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Abstract

In response to the Coronavirus Disease 2019 (COVID-19) pandemic, current modeling supports the use of masks in community settings to reduce the transmission of SARS-CoV-2. However, concerns have been raised regarding the global shortage of medical grade masks and the limited evidence on the efficacy of fabric masks. This study used a standard mask testing method (ASTM F2101-14) and a model virus (bacteriophage MS2) to test the viral filtration efficiency (VFE) of fabric masks compared with commercially available disposable, surgical, and N95 masks. Five different types of fabric masks were purchased from the ecommerce website Etsy to represent a range of different fabric mask designs and materials currently available. One mask included a pocket for a filter; which was tested without a filter, with a dried baby wipe, and a section of a vacuum cleaner bag. A sixth fabric mask was also made according to the Victorian Department of Health and Human Services (DHHS) guidelines (Australia). Three masks of each type were tested. This study found that all the fabric masks had a VFE of at least 50% when tested against aerosols with an average size of 6.0 µm (VFE(6.0 µm)). The minimum VFE of fabric masks improved (to 63%) when the larger aerosols were excluded to give and average aerosol size of 2.6 µm (VFE(2.6 µm)), which better represents inhaled aerosols that can reach the lower respiratory system. The best performing fabric masks were the cotton mask with a section of vacuum cleaner bag (VFE(6.0 µm) = 99.5%, VFE(2.6 µm) = 98.8%) or a dried baby wipe (VFE(6.0 µm) = 98.5%, VFE(2.6 µm) = 97.6%) in the pocket designed for a disposable filter, the mask made using the Victorian DHHS design (VFE(6.0 µm) = 98.6%, VFE(2.6 µm) =99.1%) and one made from a layer of 100% hemp, a layer of poly membrane, and a layer of cheesecloth (VFE(6.0 µm) = 93.6%, VFE(2.6 µm) = 89.0%). The VFE of two surgical masks (VFE(6.0 µm) = 99.9% and 99.6%, VFE(2.6 µm) = 99.5% and 98.5%) and a N95 masks (VFE(6.0 µm) = 99.9%, VFE(2.6 µm) = 99.3%) were comparable to their advertised bacterial filtration efficacy. This research supports the use of fabric masks in the community to prevent the spread of SARS-CoV-2; however, future research is needed to explore the optimum design in ensuring proper fit. There is also a need for mass education campaigns to disseminate this information, along with guidelines around the proper usage and washing of fabric masks.
pathogens
Communication
Viral Filtration Eciency of Fabric Masks Compared
with Surgical and N95 Masks
Harriet Whiley * , Thilini Piushani Keerthirathne, Muhammad Atif Nisar, Mae A. F. White
and Kirstin E. Ross
Environmental Health, College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide 5001,
Australia; Thilini.Ke@flinders.edu.au (T.P.K.); Muhammadatif.Nisar@flinders.edu.au (M.A.N.);
Mae.White@flinders.edu.au (M.A.F.W.); Kirstin.Ross@flinders.edu.au (K.E.R.)
*Correspondence: Harriet.Whiley@flinders.edu.au; Tel.: +61-(08)-7221-8580
Received: 15 August 2020; Accepted: 16 September 2020; Published: 17 September 2020


Abstract:
In response to the Coronavirus Disease 2019 (COVID-19) pandemic, current modeling
supports the use of masks in community settings to reduce the transmission of SARS-CoV-2. However,
concerns have been raised regarding the global shortage of medical grade masks and the limited
evidence on the ecacy of fabric masks. This study used a standard mask testing method (ASTM
F2101-14) and a model virus (bacteriophage MS2) to test the viral filtration eciency (VFE) of fabric
masks compared with commercially available disposable, surgical, and N95 masks. Five dierent
types of fabric masks were purchased from the ecommerce website Etsy to represent a range of
dierent fabric mask designs and materials currently available. One mask included a pocket for a
filter; which was tested without a filter, with a dried baby wipe, and a section of a vacuum cleaner
bag. A sixth fabric mask was also made according to the Victorian Department of Health and Human
Services (DHHS) guidelines (Australia). Three masks of each type were tested. This study found that
all the fabric masks had a VFE of at least 50% when tested against aerosols with an average size of 6.0
µ
m (VFE
(6.0 µm)
). The minimum VFE of fabric masks improved (to 63%) when the larger aerosols were
excluded to give and average aerosol size of 2.6
µ
m (VFE
(2.6 µm)
), which better represents inhaled
aerosols that can reach the lower respiratory system. The best performing fabric masks were the
cotton mask with a section of vacuum cleaner bag (VFE
(6.0 µm)
=99.5%, VFE
(2.6 µm)
=98.8%) or a
dried baby wipe (VFE
(6.0 µm)
=98.5%, VFE
(2.6 µm)
=97.6%) in the pocket designed for a disposable
filter, the mask made using the Victorian DHHS design (VFE
(6.0 µm)
=98.6%, VFE
(2.6 µm)
=99.1%)
and one made from a layer of 100% hemp, a layer of poly membrane, and a layer of cheesecloth
(VFE
(6.0 µm)
=93.6%, VFE
(2.6 µm)
=89.0%). The VFE of two surgical masks (VFE
(6.0 µm)
=99.9% and
99.6%, VFE
(2.6 µm)
=99.5% and 98.5%) and a N95 masks (VFE
(6.0 µm)
=99.9%, VFE
(2.6 µm)
=99.3%)
were comparable to their advertised bacterial filtration ecacy. This research supports the use of
fabric masks in the community to prevent the spread of SARS-CoV-2; however, future research is
needed to explore the optimum design in ensuring proper fit. There is also a need for mass education
campaigns to disseminate this information, along with guidelines around the proper usage and
washing of fabric masks.
Keywords: cloth mask; COVID-19; public health; PPE; face mask
1. Introduction
In response to the global Coronavirus Disease 2019 COVID-19 pandemic caused by SARS-CoV-2,
there has been increasing support for the wearing of masks in community settings [
1
5
]. On 15 April 2020,
the US CDC recommended the use of cloth face covering, especially in areas of significant community
based transmission [
4
]. This was followed by the World Health Organization recommendation, on
Pathogens 2020,9, 762; doi:10.3390/pathogens9090762 www.mdpi.com/journal/pathogens
Pathogens 2020,9, 762 2 of 8
the 5 June, that masks can be used in community settings to protect oneself when in contact with an
infected individual or for source control (worn by healthy and potentially asymptomatic individuals to
prevent onward transmission) [
6
]. On the 22 July in Australia, the second wave of SARS-CoV-2 cases
in Victoria led to mandatory wearing of masks in metropolitan Melbourne and Mitchell Shire, which
was enforced by the police through the issuing of fines [
7
]. This was quickly followed by companies
across Australia recommending the use of masks for workers and customers [8].
Modeling studies support the use of masks in the community to prevent the spread of
COVID-19 [3,9]
. Eikenberry et al. [
3
] used a hypothetical mask adoption model to demonstrate
that if 80% of the community in New York wore masks in public, and the masks were 50% eective,
this could prevent 17–45% of projected number of deaths. The same study found that even masks that
are less eective could significantly reduce the number of deaths in areas with low transmission rates.
For example, in Washington if 80% of the community wore masks that were only 20% eective this
could still reduce the number of deaths by 24–65%.
Despite the evidence from modeling studies that support guidelines for mask wearing in the
community, this advice has received some backlash [
10
]. One of the main arguments against the use of
face masks in community settings is the limited availability of medical masks and the need to triage
supplies and ensure healthcare workers have adequate protection [
4
,
11
]. For example, on Twitter at
the beginning of the pandemic, the US Surgeon General urged people against buying masks for use by
healthy people [
9
]. The need to triage the use of medical supplies has led to the emerging support for
the use of fabric face masks [
4
,
6
]. However, there is currently limited evidence available regarding the
ecacy of fabric face masks to prevent respiratory infections [12].
This study used a standard method to evaluate the ecacy of currently available fabric face masks
to filter a model virus compared with surgical and N95 masks. This information will inform best
practice for fabric face mask design to protect against respiratory diseases and reduce community-based
transmission of SARS-CoV-2.
2. Results
The viral filtration eciency (VFE) of the masks tested in this study is presented in Table 1. All the
fabric masks had a VFE of at least 50% against aerosols with an average size of 6.0
µ
m (VFE
(6.0 µm)
) and
this improved to 63% against aerosols with an average size of 2.6
µ
m (VFE
(2.6 µm)
), which represents
the size of aerosols that can reach the lower respiratory system. The best performing of the fabric masks
was the cotton fabric mask with a pocket that allowed a section of vacuum cleaner bag (VFE
(6.0 µm)
=99.5%, VFE
(2.6 µm)
=98.8%) or a dried baby wipe (VFE
(6.0 µm)
=98.5%, VFE
(2.6 µm)
=97.6%) to be
inserted. Similarly eective, was the mask made from two layers of reusable shopping bag (nonwoven
polypropylene) and one layer of cotton (according to Victorian DHHS guidelines) (VFE
(6.0 µm)
=98.6%,
VFE
(2.6 µm)
=99.1%), followed by the mask made with an outer layer of 100% hemp, a middle layer
of poly membrane, and an organic cheesecloth inner (VFE
(6.0 µm)
=93.6%, VFE
(2.6 µm)
=89.0%). The
VFE of the N95 (VFE
(6.0 µm)
=99.9%, VFE
(2.6 µm)
=99.3%) and surgical masks (VFE
(6.0 µm)
=99.9% and
99.6%, VFE
(2.6 µm)
=99.5% and 98.5%) were comparable to the bacterial filtration eciency reported
on their packaging.
Pathogens 2020,9, 762 3 of 8
Table 1.
Average viral filtration eciency (VFE) of dierent types of fabric masks compared with N95,
surgical, and disposable masks determined using ASTM F2101-14 standard method with bacteriophage
MS2 as the challenge virus.
Mask
Average Viral Filtration
Eciency for an
Average Aerosol Size of
6.0 µm (VFE(6.0 µm)) (%)
[Range]
Average Viral Filtration Eciency
Calculated with the Larger Aerosols
Excluded to Give an Average Aerosol
Size of 2.6 µm (VFE(2.6 µm)) (%)
[Range]
Description 1
N95 99.9
[99.8–100]
99.3
[98.6–99.7]
KN95 (nonmedical device GB2626-2006)
Surgical 1 99.9
[99.8–100]
99.5
[98.7–99.5}
Level 1 single use surgical mask
(according to AS 4381:2015 Nelson
Laboratories, USA, bacterial filtration
ecacy (BF) average 98.2%, minimum
97.1% as per ASTMF1862)
Surgical 2 99.6
[99.3–99.8]
98.5
[98.3–98.6] Surgical face mask (99.9% BFE 2)
Disposable 1 99.9
[99.9–100]
99.7
[99.7–99.9]
Disposable face mask (nonmedical
GB/T32610-2016)
Fabric 1 54.4
[54.3–54.6]
65.8
[64.1–67.6]
Three layered masks made of 100%
cotton
Fabric 2 67.3
[54.8–92.1]
90.9
[86.5–94.3]
Denim face mask—double layer
stretchy cotton
Fabric 3 93.6
[92.1–96.3]
89.0
[86.1–90.5]
100% hemp outer layer, poly membrane
mid layer, and organic cheesecloth inner
layer
Fabric 4 50.3
[49.7–51.2]
63.6
[51.8–75.0] Two layers of 100% Mulberry Silk
Fabric 5 54.9
[55.4–55.7]
93.32
[86.9–97.7]
Washable fabric face mask with pocket
for filter made from cotton and poplin
fabric
Fabric 5 +dried baby
wipe
98.5
[97.7–99.6]
97.6
[97.0–98.5]
Fabric 5 with a dried baby wipe
inserted into the pocket
Fabric 5 +vacuum
cleaner bag
99.5
[98.9–99.9]
98.8
[96.9–99.8]
Fabric 5 with a section of a vacuum
cleaner bag inserted into the pocket
Fabric 6 98.6
[97.7–99.6]
99.1
[98.3–99.7]
Made using the Victorian DHHS design
[13]. Two layers of reusable shopping
bag (nonwoven polypropylene) and one
layer of cotton
All masks were tested in triplicate except Fabric 1, which was tested in duplicate. The average aerosol size that the
masks were tested against was 6.0
µ
m and the viral filtration eciency was calculated using this aerosol size and
then again with the larger aerosol excluded to give an average aerosol size of 2.6
µ
m to better represent the size of
aerosols that reach the lower respiratory system.
1
Description information was collected from the mask packaging
or seller website. 2Bacterial filtration eciency.
3. Discussion
Current recommendations regarding the wearing of fabric masks to reduce the spread of
SARS-CoV-2 has elicited much debate [
10
]. Concerns have been raised regarding the lack of evidence
on the ecacy of fabric masks and the potential risks, such as a false sense of security which may
lead to a disregard of social distancing measures, contamination through adjusting and touching with
contaminated hands, and improper fit [10,14,15].
This study showed that fabric masks currently available for purchase had a minimum viral
filtration eciency of 50%. This was significantly enhanced through the use of a section of a vacuum
cleaner bag or a baby wipe as a substitute for a pocket filter. There were also two designs with three
layers of dierent fabrics (Fabric 6 and Fabric 3) which performed exceptionally well with VFE above
90%. This finding supports the recommendations from The World Health Organization on making
your own fabric masks [6].
The results from this study are supported by other studies that have assessed the ability of fabric
masks to filter particles. A study on the filtration eciency of various fabrics found that the removal
eciency when one layer of fabric was used range from 5% to 80% and 5% to 95% for particle sizes of
<300 and >300 nm, respectively. However, this was significantly improved when multiple layers of
Pathogens 2020,9, 762 4 of 8
dierent combinations of fabric were used. For example cotton–silk, cotton–chion, cotton–flannel
fabric combination filtered more than 80% of particles <300 nm and >90% of particles >300 nm [
16
].
Another study conducted in Taiwan recruited volunteers with confirmed influenza A and B and
suspected COVID-19 and asked them to wear a medical mask or a three-layer cotton mask in a bedroom
or a car. The authors then measured the particles (with a size range of 20–1000 nm) located within 1 m
of the individual for 1 h and found no significant dierence in the particles produced from coughing or
sneezing between the participants wearing cotton masks and those wearing medical masks.
One limitation of this study is that it does not take into consideration the fit of the mask. Future
research is needed to examine this issue to inform the design and fit of fabric, as Konda et al. [
16
]
demonstrated that gaps due to improper fit of a fabric mask can result in over a 60% decrease in the
filtration eciency. Another limitation is that the standard method used in this study challenges masks
with the viruses traveling at the flow velocity associated with breathing. Coughing and sneezing result
in faster flow velocities which could aect the viral filtration eciency [17].
There is also the need for education campaigns aimed at informing individuals on how to wear
fabric masks. This should include details on the best design and importance of good fit. There should
also be advice on proper usage, including how to don and doface masks, the importance of not
touching masks to prevent self-contamination, and the need to wash masks in >60
C water with soap
or laundry detergent [
6
]. However, given the success of current handwashing and social distancing
campaigns, mass education on the face usage of mask is possible [1].
4. Materials and Methods
4.1. Face Masks
Fabric face masks were purchased from five Etsy retailers (www.etsy.com.au) based in Australia
and chosen at random. Five dierent types of fabric face masks were selected to best represent the
most common types of fabric masks currently available for purchase. One of the selected face masks
was designed with a pocket for a filter; however, given that there are limited filters available a dried
baby wipe and a section of a vacuum cleaner bag were tested instead of a mask filter. A final fabric
face mask was also made in accordance with the design provided by the Victorian Department of
Health and Human Services [
13
]. For comparison with the fabric face masks, two dierent types of
surgical masks, a disposable face mask and an N95 mask were also purchased in Australia. The masks
tested in this study and shown in Figure 1and descriptions are included in Table 1. Three of each of
the dierent types of masks were tested.
4.2. Conditioning of Face Masks Prior to Testing
Each mask was conditioned for a minimum of 4 h at a temperature of 21
±
5
C and relative
humidity of 85% ±10% prior to testing.
Pathogens 2020,9, 762 5 of 8
Pathogens 2020, 9, x FOR PEER REVIEW 4 of 8
90%. This finding supports the recommendations from The World Health Organization on making
your own fabric masks [6].
The results from this study are supported by other studies that have assessed the ability of fabric
masks to filter particles. A study on the filtration efficiency of various fabrics found that the removal
efficiency when one layer of fabric was used range from 5% to 80% and 5% to 95% for particle sizes
of <300 and >300 nm, respectively. However, this was significantly improved when multiple layers
of different combinations of fabric were used. For example cottonsilk, cottonchiffon, cottonflannel
fabric combination filtered more than 80% of particles <300 nm and >90% of particles >300 nm [16].
Another study conducted in Taiwan recruited volunteers with confirmed influenza A and B and
suspected COVID-19 and asked them to wear a medical mask or a three-layer cotton mask in a
bedroom or a car. The authors then measured the particles (with a size range of 201000 nm) located
within 1 m of the individual for 1 h and found no significant difference in the particles produced from
coughing or sneezing between the participants wearing cotton masks and those wearing medical
masks.
One limitation of this study is that it does not take into consideration the fit of the mask. Future
research is needed to examine this issue to inform the design and fit of fabric, as Konda et al. [16]
demonstrated that gaps due to improper fit of a fabric mask can result in over a 60% decrease in the
filtration efficiency. Another limitation is that the standard method used in this study challenges
masks with the viruses traveling at the flow velocity associated with breathing. Coughing and
sneezing result in faster flow velocities which could affect the viral filtration efficiency [17].
There is also the need for education campaigns aimed at informing individuals on how to wear
fabric masks. This should include details on the best design and importance of good fit. There should
also be advice on proper usage, including how to don and doff face masks, the importance of not
touching masks to prevent self-contamination, and the need to wash masks in >60 water with soap
or laundry detergent [6]. However, given the success of current handwashing and social distancing
campaigns, mass education on the face usage of mask is possible [1].
4. Materials and Methods
4.1. Face Masks
Fabric face masks were purchased from five Etsy retailers (www.etsy.com.au) based in Australia
and chosen at random. Five different types of fabric face masks were selected to best represent the
most common types of fabric masks currently available for purchase. One of the selected face masks
was designed with a pocket for a filter; however, given that there are limited filters available a dried
baby wipe and a section of a vacuum cleaner bag were tested instead of a mask filter. A final fabric
face mask was also made in accordance with the design provided by the Victorian Department of
Health and Human Services [13]. For comparison with the fabric face masks, two different types of
surgical masks, a disposable face mask and an N95 mask were also purchased in Australia. The masks
tested in this study and shown in Figure 1 and descriptions are included in Table 1. Three of each of
the different types of masks were tested.
N95
Surgical 1
Surgical 2
Disposable 1
Fabric 1
Fabric 2
Fabric 3
Fabric 4
Fabric 5
Fabric 5 + dried baby wipe
Fabric 5 + section of a vacuum
cleaner bag
Fabric 6
Figure 1. Masks tested in this study.
4.3. Bacteriophage MS2 Preparation
Bacteriophage MS2 (ATCC 15597-B1) was propagated using the double agar layer method. The
bottom layer (of the tryptone soya agar (TSA) Escherichia coli agar plates) consisted of TSA (Oxoid,
Basingstoke, Hampshire, UK) and the top layer consisted of 4.5 mL of soft TSA mixed with 500
µ
L
of overnight E. coli (ATCC 700891) culture (which had been incubated overnight at 37
C in typtone
soya broth (Oxoid)) and 200
µ
L of freeze thawed MS2 bacteriophage solution. The plates were then
incubated overnight at 37
C. The plaques were harvested in peptone water (Oxoid) and purified
by centrifugation at 3000 rpm for 15 min to separate the host cell debris and the bacteriophage. The
supernatant was filtered through a 0.22
µ
m Millex-GP Syringe Filter Unit (Millipore, catalog number
SLGP033RS, Tullagreen, Cork Ireland) and used as a stock solution. This stock was serially diluted in
sterile water and the concentration was determined by plating and counting plaques using the double
agar layer method described above.
4.4. Viral Filtration Eciency
Mask testing was carried out in accordance with the ASTM F2101-14 Standard Test Method for
Evaluating the Bacterial Filtration Eciency (BFE) of Medical Face Mask Materials, Using a Biological
Aerosol of Staphylococcus aureus [
18
]. However, the method was modified, and S. aureus was replaced
with bacteriophage MS2 as the test specimen. This modification was made as S. aureus has a diameter
of
1
µ
m [
19
], which is roughly 12 times larger than the SARS-CoV-2 virion (70–90 nm in diameter [
20
]).
Pathogens 2020,9, 762 6 of 8
Given, the public health significance of these findings, the precautionary principle was applied to the
experimental design and MS2 (diameter of 27 nm) was chosen as the model microorganism as it is 2–3
times smaller than SAR-CoV-2 [21].
Briefly, masks were challenged (see Figure 2for challenge apparatus) with 200
µ
L of 8.3
×
10
5
PFU/mL MS2 viral aerosols in sterile water at a flow rate of 28.3 L/min, which is within the range of
normal respiration and the limitations of the cascade impactor [
18
]. Masks were placed facing out to
test their filter ecacy when used as a personal protection device. The pressure was maintained at 35
kPa and the challenge suspension was delivered for 1 min.
Pathogens 2020, 9, x FOR PEER REVIEW 6 of 8
applied to the experimental design and MS2 (diameter of 27 nm) was chosen as the model
microorganism as it is 23 times smaller than SAR-CoV-2 [21].
Briefly, masks were challenged (see Figure 2 for challenge apparatus) with 200 µ L of 8.3 × 105
PFU/mL MS2 viral aerosols in sterile water at a flow rate of 28.3 L/min, which is within the range of
normal respiration and the limitations of the cascade impactor [18]. Masks were placed facing out to
test their filter efficacy when used as a personal protection device. The pressure was maintained at
35 kPa and the challenge suspension was delivered for 1 min.
Figure 2. Mask testing rig, set up according to the ASTM F2101-14.
Virus aerosols that passed through the mask were captured on TSA-E. coli plates within the six-
stage cascade impactor. These plates were then incubated overnight at 37 °C . The plaques were
counted and recorded as positive hole corrected [22]. The positive hole corrected counts for each of
the six stages were added together and the total from the three trials was averaged. Positive control
runs were performed in triplicate without a mask clamped into the test system to determine the
Figure 2. Mask testing rig, set up according to the ASTM F2101-14.
Virus aerosols that passed through the mask were captured on TSA-E. coli plates within the
six-stage cascade impactor. These plates were then incubated overnight at 37
C. The plaques were
counted and recorded as positive hole corrected [
22
]. The positive hole corrected counts for each of the
Pathogens 2020,9, 762 7 of 8
six stages were added together and the total from the three trials was averaged. Positive control runs
were performed in triplicate without a mask clamped into the test system to determine the number of
viable MS2 aerosols being generated. Negative control runs were performed in triplicate by collecting
a 2 min samples of air from the aerosol chamber without the MS2. The average aerosol size was 6.0
µ
m,
which is within the size range of aerosols produced by coughing (0.62–15.9
µ
m) [
23
]. Viral filtration
eciency (VFE) was calculated by comparing the average positive hole corrected PFU of MS2 captured
after the mask compared with the positive control. The VFE for each mask was also calculated with
the larger aerosol removed to provide an average aerosol size of 2.6
µ
m, which better represents the
size of inhaled aerosol that reaches the lower respiratory system and alveolar region (<3µm) [24].
5. Conclusions
This study demonstrated that typically available fabric masks have at least a 50% viral filtration
eciency and this can be increased through the use of everyday items (vacuum cleaner bag and baby
wipes) as an alternative to a disposable pocket filter or through designing fabric masks to have three
layers of dierent fabrics. This research supports the use of fabric masks in community settings to
prevent the spread of SARS-CoV-2. Future research is needed to investigate fabric mask designs that
allow the best fit, examine the influence of dierent flow velocities, and determine the availability and
costs of materials needed to make ecient masks. Additional substitutes to filters should be tested to
ensure there is global access to the supplies needed to produce eective masks and reduce the spread
of SAR-CoV-2.
Author Contributions:
Conceptualization, H.W. and K.E.R., methodology, K.E.R., H.W. and T.P.K., data curation,
T.P.K., M.A.F.W., M.A.N., H.W., writing—original draft preparation, H.W.; writing—review and editing, K.E.R.,
T.P.K., M.A.F.W. and M.A.N. All authors have read and agreed to the published version of the manuscript.
Funding:
This research received Flinders Medical Centre Foundation and Department of Innovation and Skills
(Research, Commercialization and Startup Fund) funding to establish the mask testing apparatus.
Acknowledgments:
The authors acknowledge the support given to establishing the testing apparatus from the
Flinders University Medical Devices Research Institute.
Conflicts of Interest: The authors declare no conflict of interest.
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2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... Nevertheless, some laboratories are already performing such tests [22]. In terms of research, only a few studies are available on determining the VFE of different masks [23][24][25], reporting a limited amount of experimental data. Therefore, there is a need for a study that evaluates the suitability and efficiency of different systems for determining the VFE. ...
... This allowed us to assess the performance of a non-standardized (VFE) method in relation to a standardized (BFE) method that has been used for years. Furthermore, we evaluated the suitability of bacteriophage MS2 as a model virus for different experimental setups of the VFE [24]. Thus, this study included numerous experiments, namely 17 BFE and 22 VFE experiments with 73 and 81 mask samples, respectively. ...
... Only a few other groups have worked on determining VFE in a similar setup. They either worked with MS2 [24] or phix 174 [25], which they sampled using the Andersen sampler. In addition, a completely different experimental setup was also developed to determine VFE, using the mannequin head with an aerosol source simulator and a SARS-CoV-2 pseudovirus as a model virus [23]. ...
Article
Full-text available
As a result of the COVID-19 pandemic, many new materials and masks came onto the market. To determine their suitability, several standards specify which properties to test, including bacterial filtration efficiency (BFE), while none describe how to determine viral filtration efficiency (VFE), a property that is particularly important in times of pandemic. Therefore, we focused our research on evaluating the suitability and efficiency of different systems for determining VFE. Here, we evaluated the VFE of 6 mask types (e.g., a surgical mask, a respirator, material for mask production, and cloth masks) with different filtration efficiencies in four experimental setups and compared the results with BFE results. The study included 17 BFE and 22 VFE experiments with 73 and 81 mask samples tested, respectively. We have shown that the masks tested had high VFE (>99% for surgical masks and respirators, ≥98% for material, and 87–97% for cloth masks) and that all experimental setups provided highly reproducible and reliable VFE results (coefficient of variation < 6%). Therefore, the VFE tests described in this study can be integrated into existing standards for mask testing.
... Although there is no recognized standard VFE method, a VFE method has been created by Nelson Laboratories utilizing a modified ASTM F2101 protocol; VFE testing follows the same procedure as that for BFE, with the use of a 27 nm bacteriophage phiX174 challenge organism maintained at 1,100-3,300 plaque-forming units (PFU) per test (13,16,20). Further, the NIOSH sodium chloride (NaCl) aerosol challenge is a widely accepted method for evaluating FE of respirators that must be prequalified © Journal of Public Health and Emergency. ...
... Of the 3,256 titles reviewed, 246 were selected for abstract review, from which 96 were selected for full paper review, ultimately resulting in 31 papers that met the inclusion criteria for this narrative review. These studies include 16 US studies (12,18,22,34,36,(42)(43)(44)(54)(55)(56)(57)(58)(59)(60)(61) and 15 non-US studies (i.e., Australia, Canada, China, Italy, Japan, Nepal, the Netherlands, Slovenia, South Korea, the UK) (10,11,20,29,35,40,45,47,48,(62)(63)(64)(65)(66)(67). Average FEs for FFRs, surgical/procedure masks, and makeshift material masks are illustrated in Figures 1-9. ...
... Of the included 31 studies, presented in Figures 1-9, 26 studies were conducted with particles ≤5 µm, which are defined by the WHO and CDC as aerosols or droplet nuclei (68,69). The remaining five studies (20,39,42,58,65) included test particles >5 µm, up to 20 µm, which are defined by the WHO and CDC as droplets (68,69). It is important to note that, while the WHO and CDC's standard definitions for aerosols and droplets have been widely used, the COVID-19 pandemic has brought to light inconsistencies and inaccuracies between conventional definitions used by public health agencies and those rooted in aerosol science which more accurately characterizes different transmission routes (70,71). ...
... Nevertheless, some laboratories are already performing such tests 17 . In terms of research, only few studies are available on determining VFE of different masks [18][19][20] , reporting limited amount of experimental data. Therefore, there is a need for a study that evaluates the suitability and e ciency of different systems for determining the VFE. ...
... This allowed us to assess the performance of a non-standardized (VFE) method in relation to a standardized (BFE) method that has been used for years. Furthermore, we evaluated suitability of bacteriophage MS2 as a model virus for different experimental setups of the VFE 19 . Thus, this study included numerous experiments, namely 17 BFE and 22 VFE experiments with 73 and 81 mask samples, respectively. ...
... Similar observations on the FEs of different masks were made by other groups, which found high FEs (either BFE, VFE, or particle ltration e ciency, PFE) in surgical masks and respirators, while cloth masks had different FEs, which in some cases were quite high, above 90% [18][19][20]28 . Caution should be exercised in interpreting these results, because the t of masks is usually not taken into account when FE is determined, and therefore the protection provided by the masks does not necessarily correspond to the measured FE. ...
Preprint
Full-text available
As a result of the pandemic COVID -19 many new materials and masks came on the market. To determine their suitability, several standards specify which properties to test, including bacterial filtration efficiency (BFE), while none describe how to determine viral filtration efficiency (VFE), a property that is particularly important in times of pandemic. Therefore, we focused our research on evaluating the suitability and efficiency of different systems for determining VFE. Here, we evaluated the VFE of 6 mask types (e.g., a surgical mask, a respirator, material for mask production and cloth masks) with different filtration efficiencies in four experimental setups and compared the results with BFE results. The study included 17 BFE and 22 VFE experiments with 73 and 81 mask samples tested, respectively. We have shown that the masks tested had high VFE (>99% for surgical masks and respirators, ≥98% for a material and 87-97% for cloth masks) and that all experimental setups provided highly reproducible and reliable VFE results (coefficient of variation < 6%). Therefore, the VFE tests described in this study can be integrated into existing standards for mask testing.
... Despite SARS-CoV-2 being a respiratory virus, studies on its aerosol transmission in controlled laboratory settings are still limited and standardized national or international viral filtration efficiency testing protocols are still missing [11,12]. Studies have mainly used bacteriophage and influenza viruses or inactivated viruses as challenges in filtration tests [11][12][13][14][15]. Actually, the indications to prevent transmission among the population include social distancing, the avoiding of people-gathering situations, ventilation of the indoor environment and personal and environmental hygienic measures [16]. ...
... Up to now, no standard test method is available for assessing viral filtration or inactivation efficiency of PPE for airborne SARS-CoV-2 [13]. An adapted protocol testing viral filtration and inactivation efficiency of face masks has been proposed by Nelson Laboratories starting from a Bacterial Filtration Efficiency test ASTM F2101-14 and using PhiX174 virus as a challenge [36], with mean particle size of 3.0 ± 0.3 μm and collection of the bioaerosol on a six-stage Andersen impactor; PhiX174 is also an enveloped virus considered a possible nonpathogenic surrogate for SARS-CoV-2 [37], and MS2 bacteriophages have been proposed [15,38], or inactivated virus [17]. ...
Article
Full-text available
Background: Standardized methods for testing Viral Filtration Efficiency (VFE) of tissues and devices are lacking and few studies are available on aerosolizing, sampling and assessing infectivity of SARS-CoV-2 in controlled laboratory settings. NanoAg-coated endonasal filters appear a promising aid for lowering viable virus inhalation in both adult and younger populations (e.g., adolescents). Objective: to provide an adequate method for testing SARS-CoV-2 bioaerosol VFE of bio-gel Ag nanoparticles endonasal filters, by a model system, assessing residual infectivity as cytopathic effect and viral proliferation on in vitro cell cultures. Methods: A SARS-CoV-2 aerosol transmission chamber fed by a BLAM aerosol generator produces challenges (from very high viral loads (105 PFU/mL) to lower ones) for endonasal filters positioned in a Y shape sampling port connected to a Biosampler. An aerosol generator, chamber and sampler are contained in a class II cabinet in a BSL3 facility. Residual infectivity is assessed from aliquots of liquid collecting bioaerosol, sampled without and with endonasal filters. Cytopathic effect as plaque formation and viral proliferation assessed by qRT-PCR on Vero E6 cells are determined up to 7 days post inoculum. Results: Each experimental setting is replicated three times and basic statistics are calculated. Efficiency of aerosolization is determined as difference between viral load in the nebulizer and in the Biosampler at the first day of experiment. Efficiency of virus filtration is calculated as RNA viral load ratio in collected bioaerosol with and without endonasal filters at the day of the experiment. Presence of infectious virus is assessed by plaque forming unit assay and RNA viral load variations. Conclusions: A procedure and apparatus for assessing SARS-CoV-2 VFE for endonasal filters is proposed. The apparatus can be implemented for more sophisticated studies on contaminated aerosols.
... Bacteriophages are natural antibacterial agents that lyse a specific bacterial host strain. Based on their bacterial host specificity and bacteriolytic activity, the use of bacteriophages has been suggested as an interesting virus model to assess viable airborne viruses, such as in the viral filtration efficiency of medical facemasks [23]. In this study, we used phi11 bacteriophages. ...
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Full-text available
Reducing the exposure to airborne contaminants, including bioaerosols containing viruses, is a key challenge in the context of indoor air quality. This study aims to assess the effectiveness of innovative Atmospheric Plasma Reactor (APR) technology, which can be included in air cleaner devices, as an engineering control tool for reducing the concentration of viable airborne viruses. We investigated the KillViDTM APR technology that uses ultra-high electric fields and pulsed power plasma to directly electroporate living cells and produce advanced oxidizing species in situ within the micro-droplet aerosols containing the pathogens to be treated. An experimental setup was developed in order to aerosolize a high concentration of virus suspension directly into the air cleaner, containing 3 or 6 modules of 215 atmospheric plasma micro-reactors. As a virus surrogate, we used the phi11 bacteriophage which was aerosolized using a vibrating mesh nebulizer. The viability of airborne viruses after a single pass through the air cleaner was assessed by quantifying the lysis of a specific Staphylococcus aureus host strain. We were able to demonstrate that our virucidal results were robust and showed a 5-log reduction (99.999%) in terms of virucidal activity for the 3-module configuration, while we observed at least a 6-log reduction (from an initial viral load of 9.25 × 105 PFU to 0) for the 6-module configuration.
... Since the start of the COVID-19 pandemic, there have been global concerns about the availability of medical-grade face masks and con icting evidence on the e cacy of fabric masks (Whiley et al., 2020). The CDC contends that some masks are more effective than others. ...
Preprint
Full-text available
Research Objective This study aimed to examine influential voices recommending N95 respirators during a peak in cases and deaths. Our study sought to understand whether influencers were providing accurate details about the correct type of N95 that would protect the wearer and those around them and the vital need to ensure a proper fit for the N95. Study Design Our study drew upon primary data from Twitter and retrieved n = 251,740 tweets from January 2021, which were filtered and analysed using social network analysis. The study drew upon mixed methods. Betweenness centrality was used to identify influential users recommending N95 face masks. A coding frame was developed to determine whether complete advice was provided. The tweets received as replies to each of the influencers were analysed using content analysis. Principal Findings Our study found that the most influential users recommending about N95 face masks were medical professionals and public health experts. Moreover, our data revealed that most tweets by health influencers recommending N95s did not provide further details about the correct type of N95 mask and the vital need to ensure a proper fit for the mask. Implications for Policy and Practice Healthcare influencers can play a vital role in disseminating accurate and timely information. Our study confirmed that prominent health influencers were not providing enough information about N95s. We produce three key recommendations for healthcare influencers. Our results are likely to be of interest to health services and for improving patient safety.
... 18,19 One crucial element of PPE that should probably be maintained is a surgical mask, as wearing such a mask in public has been shown to be the most efficient way to prevent transmission between people. 3 The additional benefit of using an N-95 mask over the surgical mask is still controversial 20,21 ; hence, it is reasonable that in some dental schools this mask was not considered mandatory for providing dental treatments. In addition, reducing the risk for exposure to COVID-19−positive patients can be beneficial and relatively easily done by screening patients as well as clinical staff before appointments. ...
Article
Full-text available
Objective To identify variation in specific infection prevention and control (IPC) strategies across all dental schools in Canada; and to evaluate the concordance concerning COVID-19 pandemic-related IPC strategies reported by clinic directors or IPC officers (CD/IPCO) and those reported by students, staff and faculty in the schools. Method A cross-sectional analysis within a prospective cohort study. Participants in the cohort study reported IPC strategies used in their schools during April or May 2021. Independently, CD/IPCOs reported IPC strategies in school protocols in July 2021. Results Of the 600 participants recruited, 332 participants who were involved in the provision of in-person dental care were further analyzed. Of the 16 IPC strategies investigated, only 3 were reported by CD/IPCOs to be used at all schools and another 8 strategies were used by 8 or 9/10 or by 1/10 schools, indicating concordance across schools was good for 11/16 strategies. Agreement between study participants and the CD/IPCOs varied considerably by strategy (ranging between 50-100%) and by school (ranging between 42.9-97.2%). The strategies with the highest mean agreement percentage across schools were “screening or interviewing patients before appointment for COVID-19 related symptoms” (92.7%) and “checking the temperature of the staff members at least once a day using a thermometer” (91.5%). Conclusions The level of agreement in the use of strategies between participants working in clinics and CD/IPCOs varied considerably by strategy and by school. Given the low COVID-19 infection rates in dental schools and the reported differences in IPC protocols, key strategies should be identified. Clinical Significance During the pandemic, IPC protocols in Canadian dental schools evolved rapidly. Comparing different strategies might help developing a unified standard IPC protocol.
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SARS-CoV-2 spreads via droplets, aerosols, and smear infection. From the beginning of the COVID-19 pandemic, using a facemask in different locations was recommended to slow down the spread of the virus. To evaluate facemasks' performance, masks' filtration efficiency is tested for a range of particle sizes. Although such tests quantify the blockage of the mask for a range of particle sizes, the test does not quantify the cumulative amount of virus-laden particles inhaled or exhaled by its wearer. In this study, we quantify the accumulated viruses that the healthy person inhales as a function of time, activity level, type of mask, and room condition using a physics-based model. We considered different types of masks, such as surgical masks and filtering facepieces (FFPs), and different characteristics of public places such as office rooms, buses, trains, and airplanes. To do such quantification, we implemented a physics-based model of the mask. Our results confirm the importance of both people wearing a mask compared to when only one wears the mask. The protection time for light activity in an office room decreases from 7.8 to 1.4 h with surgical mask IIR. The protection time is further reduced by 85 and 99% if the infected person starts to cough or increases the activity level, respectively. Results show the leakage of the mask can considerably affect the performance of the mask. For the surgical mask, the apparent filtration efficiency reduces by 75% with such a leakage, which cannot provide sufficient protection despite the high filtration efficiency of the mask. The facemask model presented provides key input in order to evaluate the protection of masks for different conditions in public places. The physics-based model of the facemask is provided as an online application.
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Early diagnosis and monitoring of cancer is the best way to increase the survival rate among patients with cancer. However, the current cancer screening technology is expensive and time-consuming; hence, cancer screening remains challenging. Therefore, developing a relatively inexpensive and high-performance analytical method is necessary. Especially, mutations in KRAS can be characterized as single nucleotide polymorphism mutations. Therefore, discrimination of single nucleotide polymorphism is essential to detect cancer mutations. This study introduces a method with high sensitivity and selectivity of real-time PCR using peptide nucleic acid (PNA) and RNase H II to detect KRAS single nucleotide polymorphism. This method was developed via the fusion of the existing PNA clamping PCR technique and the RNase H-dependent PCR technique. A synergistic effect was realized by mitigating the shortcomings of each method. Our method had a detection limit of 1 aM and selectivity of 0.01%. This study demonstrated completed validation tests with DNA-spiked plasma sample analysis, cell culture, and analysis of blood samples collected from patients with cancer. Furthermore, we demonstrated the applicability of this method for breath biopsy.
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The global spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) proved to be a challenge for public health. The high demand of medical masks worldwide during the pandemic has led to a critical situation for decision-makers regarding high-quality mask supply. For this period, the World Health Organization has suggested the use of non-medical face masks (also known as ‘community’ masks) in public places to reduce the airborne spread of SARS-CoV-2. In this study, the filtration efficiency of various fabrics widely used in community masks was determined based on two main mask filtering properties: filtration efficiency (FE) and pressure drop (ΔP) according to the recommendations of the CEN Workshop Agreement (CWA) 17553:2020. The combination of FE and ΔP parameters must be considered in order to select suitable materials for public masks. The filtration efficiencies for various fabrics ranged from 6 to 100%. It was found that the composite materials have the highest FE equivalent to the requirements of a medical mask (FE > 95%), that is confirmed by high-quality parameters 16–30 kPa–1. The study found that fabrics of natural fibres (100% cotton) have a higher FE with Ag coating (18–40% before and 29–40% after coating) in the 0.54–1.50 μm particle size range.
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Face mask use by the general public for limiting the spread of the COVID-19 pandemic is controversial, though increasingly recommended, and the potential of this intervention is not well understood. We develop a compartmental model for assessing the community-wide impact of mask use by the general, asymptomatic public, a portion of which may be asymptomatically infectious. Model simulations, using data relevant to COVID-19 dynamics in the US states of New York and Washington, suggest that broad adoption of even relatively ineffective face masks may meaningfully reduce community transmission of COVID-19 and decrease peak hospitalizations and deaths. Moreover, mask use decreases the effective transmission rate in nearly linear proportion to the product of mask effectiveness (as a fraction of potentially infectious contacts blocked) and coverage rate (as a fraction of the general population), while the impact on epidemiologic outcomes (death, hospitalizations) is highly nonlinear, indicating masks could synergize with other non-pharmaceutical measures. Notably, masks are found to be useful with respect to both preventing illness in healthy persons and preventing asymptomatic transmission. Hypothetical mask adoption scenarios, for Washington and New York state, suggest that immediate near universal (80%) adoption of moderately (50%) effective masks could prevent on the order of 17–45% of projected deaths over two months in New York, while decreasing the peak daily death rate by 34–58%, absent other changes in epidemic dynamics. Even very weak masks (20% effective) can still be useful if the underlying transmission rate is relatively low or decreasing: In Washington, where baseline transmission is much less intense, 80% adoption of such masks could reduce mortality by 24–65% (and peak deaths 15–69%), compared to 2–9% mortality reduction in New York (peak death reduction 9–18%). Our results suggest use of face masks by the general public is potentially of high value in curtailing community transmission and the burden of the pandemic. The community-wide benefits are likely to be greatest when face masks are used in conjunction with other non-pharmaceutical practices (such as social-distancing), and when adoption is nearly universal (nation-wide) and compliance is high.
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The detection and quantification of enteric RNA viruses is based on isolation of viral RNA from the sample followed by quantitative reverse transcription polymerase chain reaction (RT-qPCR). To control the whole process of analysis and in order to guarantee the validity and reliability of results, process control viruses (PCV) are used. The present article describes the process of preparation and use of such PCV– MS2 phage-like particles (MS2 PLP) – in RT-qPCR detection and quantification of enteric RNA viruses. The MS2 PLP were derived from bacteriophage MS2 carrying a unique and specific de novo-constructed RNA target sequence originating from the DNA of two extinct species. The amount of prepared MS2 particles was quantified using four independent methods – UV spectrophotometry, fluorimetry, transmission electron microscopy and a specifically developed duplex RT-qPCR. To evaluate the usefulness of MS2 PLP in routine diagnostics different matrices known to harbor enteric RNA viruses (swab samples, liver tissue, serum, feces, and vegetables) were artificially contaminated with specific amounts of MS2 PLP. The extraction efficiencies were calculated for each individual matrix. The prepared particles fulfill all requirements for PCV – they are very stable, non-infectious, and are genetically distinct from the target RNA viruses. Due to these properties they represent a good morphological and physiochemical model. The use of MS2 PLP as a PCV in detection and quantification of enteric RNA viruses was evaluated in different types of matrices.
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Staphylococcus aureus is an aggressive pathogen and a model organism to study cell division in sequential orthogonal planes in spherical bacteria. However, the small size of staphylococcal cells has impaired analysis of changes in morphology during the cell cycle. Here we use super-resolution microscopy and determine that S. aureus cells are not spherical throughout the cell cycle, but elongate during specific time windows, through peptidoglycan synthesis and remodelling. Both peptidoglycan hydrolysis and turgor pressure are required during division for reshaping the flat division septum into a curved surface. In this process, the septum generates less than one hemisphere of each daughter cell, a trait we show is common to other cocci. Therefore, cell surface scars of previous divisions do not divide the cells in quadrants, generating asymmetry in the daughter cells. Our results introduce a need to reassess the models for division plane selection in cocci.
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The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10 μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, respectively, the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton–silk, cotton–chiffon, cotton–flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of “fit” and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.
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Background Face mask usage by the healthy population in the community to reduce risk of transmission of respiratory viruses remains controversial. We assessed the effect of community-wide mask usage to control coronavirus disease 2019 (COVID-19) in Hong Kong Special Administrative Region (HKSAR). Methods Patients presenting with respiratory symptoms at outpatient clinics or hospital wards were screened for COVID-19 per protocol. Epidemiological analysis was performed for confirmed cases, especially persons acquiring COVID-19 during mask-off and mask-on settings. The incidence of COVID-19 per-million-population in HKSAR with community-wide masking was compared to that of non-mask-wearing countries which are comparable with HKSAR in terms of population density, healthcare system, BCG vaccination and social distancing measures but not community-wide masking. Compliance of face mask usage in the HKSAR community was monitored. Findings Within first 100 days (31 December 2019 to 8 April 2020), 961 COVID-19 patients were diagnosed in HKSAR. The COVID-19 incidence in HKSAR (129.0 per-million-population) was significantly lower (p<0.001) than that of Spain (2983.2), Italy (2250.8), Germany (1241.5), France (1151.6), U.S. (1102.8), U.K. (831.5), Singapore (259.8), and South Korea (200.5). The compliance of face mask usage by HKSAR general public was 96.6% (range: 95.7% to 97.2%). We observed 11 COVID-19 clusters in recreational ‘mask-off’ settings compared to only 3 in workplace ‘mask-on’ settings (p = 0.036 by Chi square test of goodness-of-fit). Conclusion Community-wide mask wearing may contribute to the control of COVID-19 by reducing virus shedding in saliva and respiratory droplets from individuals with subclinical or mild COVID-19.
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Novel coronavirus (SARS-CoV-2) is found to cause a large outbreak started from Wuhan since December 2019 in China and SARS-CoV-2 infections have been reported with epidemiological linkage to China in 25 countries until now. We isolated SARS-CoV-2 from the oropharyngeal sample obtained from the patient with the first laboratory-confirmed SARS-CoV-2 infection in Korea. Cytopathic effects of SARS-CoV-2 in the Vero cell cultures were confluent 3 days after the first blind passage of the sample. Coronavirus was confirmed with spherical particle having a fringe reminiscent of crown on transmission electron microscopy. Phylogenetic analyses of whole genome sequences showed that it clustered with other SARS-CoV-2 reported from Wuhan.