Can cloth masks protect healthcare professionals from SARS-CoV-2?
Healthcare workers have been on the frontline in dealing with the current coronavirus disease 2019 (COVID-19) pandemic. Naturally, they have been exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, at a much higher frequency than those in most other professions – especially those working in emergency services and intensive care units (ICU). Effective personal protective equipment (PPE), including medical masks, for this class of workers is a necessity.
Given the global scarcity of surgical masks, a rapid review recently appeared in the journal Annals of Family Medicine in January 2021, dealing with the potential use of cloth masks in healthcare scenarios.
The need and use of cloth masks
About 58% of primary care clinicians in the USA reported, by April 2020, that they were using homemade or used PPE. This was due to the focus on large city hospitals that were struggling to care for the severely sick among COVID-19 patients, in the first wave of the pandemic. After seven months, about a third said that they did not have PPE or had to reuse PPE to the point where it felt unsafe.
As of now, the researchers claim, all clinicians cannot access PPE to adequate levels, either from their hospitals or healthcare systems, or from the National Strategic Stockpile, because of insufficient resources. The data on appropriate PPE confuses matters further, being both conflicting and vague. This is nowhere more obvious than in the matter of mask usage, where public health organizations have executed a U-turn in their attitude on the necessity of mask use, in general.
Many individuals and healthcare systems have taken steps such as rationing PPE, reusing and recycling masks, and using homemade face protectors such as cloth masks.
Unknowns of mask use
The US Centers for Disease Control and Prevention (CDC) opinion is that cloth masks are ‘a last resort’ for clinicians, since it does not consider them to be PPE and “their capability to protect health care clinicians is not currently known.” The best design for a cloth mask in case PPE is not available, or the relative protection it offers, are both unclear.
Study parameters
The study aimed to answer the question as to whether the use of cloth masks is efficacious in reducing the risk of respiratory virus infections, including SARS-CoV-2, among clinicians. The researchers reviewed available studies, including randomized control trials (RCTs), observational and nonhuman studies.
The term ‘cloth mask’ here appears to masks made of any woven nonsynthetic or polyester fabric, and they were compared for efficacy against industrial medical or surgical masks. Their efficacy was measured in terms of filtration of bacteria or viruses, their fit, and pressure gradient. Their effectiveness was measured in terms of the protection they offer against infection in clinical settings, as shown by infection rates.
Filtration
The researchers found that among relevant studies, four found viable pathogens and one detected virus by colony formation and polymerase chain reaction (PCR), respectively. The mask material included polyester, cotton, tea towel, and scarfs, while the setting was that of a laboratory. All studies concluded that cloth limits penetration only partially, and filtered out biological materials (such as virus and bacteria) less efficiently and more variably than medical masks.
Multiple layers were more efficacious in their filtration effect. Specifically, one study showed that a single layer of polyester combined with four layers of paper towel had the same filtration efficiency as a medical mask. The study found that both polyester masks and polyester-paper towel combinations could block 95% of particles with a size similar to SARS-CoV-2, as detected by PCR. Nonetheless, the authors suggested the use of N95 respirators by clinicians.
It is noteworthy that these studies dealt with aerosolized non-coronavirus, bacterial or simulated particles. The World Health Organization (WHO) deems contact with contaminated secretions or environments, and respiratory droplets, to be the primary route of viral transmission for SARS-CoV-2, rather than aerosols. This indicates that more research is required before a firm conclusion can be made about the protective efficacy of cloth masks in the context of COVID-19.
Fit
Commercial fit systems were used in one study of cloth masks that were both made and worn by volunteers. Another used the inward leakage of particles to assess fit, comparing homemade tea towel masks to medical masks. They found that in both cases, cloth masks did offer a barrier to particles, but had worse fit than medical masks, and allowed more particle leakage. A poor fit reduces the degree of protection by allowing particles to pass through gaps between the face and the mask.
Airflow
Two human studies measured airflow through cloth masks, and found that vacuum bags and tea towels, though associated with the greatest filtration efficiency, allowed only very little airflow. This introduces difficulties with breathing and results in reduced compliance.
Effectiveness
Two studies were intended to measure the risk of infection in cloth mask users in clinical conditions. The only RCT in this area so far compared infection rates in users who used cloth masks or medical masks under both standardized and typical clinical conditions. The authors concluded that the effectiveness of masks was in question in clinical settings.
The cloth mask users in this study had more than 13 times the risk of influenza-like illness (ILI) than those who used medical masks. It is not clear whether these findings are because medical masks offer greater protection or because cloth masks are somehow harmful to the wearer. On the other hand, the medical masks used here were of low quality, and had been found by the same researchers in an earlier study to be of negligible use in preventing viral infections compared to N95 masks. This led them to conclude that the increase in ILI in cloth mask users was caused by the masks themselves.
The reasons may include poor cleaning (80% of wearers cleaned their masks at home with soap and water), moisture retention, poor filtration efficiency, and reuse. However, the actual pattern of cloth mask use was not described in the study, which makes it difficult to arrive at actual conclusions regarding their real-life use. The pathogens isolated in this study included human metapneumovirus, rhinoviruses, and influenza B virus, which differ significantly from SARS-CoV-2 in their spread and virulence.
In a study of foot-and-mouth virus, the researchers concluded that industrial and cloth masks were alike in having only a minimal effect on the total inhalation of virus.
What are the implications?
There are large lacunae in the available studies, such as the viability of the virus on mask material, and how mask users behave in comparison with non-mask users in ways that may affect virus transmission. For instance, psychologists cite the theory of risk compensation, where people tend to take more risks when they feel safer.
Given the lack of quantity and quality of literature available, this review cannot remark definitively on protection for health care clinicians from COVID-19 by cloth masks.”
However, if a primary care clinician cannot obtain PPE, the researchers say the use of a cloth mask is better than no mask, provided the wearer keeps its limitations in mind. Further research is also crucial to study the efficacy and effectiveness of cloth masks against respiratory droplets rather than aerosols alone, before N95 respirators can be claimed to be the end-all and be-all of masks in COVID-19.
Meanwhile, cloth masks must be frequently changed, paired with a plastic face shield, and washed to hospital laundry standards, if used. There is little evidence of their protective efficacy, calling for caution in their use for extended periods.
