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

Fortaleza, Cristiane Ravagnani; Souza, Lenice do Rosário de; Rúgolo, Juliana Machado; Fortaleza, Carlos Magno Castelo Branco

doi:10.1590/0037-8682-0527-2020

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Review Article • Rev. Soc. Bras. Med. Trop. 53 • 2020 • https://doi.org/10.1590/0037-8682-0527-2020 copy

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

Authorship SCIMAGO INSTITUTIONS RANKINGS

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

Reference	Fabrics	Methods	Relevant results
Konda 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.	N95, surgical masks cotton, chiffon, flannel natural silk, nibrids (cotton/chiffon, cotton/silk, cotton/flannel)	Mechanical challenge with NaCl aerosols, at 2 cubic feet per minute (CFM) flow rate	Filtering efficacy was generally high for particles greater than 300 nm. Filtering properties of N95 respirators and surgical masks for particles measuring less than 300 nm fell from 85±15 to 34±15 and 76±22 to 50±7, respectively, when gaps were present (a situation similar to innapropriat fitting). For other fabrics, the filtering efficacy increased with the number of layers and was high for cotton/chiffon, cotton/silk and cotton/flannel hybrid masks.
Lustig et al.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.	N95, Cellulose-filter masks, white denim, cotton (both original fabrics and made from clothes), flannel	Mechanical challenge with virus-like inanimate particle aerosols, 14 L/min flow	Results were compared with the efficacy of N95 respirators. Higher efficacy : cellulose filter masks, two-layer denim, hybrid fabrics containing four-layer Kona cotton. Similar efficacy: four-layer Kona cotton, two-layer fabrics (cloth tower, white flannel, heavy 100% cotton T-shirt, flannel lab coat, and other hybrid fabrics). Lower efficacy: three or fewer layers of Kona cotton, one-layer fabrics (cotton, flannel, propylene, or hybrid).
Zhao et al.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.	Propylene used in healthcare workers’ personal protective equipment. Household materials (cotton from pillow cover, T-shirt and sweater), polyester (from toddler wrap), silk (from napkins), nylon (from exercise cloths), cellulose (from paper towels, tissue paper and copy paper)	Mechanical challenge with NaCl aerosols, at flow rate of 32 L/min. Filtering efficacy measured for different times of exposure	Most common fabric presented low-to-moderate filtering efficacy for short periods. That efficacy can be increased by fabric density (g/m²), or decreased with humidity or changes in pore sizes due to washing and drying.

Reference	Studies included	Literature bases	Interventions	Outcomes	Meta-analysis	Findings
MacIntyre & Chughtai³³33. 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.	8 RCTs on the use of masks by susceptible exposed healthy persons in the community	MedLine Embase	6 RCTs: Surgical masks or PFF2 respirators 2 RCTs: Cloth masks (In 7 RCTs, efficacy of hand hygiene was also tested)	Laboratory-confirmed influenza Influenza-like illnesses	No	Two studies found efficacy of surgical masks and PF2 respirators in subgroup analysis (but not intention-to-tread analysis). Four studies found varied efficacies of masks when combined with hand hygiene intervention, but not for masks alone. Two studies did not find any significant impact of mask use.
	5 RCTs on the use of masks by sick persons		All studies involved use of surgical masks	Laboratory-confirmed influenza Influenza-like illnesses Seasonal coronavirus	No	One study found efficacy of masks. One study found efficacy associated with adherence, but not in intention-to-treat analysis. Three studies found no impact of mask use.
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]	5 RCTs 3 observational studies All studies listed above involved use by susceptible exposed persons in the community	PubMed, Web of Science, Cochrane Library Chinese National Knowledge Infrastructure (CNKI) VIP (Chinese) database	Even though some studies included other interventions, only the isolated impact of mask use was analysed. 6 out of 8 studies included involved the use of surgical mask.	Laboratory-confirmed respiratory virus infection	Yes	Even though only three studies found protective impact, the meta-analysis found an overall risk ratio [RR] of 0.43 (95%confidence interval [CI], 0.36-0.79). The findings suggest an average 47% protection.
Chout 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]	12 RCTs 3 observational studies	Multiple electronic databases, including the World Health Organization COVID-19 database and medRxiv preprint server	Use of masks (mostly surgical)	RCTs: Laboratory-confirmed influenza, Influenza-like illnesses Observational: SARS-1, MERS, SARS-Cov-2	No (but rigorous analysis of quality of evidence and biases conducted)	1 out of 12 RCTs found some evidence for protection against respiratory viruses. Observational studies supported some protection against SARS-1 and MERS, but evidence for SARS-Cov-2 is still lacking.
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.	No RCT 3 observational studies	MEDLINE, PubMed, Embase, CINAHL the Cochrane Library, COVID-19 Open Research Dataset Challenge, COVID-19 Research Database (WHO), Epistemonikos EPPI Centre living systematic map of the evidence, ClinicalTrials.gov, WHO International Clinical Trials Registry Platform, (also relevant documents on the websites of governmental and other relevant organisations, reference lists of included papers, and relevant systematic reviews)	Several nonpharmaceutical interventions were analyzed, but only masks were of interest to our review. In all studies relevant to this review (i.e., studies in the community setting), the overall use of masks (regardless of mask type) is analyzed	All comparative studies focused on SARS-1(No study focusing on MERS or COVID-19)	Yes	2 studies found protective effect of mask use. The meta-analysis found overall RR of 0.56 (95%CI, 0.40-0.79). Average protection of 44%.

Prevention aspects	Advices
Physical properties	● Masks should have at least two layers of fabric (preferably cotton, tricoline or nylon).
	● They should have elastics to attach or straps to tie, ensuring a secure and firm fit close to the face.
	● Reasonable approximate measurements of the fabric are 21 cm high by 34 cm wide. However, they can vary according to the size of the face, and must cover the nose and mouth.
Mask handling	● Before putting the mask on, one should perform hand hygiene (alcohol-gel hub or extensively washing with water and soap).
	● Masks and for individual use and must not be shared.
	● While wearing the mask, one should avoid touching it.
	● The mask should be used for a maximum of two hours. After that time, it should ideally be changed (It is advised that for long exposures at least two masks are available).
	● In case of exchange, the used mask should be kept in a plastic waterproof bag.
	● The mask should be removed from the back to the front, never touching the outer surface.
	● Used masks should be washed with soap and water and ideally soaked for 20 minutes in hypochlorite (bleach) of 2 to 2.5% concentration. It is advised that masks are discarded after being washed several times.
	● Masks should be discarded whenever it shows signs of deterioration or impaired functionality.
Complementary issues	● Maintain social isolation and respiratory etiquette, covering the mouth and nose with the inside of the elbow when coughing or sneezing.
	● Kisses, hugs and handshakes should be avoided.
	● People with flu-like conditions must stay home (except for medical care, in which case they must wear surgical masks).
	● Under no circumstances should the cloth mask be used by health professionals in dealing with suspected or confirmed cases of COVID-19.

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[1] Corresponding author: Carlos Magno Castelo Branco Fortaleza. e-mail:carlos.fortaleza@unesp.br