility of acquiring SARS-Cov-2 from surfaces and clothes has been supported by the persistence of viable viruses, documented over a period ranging from hours to several days77. Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564-7.. However, the presence of pathogens on a surface is only one of several criteria required to ascertain that fomites are epidemiologically relevant, and there is no substantial evidence linking that route of transmission with individual cases or outbreaks66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
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,88. Centers for Diseases Control and Prevention. Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). Atlanta, GA: CDC, 2003. 241p.. Given the severe economic implications (such as extensive advertising and selling of sanitizers) and the likelihood of a deleterious shift of focus in preventive measures, the United States Centers for Diseases Control and Prevention (CDC) has stated that “touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes (…) is not thought to be the main way the virus spreads (…)”99. Centers for Diseases Control and Prevention. How COVID-19 Spreads. Atlanta GA: CDC, 2020. [Updated 2020 July 9; Cited 2020 July 22; available from: [Updated 2020 July 9; Cited 2020 July 22; available from: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html ].
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. Having said this and recognizing the paucity of reports on mother-to-child transmission (e.g., vertical transmission through breastfeeding) or acquisition through blood transfusion66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
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, we can move on to respiratory droplets and aerosols.

The topic of transmission is of crucial importance in healthcare settings. Current isolation precautions and recommendations are classified differently for transmission from respiratory droplets and aerosols1010. Siegel JD, Rhinehart E, Jackson M, Chiarello L, the Healthcare Infection Control Practices Advisory Committee. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings. Atlanta, GA: CDC , 2007. 206p.. Droplets usually have diameters greater than 5-10 μm and spread over a distance of approximately 1 m when an infected person speaks, sneezes, or coughs. Therefore, close proximity is required for transmission. Furthermore, the use of surgical masks by healthy persons suffices to ensure their safety (and this is of major importance in healthcare settings). In aerosol (airborne) transmission, very small droplets (<5 μm) from the infected persons spread over large distances and remain suspended in the air for a long time. In healthcare settings, this leads to the need for healthy workers and visitors wearing N95 masks and undergoing preferential isolation in negative-pressure rooms66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
https://www.who.int/news-room/commentari...
,1010. Siegel JD, Rhinehart E, Jackson M, Chiarello L, the Healthcare Infection Control Practices Advisory Committee. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings. Atlanta, GA: CDC , 2007. 206p..

It is generally accepted that SARS-Cov-2 spreads primarily through droplets and occasionally through aerosols mainly produced after healthcare procedures involving the airways33. World Health Organization. Rational use of personal protective equipment for coronavirus disease (COVID-19) and considerations during severe shortages. Interin guidance, April 6th 2020. Geneva: WHO, 2020. 28p.,44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p.. It is unclear if aerosols can be generated in the community setting, but some activities such as singing and performing physical exercise have been suspected to promote airborne transmission66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
https://www.who.int/news-room/commentari...
.

FILTERING PROPERTIES: LESSONS FROM PHYSICAL TESTING

Though the use of masks dates back to the archetypical “Plague Doctor”1111. Wikipedia. Plague doctor. [Update data unavailable; Cited 2020 July 22; available from: https://en.wikipedia.org/wiki/Plague_doctor].
https://en.wikipedia.org/wiki/Plague_doc...
and was extensively documented during other epidemics1212. Zinsser H. Rats, lice and history. A chronicle of pestilence and plagues. New York: Black Dog & Levenhal, 1963. 301p.,1313. Kohn GC. The Wordsworth encyclopedia of plague and pestilence. Hertfordshire: Wordsworth, 1991. 408p., studies on the physical characteristics and filtering capacity of different fabrics are rather recent. Not surprisingly, research conducted in the past 2 decades has focused on the properties of N95 respirators1414. Huang C, Willeke K, Qian Y, Grinshpun SA, Ulevicius V. Method for measuring the spatial variability of aerosol penetration through respirator filters. Am Ind Hyg Assoc J. 1998;59(7):461-5.,1515. Qian Y, Willeke K, Ulevicius V, Grinshpun SA. Particle reentrainment from fibrous filters. Aerosol Sci Tech. 1997;27(3):394-404.,1616. Qian Y, Willeke K, Grinshpun SA, Donnelly J, Coffey CC, Qian Y, Willeke K, Grinshpun SA, Donnelly J, Coffey CC. Performance of N95 respirators: filtration efficiency for airborne microbial and inert particles. Am Ind Hyg Assoc J . 1998;59(2):128-32. and surgical masks1717. Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T, Grinshpun SA. Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks? Am J Infect Control. 2006;34(2):51-7.. The occupational risks posed by droplets (e.g., Neisseria meningitidis1818. Pollard AJ, Begg N. Meningococcal disease and healthcare workers. BMJ. 1999;319(7218):1147-8.) or aerosol-transmitted (e.g., Mycobacterium tuberculosis1919. Wang G, Xu J, Huang B, Gao S, Zhuang Y, Wang K, et al. Epidemiological characteristics of pulmonary tuberculosis among health-care workers in Henan, China from 2010 to 2017. BMC Infect Dis. 2020;20(1):484.) pathogens have been matters of concern since the late 20th century. This concern was amplified with the emergence of avian influenza (H5N1) and the H1N1 pandemic in 20092020. Lietz J, Westermann C, Nienhaus A, Schablon A. The Occupational Risk of Influenza A (H1N1) Infection among Healthcare Personnel during the 2009 Pandemic: A Systematic Review and Meta-Analysis of Observational Studies. PLoS One. 2016;11(8):e0162061.. It is also worth noting that HCWs were highly affected during the SARS outbreaks in 20032121. Possamai MA. SARS and health worker safety: lessons for influenza pandemic planning and response. Healthc Pap. 2007;8(1):18-55.. These aspects, together with the obvious requirement of healthy doctors and nurses caring for patients during epidemics and pandemics, justify the focus on the filtering properties of N95 and surgical masks in hospitals and outpatient units1414. Huang C, Willeke K, Qian Y, Grinshpun SA, Ulevicius V. Method for measuring the spatial variability of aerosol penetration through respirator filters. Am Ind Hyg Assoc J. 1998;59(7):461-5.,1515. Qian Y, Willeke K, Ulevicius V, Grinshpun SA. Particle reentrainment from fibrous filters. Aerosol Sci Tech. 1997;27(3):394-404.,1616. Qian Y, Willeke K, Grinshpun SA, Donnelly J, Coffey CC, Qian Y, Willeke K, Grinshpun SA, Donnelly J, Coffey CC. Performance of N95 respirators: filtration efficiency for airborne microbial and inert particles. Am Ind Hyg Assoc J . 1998;59(2):128-32.. An interesting review of research methods and results was published by Rengasami et al2222. Rengasamy A, Zhuang Z, BerryAnn R. Respiratory protection against bioaerosols: literature review and research needs. Am J Infect Control . 2004;32(6):345-54.. Since HCWs are of secondary importance to our article, we will discuss a single and exemplary study. In light of previous research on inanimate particles2323. Balazy A, Toivola M, Reponen T, Podgórski A, Zimmer A, Grinshpun SA. Manikin-based performance evaluation of N95 filtering-facepiece respirators challenged with nanoparticles. Ann Occup Hyg. 2006;50(3):259-69., Balazy et al.1717. Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T, Grinshpun SA. Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks? Am J Infect Control. 2006;34(2):51-7. examined the efficacy of two types of N95 respirators and two types of surgical masks using aerosols containing the bacteriophage MS2. The aerosol particles had different sizes and were tested in two airflow velocities: 30 L/min (simulating HCW breathing during light workload) and 85 L/min (simulating HCW inhaling during heavy workload). They found a significantly high filtering capacity with N95 respirators. However, even those respirators allowed the penetration of a significant quantity of viruses when expelled in the form of very small particles or when challenged with 85 L/min airflow. Thus, any type of protective mask, no matter the certification, is far from being absolutely safe44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p.,2222. Rengasamy A, Zhuang Z, BerryAnn R. Respiratory protection against bioaerosols: literature review and research needs. Am J Infect Control . 2004;32(6):345-54.,2323. Balazy A, Toivola M, Reponen T, Podgórski A, Zimmer A, Grinshpun SA. Manikin-based performance evaluation of N95 filtering-facepiece respirators challenged with nanoparticles. Ann Occup Hyg. 2006;50(3):259-69..

It has been widely stated by health agencies that the use of surgical masks of respirators by the general population can lead to shortage of these resources in healthcare settings33. World Health Organization. Rational use of personal protective equipment for coronavirus disease (COVID-19) and considerations during severe shortages. Interin guidance, April 6th 2020. Geneva: WHO, 2020. 28p.,44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p.,99. Centers for Diseases Control and Prevention. How COVID-19 Spreads. Atlanta GA: CDC, 2020. [Updated 2020 July 9; Cited 2020 July 22; available from: [Updated 2020 July 9; Cited 2020 July 22; available from: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html ].
https://www.cdc.gov/coronavirus/2019-nco...
. Besides health agencies, even the popular “#mask4all” campaign (https://masks4all.co/) has recommended the use of cloth masks in community settings. This opens avenues for studies focusing on the filtering capacity of various types of fabrics used in the manufacture of homemade masks.

In the immediate pre-pandemic era (i.e., in 2019), Neupane et al.2424. Konda A, Prakash A, Moss GA, Schmoldt M, Grant GD, Guha S. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano. 2020;14(5):6339-47. performed an optic microscopic analysis of cloth masks and compared the findings with those of surgical masks. To determine the filtering efficiency, they wrapped petri dishs with the masks and exposed them to environmental air (in central Katmandu, Nepal) and counted the particles on each side of the fabric afterwards. The filtering efficiency ranged from 63% to 84% for cloth masks and 94% for surgical masks. They were significantly associated with the density and size of the pores in each fabric. In addition, the repeated performance of washing and drying masks altered the pore size and decreased the filtering efficiency by more than 25%. Thus, the lack of standardized protocols on fabrics and particle size could lead to the possible overestimation of mask efficiency. However, the decline in filtering capacity with the processes of washing and drying must be considered when advising the public to use cloth masks during the COVID-19 pandemic.

Studies conducted during the COVID-19 pandemic have assessed the filtering properties of cloth masks made of different types of fabrics2424. Konda A, Prakash A, Moss GA, Schmoldt M, Grant GD, Guha S. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano. 2020;14(5):6339-47.,2525. Lustig SR, Biswakarma JJH, Rana D, Tilford SH, Hu W, Su M, et al. Effectiveness of Common Fabrics to Block Aqueous Aerosols of Virus-like Nanoparticles. ACS Nano . 2020;14(6):7651-8.,2626. Zhao M, Liao L, Xiao W, Yu X, Wang H, Wang Q, et al. Household Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric Charging. Nano Lett. 2020;20(7):5544-52.. A schematic view of the operational aspects and results is presented in Table 1. Briefly, efficiency varied from 5% to more than 90% and was associated with the fabric and the number of layers in the mask. We must understand those findings in the current view of emergency science11. Fortaleza CMCB. Emergency science: Epistemological insights on the response to COVID-19 pandemics [published online ahead of print, 2020 May 11]. Infect Control Hosp Epidemiol. 2020;1-2. doi:10.1017/ice.2020.209.
https://doi.org/10.1017/ice.2020.209...
,2727. Schwarz M, Scherrer A, Hohmann C, Heiberg J, Brugger A, Nuñez-Jimenez A. COVID-19 and the academy: It is time for going digital. Energy Res Soc Sci. 2020;68:101684., that is, recommendations can (or must) change as new research data become available.

TABLE 1:
Summary of methodological aspects and results of selected studies conducted during COVID-19 pandemic, addressing filtering efficiency of cloth masks

WHAT CAN WE LEARN FROM ANIMAL EXPERIMENTS?

Animal studies on the transmission of influenza virus have been conducted since the 1930s2828. Andrewes CH, Glover RE. Spread of infection from the respiratory tract of the ferret: I. Transmission of influenza A virus. Br J Exp Pathol. 1941;22:91-7.. Most animal models use ferrets, and studies have supported several routes of transmission: direct contact, indirect contact (fomites), droplets, and aerosols2929. Bouvier NM. Animal models for influenza virus transmission studies: a historical perspective. Curr Opin Virol. 2015;13:101-8.. Similar findings have been reported for other viruses, including coronaviruses3030. Yuan L, Tang Q, Cheng T, Xia N. Animal models for emerging coronavirus: progress and new insights. Emerg Microbes Infect. 2020;9(1):949-61.,3131. Singh A, Singh RS, Sarma P, Batra G, Joshi R, Kaur H, et al. A Comprehensive Review of Animal Models for Coronaviruses: SARS-CoV-2, SARS-CoV, and MERS-CoV. Virol Sin. 2020;35(3):290-304.. The controversial issue here is whether exposure in animal studies mimic the real-life situations of human beings. In other words, forced prolonged contact, generating aerosols with air turbulence, and other laboratory strategies are often regarded as being too artificial to have their findings translated into epidemiological policies2929. Bouvier NM. Animal models for influenza virus transmission studies: a historical perspective. Curr Opin Virol. 2015;13:101-8..

A recent study conducted by Chan et al.3232. Chan JF, Yuan S, Zhang AJ, Poon VK-M, Chan CC-S, Lee AC-Y, et al. Surgical mask partition reduces the risk of non-contact transmission in a golden Syrian hamster model for Coronavirus Disease 2019 (COVID-19) [published online ahead of print, 2020 May 30]. Clin Infect Dis. 2020; ciaa644. doi:10.1093/cid/ciaa644.
https://doi.org/10.1093/cid/ciaa644...
is of particular interest to our discussion. Briefly, the authors placed SARS-Cov-2-infected hamsters and naïve hamsters in adjacent cages. Some cages were separated from each other by a fabric similar to that used in surgical masks. The “surgical mask” partition reduced transmission among hamsters from 66% to 25%. This is an interesting finding, but two important limitations remain: (i) the concerns regarding the “artificiality” of exposure in the model and (ii) the focus on surgical masks, which have not been approved for use by the general population. However, given the ethical limitations in conducting studies on SARS-Cov-2 involving human subjects, “pre-clinical” research on this topic is welcome.

CLINICAL STUDIES: ADVANTAGES AND LIMITATIONS OF ANALOGY

Studies conducted with humans (i.e., clinical studies) are of utmost importance. Therefore, both observational studies and intervention research on the efficacy of masks have been the subject of systematic reviews (SRs) in the last few months. Acknowledging their valuable efforts, this section relies heavily on the reviews conducted by McIntyre & Chungtai3333. MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. Int J Nurs Stud. 2020;108:103629., Liang et al.3434. 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 Med Infect Dis. 2020;36:101751. [published online ahead of print, 2020 May 28], Chou et al.,3535. Chou R, Dana T, Jungbauer R, Weeks C, McDonagh MS. Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings: A Living Rapid Review. Ann Intern Med. 2020;M20-3213. [published online ahead of print, 2020 Jun 24]and Chu et al.3636. Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schünemann HJ, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet. 2020;395(10242):1973-87. Their search strategy, inclusion criteria, methods of analysis, and conclusions are presented in Table 2.

TABLE 2:
Selected systematic reviews of clinical studies addressing the effectiveness of mask use in the community

All SRs presented here were conducted rigorously. However, their rationales, research questions, searching strategies, interventions, and analysis methods (i.e., models of meta-analysis and measures of quality indicators) vary widely. Most importantly, the outcomes of included studies vary widely, including infection by several laboratory-confirmed respiratory viruses (mostly influenza, but also coronaviruses) and clinically defined influenza-like-illnesses (ILIs). Given these limitations, our trust in their conclusions and practical recommendations rely mostly on analogical reasoning.

Rothman argued that the principle of analogy of Bradford Hill’s causation criteria is the weakest, as it is highly (and perhaps inappropriately) influenced by the researchers’ creativity and imagination3737. Rothman KJ, Greenland S, Lash TL. Modern epidemiology. 3rd. Ed. Philadelphia: Lippincott William & Wilkins, 2012. 776p.. This heterogeneity also exemplifies what Stegenga3838. Stegenga J. Nedical nihilism. Oxford: Oxford University Press, 2018. 241p. termed "the malleability" of clinical research, which limits its claim of objectivity and the strength of its evidence in SRs. However, if analyzed with a rational filter, the studies presented above provide interesting insights into the use of masks. Of note, some studies identified the protective effects of early use and good adherence to the use of masks3333. MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. Int J Nurs Stud. 2020;108:103629.,3434. 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 Med Infect Dis. 2020;36:101751. [published online ahead of print, 2020 May 28],3535. Chou R, Dana T, Jungbauer R, Weeks C, McDonagh MS. Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings: A Living Rapid Review. Ann Intern Med. 2020;M20-3213. [published online ahead of print, 2020 Jun 24].

ASKING PROPER QUESTIONS TO GET PROPER ANSWERS

Most studies included in the SR cited in the previous section3333. MacIntyre CR, Chughtai AA. A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. Int J Nurs Stud. 2020;108:103629.,3434. 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 Med Infect Dis. 2020;36:101751. [published online ahead of print, 2020 May 28],3535. Chou R, Dana T, Jungbauer R, Weeks C, McDonagh MS. Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings: A Living Rapid Review. Ann Intern Med. 2020;M20-3213. [published online ahead of print, 2020 Jun 24],3636. Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schünemann HJ, et al. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet. 2020;395(10242):1973-87.carefully assessed the confounding factors, such as baseline influenza vaccination and intensity of exposure to infected persons. However, individual-based studies (except cluster-randomized trials) did not provide good adjustments for population-level exposures and outcomes. In this setting, results from ecological studies3939. Morgenstern H. Ecologic studies in epidemiology: concepts, principles, and methods. Annu Rev Public Health. 1995;16:61-81. and modeling4040. Garner MG, Hamilton SA. Principles of epidemiological modelling. Rev Sci Tech. 2011;30(2):407-16. may be of special interest.

Zhang et al.4141. Zhang R, Li Y, Zhang AL, Wang Y, Molina MJ. Identifying airborne transmission as the dominant route for the spread of COVID-19. Proc Natl Acad Sci U S A. 2020;117(26):14857-63. addressed the routes of SARS-Cov-2 spread and the effectiveness of masks by comparatively analyzing the time trends of COVID-19 in New York state and the USA. Briefly, the authors applied interrupted time series (ITS) analysis to the trends before and after three population-level interventions: (i) social distancing (recommended for the whole country in March 2020), (ii) stay-at-home recommendation (applied in March in New York and in April in the whole of the USA), and (iii) face-covering (generally by masks) recommendation (applied in New York only on April 17th, 2020). The results showed the impact of “stay-at-home”, which was further increased by the face mask recommendation. Further comparisons with time trends in Wuhan (China) and Italy supported the primary impact of mask use, in conjunction with simultaneous social distancing, quarantine, and contact tracing.

Another interesting methodological approach was devised by Howard et al.4242. Howard J, Huang A, Li Z, Tufekci Z, Zdimal V, van der Westhuizen H, et al. Face Masks Against COVID-19: An Evidence Review. An Evidence Review. Preprints 2020, 2020040203 (doi: 10.20944/preprints202004.0203.v3).
https://doi.org/10.20944/preprints202004...
, i.e., mixing SR of ecological data with computational modeling of the impact of masks on the basic reproduction number (R0) of the SARS-Cov-2. Briefly, the results indicate a synergistic effect of the physical filtering properties of mask fabrics and the proportion of the population who showed adherence to its use. In an optimal scenario, this would represent a decrease in initial R0 from 2.4 to a post-intervention reproductive number (Re) below 1. As one may be aware, sustained Re below 1 will lead to a decrease in cases and, ultimately, end the outbreak4242. Howard J, Huang A, Li Z, Tufekci Z, Zdimal V, van der Westhuizen H, et al. Face Masks Against COVID-19: An Evidence Review. An Evidence Review. Preprints 2020, 2020040203 (doi: 10.20944/preprints202004.0203.v3).
https://doi.org/10.20944/preprints202004...
. Still, Howard et al. recommend this measure in conjunction with other nonpharmaceutical strategies.

Both Zhang’s4141. Zhang R, Li Y, Zhang AL, Wang Y, Molina MJ. Identifying airborne transmission as the dominant route for the spread of COVID-19. Proc Natl Acad Sci U S A. 2020;117(26):14857-63. and Howard’s4242. Howard J, Huang A, Li Z, Tufekci Z, Zdimal V, van der Westhuizen H, et al. Face Masks Against COVID-19: An Evidence Review. An Evidence Review. Preprints 2020, 2020040203 (doi: 10.20944/preprints202004.0203.v3).
https://doi.org/10.20944/preprints202004...
approaches do not fit well in the Cochrane methodological hierarchy of generating evidence2727. Schwarz M, Scherrer A, Hohmann C, Heiberg J, Brugger A, Nuñez-Jimenez A. COVID-19 and the academy: It is time for going digital. Energy Res Soc Sci. 2020;68:101684.,4343. Keeling MJ, Rohani P. Modeling infectious diseases in humans and animals. Princeton: Priceton University Press, 2008.. However, by addressing population-level interventions and outcomes, they provide an interesting rationale for public health strategies. Most importantly, both authors recommend the use of masks “in conjunction with widespread testing, contact tracing, quarantining of anyone that may be infected, hand washing, and physical distancing…face masks are a valuable tool to reduce community transmission.”

This type of methodological humility is particularly appropriate; it emphasizes the importance of asking the right question. In brief, despite strong statements made by Zhang et al.4141. Zhang R, Li Y, Zhang AL, Wang Y, Molina MJ. Identifying airborne transmission as the dominant route for the spread of COVID-19. Proc Natl Acad Sci U S A. 2020;117(26):14857-63., no study posed a research question like “can mask use be recommended instead of social distancing/lockdown policies?” This question is hard to address even considering the extensive data that may support natural experiments. A reasonable question (e.g., “is mask use a good public health strategy in conjunction with distancing policies?”) is likely to produce answers that guide policies directed at communities, while preventing a false sense of safety (with mask use) that exposes people to high levels of risk (e.g., crowding in close places).

RATIONALE AND PRACTICAL ADVICE

Based on the discussion presented above, one may infer that the WHO is concerned about the false sense of safety and possible shortage of personal protective equipment for HCWs33. World Health Organization. Rational use of personal protective equipment for coronavirus disease (COVID-19) and considerations during severe shortages. Interin guidance, April 6th 2020. Geneva: WHO, 2020. 28p.,44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p.. Still, there is a rational argument for the universal use of masks in the community. Cloth masks may have a reasonable (though far from complete) protective impact that depends on the fabric and number of layers and is probably reduced with successive washing and drying. Based on these findings, reasonable advice for the general population is provided in Table 3. The advice complies with (but is not a copy of) WHO guidelines33. World Health Organization. Rational use of personal protective equipment for coronavirus disease (COVID-19) and considerations during severe shortages. Interin guidance, April 6th 2020. Geneva: WHO, 2020. 28p.,44. World Health Organization. Advice on the use of masks in the context of COVID-19. June 5th, 2020. Geneva: WHO , 2020. 16p.. It should be understood as a provisional guide for public policies, which can be modified in the face of novel scientific findings. Novel findings and technologies are particularly welcome. An interesting example is that of “elastomeric masks” that are made of synthetic or natural rubber and can be washed and reused4444. Chiang J, Hanna A, Lebowitz D, Ganti L. Elastomeric respirators are safer and more sustainable alternatives to disposable N95 masks during the coronavirus outbreak. Int J Emerg Med. 2020;13(1):39.. Even though agencies such as the United States Food and Drug Administration (FDA) still raise concerns about its use, they have been approved for healthcare settings as substitutes for N95 respirators during mask shortages4545. Centers for Diseases Control and Prevention. Elastomeric Respirators: Strategies During Conventional and Surge Demand Situations. Atlanta: CDC, 2020 [updated 2020 April 09; cited 2020 August 27]. Available from: Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/elastomeric-respirators-strategy/index.html .
https://www.cdc.gov/coronavirus/2019-nco...
. Since the current review focused on the use of masks outside healthcare settings, those interested in the research on elastomeric respirators can refer to recent articles and guidelines4444. Chiang J, Hanna A, Lebowitz D, Ganti L. Elastomeric respirators are safer and more sustainable alternatives to disposable N95 masks during the coronavirus outbreak. Int J Emerg Med. 2020;13(1):39.,4646. Carver R. What we talk about when we talk about love: stories. New York: Vintage, 1988. Conventional Strategies During Non-Surge Demand Situations..

TABLE 3:
General advices for manufacture and use of masks in community settings3.

FINAL REMARKS

The title of this review is a pastiche of one of Raymond Carver’s (1938-1988) famous works, “What we talk about when we talk about love”4646. Carver R. What we talk about when we talk about love: stories. New York: Vintage, 1988. Conventional Strategies During Non-Surge Demand Situations.. In that text, Caver encourages the reader to reflect on an excessively trivialized theme through the demonstration of (somewhat bizarre) situations in which love is expressed. Likewise, this review did not aim to provide exhaustive data on the topic and did not follow the guidelines for SRs or scoping reviews. Instead, we attempted to outline a multifaceted approach to scientific research that supports the use of masks by the general population. Since protection of HCWs was not the focus of this review, some discussions (e.g., reprocessing surgical masks or N95 respirators4747. Zorko DJ, Gertsman S, O'Hearn K, Timmerman N, Ambu-Ali N, Dinh T, et al. Decontamination interventions for the resuse of surgical mask personal protective equipment: a systematic review. J Hosp Infect. 2020;106(2):283-94. DOI: 10.1016/j.jhin.2020.07.007 [published online ahead of print, 2020 Jul 9]
https://doi.org/10.1016/j.jhin.2020.07.0...
) were not included in our discussion.

Our provisional conclusion is that there are more reasons for than against the use of cloth masks. The empirical findings are heterogeneous (and highly dependent on the fabrics used to manufacture masks), but the rational support for this strategy is stronger than, for instance, that for recommendations on disinfection of inanimate surfaces66. World Health Organization. Transmission of SARS-CoV-2: implications for infection prevention precautions. Geneva: WHO , 2020. [updated 2020 July 09; cited 2020 July 22]. Available from: Available from: https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions
https://www.who.int/news-room/commentari...
,77. Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564-7.,88. Centers for Diseases Control and Prevention. Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). Atlanta, GA: CDC, 2003. 241p.. However, for the sake of intellectual honesty, we choose the term “advice” over “recommendation,” similar to the WHO. Novel findings on the extraordinary natural experiment that the pandemic has introduced will surely increase our knowledge on this subject.

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Publication Dates

  • Publication in this collection
    06 Nov 2020
  • Date of issue
    2020

History

  • Received
    05 Aug 2020
  • Accepted
    24 Sept 2020
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