Utility of Cloth Masks in Preventing Respiratory Infections: A Systematic Review

Abstract

Background: Using face masks is one of the possible prevention methods against respiratory pathogens. A number of studies and reviews have been performed regarding the use of medical grade masks like surgical masks, N95 respirators etc. However, the use of cloth masks has received little attention.
Objectives: The purpose of this review is to analyze the available data regarding the use of cloth masks for the prevention of respiratory infections. We intended to use data from both clinical and non-clinical studies to arrive at our conclusion.
Methods: We used PubMed, Cochrane Library and Google Scholar as our source databases. Both clinical and non-clinical studies, which had data regarding the efficacy of cloth masks, were selected. Articles not containing analyzable data including opinion articles, review articles etc. were excluded. After screening the search results, ten studies could be included in our review.
Data relevant to our objective was extracted from each study including clinical efficacy, compliance, filtration efficacy etc. Data from some studies were simplified for the purpose of comparison. Extracted data was summarized and categorized for detailed analysis. Qualitative synthesis of the data was performed. But the heterogeneity between the studies did not allow for a meta-analysis.
Discussion: The review was limited by a lack of sufficient clinical studies. Lack of standardization between studies was another limitation.
Although cloth masks generally perform poorer than the medical grade masks, they may be better than no masks at all. Filtration efficacy varied greatly depending on the material used, with some materials showing a filtration efficacy above 90%. However, leakage could reduce efficacy of masks by about 50%. Standardization of cloth masks and appropriate use is essential for cloth masks to be effective. However, result of a randomized controlled trial suggest that they may be ineffective in the healthcare setting.

Full text

Utility of Cloth Masks in Preventing Respiratory
Infections: A Systematic Review
Agnibho Mondal1, Arnavjyoti Das2and Rama Prosad Goswami1
1Department of Tropical Medicine, School of Tropical Medicine, Kolkata
2Department of Anesthesiology & Critical Care Medicine, Institute of Medical Sciences, Banaras Hindu University
Abstract
Background Using face masks is one of the possible prevention methods against respiratory pathogens.
A number of studies and reviews have been performed regarding the use of medical grade masks like surgical
masks, N95 respirators etc. However, the use of cloth masks has received little attention.
Objectives The purpose of this review is to analyze the available data regarding the use of cloth masks
for the prevention of respiratory infections. We intended to use data from both clinical and non-clinical
studies to arrive at our conclusion.
Methods We used PubMed, Cochrane Library and Google Scholar as our source databases. Both clinical
and non-clinical studies, which had data regarding the efficacy of cloth masks, were selected. Articles not
containing analyzable data including opinion articles, review articles etc. were excluded. After screening
the search results, ten studies could be included in our review.
Data relevant to our objective was extracted from each study including clinical efficacy, compliance,
filtration efficacy etc. Data from some studies were simplified for the purpose of comparison. Extracted data
was summarized and categorized for detailed analysis. Qualitative synthesis of the data was performed. But
the heterogeneity between the studies did not allow for a meta-analysis.
Discussion The review was limited by a lack of sufficient clinical studies. Lack of standardization between
studies was another limitation.
Although cloth masks generally perform poorer than the medical grade masks, they may be better than
no masks at all. Filtration efficacy varied greatly depending on the material used, with some materials
showing a filtration efficacy above 90%. However, leakage could reduce efficacy of masks by about 50%.
Standardization of cloth masks and appropriate use is essential for cloth masks to be effective. However,
result of a randomized controlled trial suggest that they may be ineffective in the healthcare setting.
1
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Introduction
One of the commonly employed methods to prevent
the spread of any pandemic caused by air-borne res-
piratory pathogens is use of physical barrier methods
like protective clothing and mask usage. The primary
method of transmission of respiratory pathogens espe-
cially viral infections is via droplets. Physical barriers
like masks may have some benefit in preventing such
infections by preventing the droplet spread from person
to person.
At the moment of conducting this review, the
COVID-19 pandemic has been sweeping through the
globe and a number of preventive measures have been
implemented including but not limited to social dis-
tancing, hand hygiene, respiratory etiquette etc. Some
countries have even recommended the use of cloth
masks for the general population.1However, a closer
look at the available evidences is necessary regarding
the matter of cloth masks.
A 2011 systematic review and meta-analysis in the
Cochrane Database for Systematic Reviews2analyzed
results of 67 studies on the effect of physical interven-
tions to prevent the spread of respiratory pathogens.
Data from nine case control studies suggested that
physical barriers were effective in this regard. Both
surgical masks and N95 masks were found to be ef-
fective, however there was no information about the
efficacy of cloth masks.
In the time of a pandemic there is a noted scarcity
of resources, which includes medical grade masks like
surgical masks and other respirators like N95. In
such times of crisis, the policymakers especially in the
community setting may seek supplementation of these
equipments. Hence, whether cloth masks may be used
in the place of medical grade masks, needs to be an-
swered.
Cloth masks are different from medical grade masks.
They are not standardized and there is no standard
evidence based guidelines for their use in the con-
text of preventing disease transmission. There is a se-
vere dearth of evidence regarding the efficacy of cloth
masks in preventing the transmission of respiratory
pathogens. Moreover, due to their much dissimilarity
with the medical grade masks, we cannot extrapolate
the evidence from one to the other. Hence, although
the systematic review of Jefferson T et al.2concluded
that use of masks is likely to be effective in preventing
disease transmission, the same cannot be said about
the cloth masks without further evidence.
Therefore, to address this research gap, our study
aims to analyze the available evidences to find the util-
ity of cloth masks in preventing respiratory pathogen
transmission. Since only a handful of clinical studies
are available we will also take into account the non-
clinical studies which have a direct clinical implication
in this matter.
Methods
Study Question
The question we seek to answer is stated as follows
•Is cloth mask useful in preventing respiratory in-
fection?
Data Sources and Searches
We reported our study in compliance with Preferred
Reporting Items for Systematic Reviews and Meta-
Analyses (PRISMA) guidelines.3
We searched the following databases including
PubMed, the Cochrane Library and Google Scholar.
We used the following search terms
•PubMed and Cochrane Library– (mask OR
masks) AND (cloth OR fabric OR homemade OR
home-made OR (home AND made) OR impro-
vised)
•Google Scholar– allintitle: mask AND (cloth OR
fabric OR homemade OR home-made OR impro-
vised)
Two authors, AM and AD, performed the search in-
dependently and duplicate results were removed.
The results were then evaluated for eligibility by two
authors independently, first by the titles, then by the
abstracts and lastly by the full texts. References from
2
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each included study were also searched for further rel-
evant studies. The result from each author was com-
pared and any disparity was resolved through discus-
sion among all three authors.
Study Selection
The studies meeting the following criteria were con-
sidered for inclusion
•Studies evaluating efficacy of cloth masks in the
clinical settings
•Studies evaluating compliance of the subjects to
wearing cloth masks
•Studies evaluating filtration efficacy of cloth
masks
•Studies evaluating microscopic characters of the
cloth masks
We excluded the following types of papers
•Papers on opinions, hypothesis, case reports, case
series, letters and editorials
•Review articles
•Non-experimental studies such as mathematical
modelling
•Papers with unavailable full text
We did not set any time, geographic or language re-
striction for search results. The translated entries in
the databases and online translator tools were used for
non-English studies. All studies published till the date
of search were considered for inclusion.
Data Extraction and Quality Assessment
Data from individual studies were extracted for eval-
uation, including the clinical outcomes, risk ratio of de-
veloping respiratory illness, rate of compliance, filtra-
tion efficacy and microscopic characteristics. In case of
the papers, having only graphical representation of the
data, a graph digitizer was used to extract the neces-
sary data. Data from some studies were simplified to
make them comparable to other studies.
Assessment of Risk of Bias
The included randomized controlled trials were as-
sessed for risk of bias using the Risk of Bias Tool ver-
sion 2 by the Cochrane Collaboration.4Two authors,
AM and AD, performed the assessments independently
and any disagreement was resolved by discussion.
Data Synthesis and Analysis
The extracted data was summarized and categorized
based on different aspects of the research question.
Tabulation of data was done when possible. The data
from the studies were then compared to each other and
analyzed to form a conclusion.
Results
Included Studies
The literature search was performed on May 2, 2020
according to the PRISMA protocol (Figure 1). The
PubMed search yielded 143 results in total, whereas
Cochrane Library and Google Scholar produced 140
and 24 results respectively. A total number of 293
studies remained after removing duplicates.
After screening, ten studies met our inclusion crite-
ria. Among them two papers were randomized con-
trolled trials and eight were non-clinical studies. The
randomized controlled trial comparing efficacy of cloth
masks with that of surgical masks in preventing infec-
tions was performed in Vietnam.5The second paper
used the data from the first trial to assess the com-
pliance of the healthcare workers to cloth masks and
surgical masks.6Seven of the non-clinical studies mea-
sured filtration efficacy of cloth masks7–13 and the re-
maining study analyzed the microscopic properties of
cloth masks.14
Risk of bias assessment of the randomized controlled
trials is provided in table 1. However, a meta-analysis
could not be performed due to a lack of homogeneity
of the available data.
3
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Figure 1: PRISMA statement
Study Risk of Bias
Maclntyre et al.5Some concern
Chughtai et al.6Some concern
Table 1: Risk of bias assessment
4
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Clinical Efficacy
Only one randomized controlled trial evaluated cloth
masks for their efficacy in preventing infection by res-
piratory pathogens in comparison to surgical masks.
This randomized controlled trial5by Maclntyre et al.
had three arms, surgical masks, cloth masks and stan-
dard practice. The total number of participants were
1607, all of them healthcare workers. The study found
that after four weeks of follow up, the cloth masks per-
formed poorer than the surgical masks in preventing in-
fluenza like illness. The relative risk of influenza like ill-
ness was 13.25 (95% confidence interval 1.74 to 100.97)
compared to the surgical masks on intention-to-treat
analysis. However, there was no appreciable difference
between cloth masks and surgical masks regarding lab-
oratory confirmed viruses (relative risk 1.66, 95% con-
fidence interval 0.95 to 2.91).
Compliance
The compliance to cloth masks in comparison to
surgical masks was assessed by Chughtai et al.6us-
ing the data from the previous randomized controlled
trial. Compliance was defined as the use of designated
masks for 70% of the time while on hospital duties.
The authors reported a compliance rate of 56.8% in
the cloth mask arm and 56.6% in the surgical mask
arm. The multivariate analysis showed a relative risk
of 1.02 (95% confidence interval 0.97 to 1.08) which
indicates that compliance in both groups was almost
identical.
However, they also failed to show any association
between compliance and the efficacy in preventing in-
fections.
Filtration Efficacy in Laboratory Setup
Seven of the included studies had evaluated the fil-
tration efficacy of different types of cloth masks (Table
2). Four of these studies were conducted in labora-
tories with mechanical particles or droplet generators.
These particles were passed through the mask under
examination and filtration efficacy was calculated de-
pending on the percentage of particles blocked by the
mask. Two studies used healthy volunteers. One of
them8placed the detector under the mask while it was
worn by the subject and counted the ambient particles
passing through. In the other study10 the volunteers
coughed into a box with or without masks and the mi-
crobes inside the box were then cultured to estimate
the filtration efficacy.
Almost all studies showed that surgical masks and
N95 masks were superior to cloth masks, except one.
In the study by Shakya et al.11 a certain type of cloth
mask performed better than surgical masks and even
N95 masks in some cases. N95 also performed poorly
in the study by Konda et al.12 when the particle size
was less than 300 nm.
The study by van der Sande et al.8measured the fil-
tration efficacy of cloth masks on expulsion of droplets
by a person and found it to be about 14%.
Filtration efficacy of cloth masks varied depending
on the material used. A value as low as 9% was ob-
tained while the highest value was 99.5%. As per the
available data from the included studies cloth masks
had better filtration efficacy in case of larger particles
similar to surgical masks and N95 masks.
In the study by Shakya et al.11 one of the cloth
masks having an exhaust valve performed exception-
ally well in case of particles larger than 1 µm in size.
It showed a filtration efficacy of 81% compared to 78%
efficacy of the surgical mask.
Konda et al.12 assessed the filtration efficacy of 15
natural and synthetic fabrics. The best performers in
the <300 nm range were the cotton/chiffon hybrid, cot-
ton quilt, cotton/flannel hybrid and cotton/silk hybrid
with above 90% for all of them. In the range of >300
nm however, the best performers with >90% efficacy
were the double layered and single layered cotton with
600 threads per inch, cotton/chiffon hybrid, cotton-silk
hybrid and cotton quilt.
Effect of Leakage
Two studies evaluated the effect of leakage around
the masks on the filtration capacity. In both studies
the filtration efficacy dropped significantly in the pres-
ence of leakage.
5
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Study Material Particle Filtration efficacy(%)
Cloth mask Surgical mask N95 mask
Sande et al.8Tea cloth Ambient air particles 29 - 74 55 - 88 74 - 99.5
Rengasamy et al.95 types 20 - 1000 nm
(polydisperse) 10 - 26 99.9
Davies et al.10 10 homemade masks Expelled droplets
during cough 79 85
Maclntyre et al.5Cloth mask Sodium chloride particles 3 56 99.9
Shakya et al.11 3 types
PSL >1µm 48 - 80 >97 67 -95
PSL <1µm 15 - 86 63 - 69 77 - 88
Diesel 9 - 87 57 -92 29 - 82
Neupane et al.14 20 types Ambient air particles 63 - 84 94
Konda et al.12 15 types >300 nm 14 - 99.5 99.6 ±0.1 99.9 ±0.1
<300 nm 9 - 97 76±22 85±15
Ma et al.13
1 layer of
polyester cloth
+ 4 layers of
kitchen paper
Droplets containing
Avian Influenza Virus
95.15
(95% CI
90.97 - 97.39)
97.14
(95% CI
94.36 - 98.55)
99.98
(95% CI
99.98 - 99.99)
Table 2: Filtration efficacy reported by the included studies
In 1983 Cooper et al.7observed that fixation by
nylon hosiery reduced penetration up to 18% in N95
masks and 40% in cloth masks made of four layers of
handkerchief. Konda et al.12 also found that in the
presence of leakage, the efficacy of all masks decreased
by about 50% or more.
Microscopic Properties
Neupane et al.14 examined 20 different types of cloth
masks under light microscope and found that the small-
est pore size was 81 ±29 µm, whereas the largest pore
size was 461 ±108 µm. The pore density was found
to be 12 to 47 pores / 4.5 mm2. The surfaces of the
cloth masks were distorted significantly under stretch
and the pore size increased, but the surgical masks did
not show any such effect. The washing and drying of
a cloth mask was also observed to gradually decrease
its filtration efficacy (R2= 0.99). After four cycles of
washing and drying the filtration efficacy dropped by
about 20%.
Discussion
Available clinical data suggests that cloth masks are
inadequate in preventing influenza like illness in health-
care settings. However, no relationship was found be-
tween compliance and clinical efficacy. Filtration effi-
cacy of cloth masks was found to be variable between
different types of materials used in cloth masks. Fil-
tration efficacy is also reduced significantly by leakage.
The microscopic study14 of the cloth masks revealed
that the pore size of cloth masks is larger than 50 µm
(smallest pore size 81 ±29 µm). Yang et al.15 plotted
the size distribution of droplets produced by coughing
and found three peaks at 1 µm, 2 µm and 8 µm size
bands, which are much smaller than the pores in the
cloth masks.
However, the studies on the filtration efficacy of cloth
masks report a decent efficiency of cloth masks in filter-
ing out particulate matters for certain types of fabrics.
In some cases, the efficacy of cloth masks has been re-
ported to be higher than 90%. In the study by Konda
et al.12 double layered cotton with 600 threads per
inch showed a filtration efficacy of 99.5 ±0.1% in the
>300 nm particle range compared to 99.9 ±0.1% ef-
ficacy of N95 masks in the same range. Although less
than the N95 masks in most cases such high efficiency
of some types of cloth masks raises the hope of them
being useful against droplet infections.
In the filtration efficacy studies the efficiency of the
cloth masks in filtering particulate matters remained
decent even with the particles smaller than the pore
size. This may be due to multiple layers of cloths. The
electrostatic forces in the fabric threads may also play
a role.
6
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However, cloth masks are not standardized and there
is a wide range of cloth masks available with different
quality fabrics. Each of these studies used different
types of cloth masks. Which may explain the apparent
disparity among the study results. The cloth masks are
also rarely fit tested which causes significant decrease
in efficiency due to leakage, which may be up to 50%
or even more.12
In the healthcare setting, cloth masks were found to
be inadequate5in preventing influenza like illness com-
pared to the surgical masks (relative risk 13.25, 95%
confidence interval 1.74 to 100.97). However, the con-
clusion must be drawn carefully as there was no arm
without mask. It is not possible to deduce whether
the use of these masks is better than no masks. More-
over the filtration test of the cloth masks in that study
showed only 3% efficacy, so the poor performance of
the cloth masks may have been due to their quality.
The study on compliance,6however, failed to show
any relation between the infection rate and the mask
use. This result puts into question whether use of
masks has any effect on preventing infection or not.
This finding contrasted with a previous Cochrane Re-
view2in 2011. In this review, a meta-analysis of seven
case-control studies showed that the odds ratio of mask
use vs control was 0.32 (95% confidence interval 0.26
to 0.39) regarding the occurrence of infection by respi-
ratory viruses. But the question of efficacy of masks,
as a whole, is beyond the scope this review.
Despite good filtration efficacy, a poor protective ef-
fect against the infection by respiratory pathogens may
be explained by a number of reasons. First, the leak-
age around the masks may contribute significantly in
reducing the efficacy. In fact, two of the included stud-
ies7, 12 showed that it may reduce the efficacy by as
much as 50%. Another possibility is that, despite a
decently high efficacy of cloth masks the small amount
of particles passing through may be sufficient to cause
a clinical infection. However, these issues are also likely
to affect the efficacy of medical grade masks.
From the analysis of the available evidence, it is
clear that further clinical studies are needed to resolve
the apparent disparity. If such a trial is conducted
it would be necessary to use different types of cloth
masks. There is also a lack of study in the community
setting. The only available clinical study was done in a
healthcare setting and the data cannot be extrapolated
for the use of cloth masks in the community.
During a pandemic the scarcity of resources might
prevent the distribution of surgical masks to the com-
munity. The use of cloth masks may arise in times
like that. As per the available evidences use of cloth
masks may be recommended to the general population.
However, it must be ensured that the people using the
masks understand its limited efficacy against the infec-
tion, otherwise they might fall victim to a false sense
of security. Use of cloth masks should not lead to a
neglect of other infection control measures.
Evidence10 shows that cloth masks were also capa-
ble of reducing droplet expulsion during coughing com-
pared to the absence of a mask. Hence, maximum
safety with cloth masks may be obtained if both the
infected and the healthy persons were the masks.
If cloth masks are recommended for community use,
it would perhaps be advisable to standardize the masks
with usage of the materials proven to have high filtra-
tion efficacy. Leakage needs to be minimized as much
as possible. The users should also be instructed to use
the masks properly and replace them regularly rather
than repeatedly using the same mask.
In the healthcare setting, use of cloth masks can-
not be recommended. The available evidence indicates
that cloth masks are grossly ineffective in preventing
infection by respiratory pathogens in the healthcare
workers. The standard protocol in this context should
include surgical masks and respirators like N95.
Unlike the disposable surgical masks, cloth masks
are often washed and dried repeatedly and used for a
prolonged period of time. However, the study on the
microscopic structure of the cloth masks14 showed that
repeated washing and drying may reduce the quality of
the cloth mask, by almost 20% after four such cycles.
In the light of this evidence, it may be advisable to
change the cloth masks regularly rather than repeated
washing.
7
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Wearing a cloth mask for a prolonged time continu-
ously would also accumulate the respiratory pathogens
on the outer surface. This may result in self-
contamination from the mask itself. A study on the
surgical masks16 found that this effect increases with
the duration of mask wear. The effect is most likely
similar in cloth masks. We need a similar study with
the cloth masks to determine their maximum safe pe-
riod of continuous use.
Our study had several limitations. The number of
clinical studies was very small. Also, the results of the
included studies were too heterogeneous to allow for a
meta-analysis. The paper by Shakya et al.11 only had
graphical representation of the data. This data had to
be extracted by use of a graph digitizer which maybe
prone to some degree of inaccuracy. The lack of stan-
dardization of the cloth masks meant that every study
used different types of masks, which may lead to non-
comparable results and make interpretation difficult.
Conclusion
Although the filtration efficacy of cloth masks is gen-
erally lower compared to the surgical masks and N95
masks, they are capable of filtering out some fraction
of particles and hence may be better than using no
masks at all. In the community setting cloth mask may
be recommended during a pandemic caused by respi-
ratory pathogens if medical grade masks are in short
supply.
However, the randomized controlled trial showed5
that cloth masks are likely to be inadequate in the
healthcare setting, so it may be advisable to avoid rec-
ommending them to the healthcare workers. However,
more randomized controlled trials is needed in both
the healthcare and the community settings to generate
adequate evidence.
Efficacy of cloth masks varies greatly depending
on the materials used, which may be improved by
standardization of the manufacturing process of cloth
masks. Appropriate instructions for their use, proper
fitting to avoid leakage and regular change of cloth
masks are essential to maximize their protective effi-
cacy.
Funding Statement
No funding was received for this study.
Conflict of Interest
Non of the authors have any conflict of interests.
Author Contributions
AM conceived and prepared the outline of the study.
All authors were involved in the study design. AM and
AD were involved in the collection of data and served
as the first and the second reviewer. RPG acted as the
overall supervisor of the study and the third reviewer.
The first draft of the manuscript was prepared by AM
which was then further edited by RPG and AD.
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