Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?

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DOI: 10.1017/dmp.2013.43 · Source: PubMed
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Abstract
This study examined homemade masks as an alternative to commercial face masks. Several household materials were evaluated for the capacity to block bacterial and viral aerosols. Twenty-one healthy volunteers made their own face masks from cotton t-shirts; the masks were then tested for fit. The number of microorganisms isolated from coughs of healthy volunteers wearing their homemade mask, a surgical mask, or no mask was compared using several air-sampling techniques. The median-fit factor of the homemade masks was one-half that of the surgical masks. Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the homemade mask. Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection. (Disaster Med Public Health Preparedness. 2013;0:1-6).
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TestingtheEfficacyofHomemadeMasks:WouldTheyProtectinan
InfluenzaPandemic?
AnnaDavies,KatyAnneThompson,KarthikaGiri,GeorgeKafatos,JimmyWalkerandAllanBennett
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DOI:10.1017/dmp.2013.43,Publishedonline:22May2013
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ORIGINAL RESEARCH
Testing the Efficacy of Homemade Masks: Would
They Protect in an Influenza Pandemic?
Anna Davies, BSc, Katy-Anne Thompson, BSc, Karthika Giri, BSc, George Kafatos, MSc,
Jimmy Walker, PhD, and Allan Bennett, MSc
ABSTRACT
Objective: This study examined homemade masks as an alternative to commercial face masks.
Methods: Several household materials were evaluated for the capacity to block bacterial and viral aerosols.
Twenty-one healthy volunteers made their own face masks from cotton t-shirts; the masks were then tested
for fit. The number of microorganisms isolated from coughs of healthy volunteers wearing their homemade
mask, a surgical mask, or no mask was compared using several air-sampling techniques.
Results: The median-fit factor of the homemade masks was one-half that of the surgical masks. Both
masks significantly reduced the number of microorganisms expelled by volunteers, although the
surgical mask was 3 times more effective in blocking transmission than the homemade mask.
Conclusion: Our findings suggest that a homemade mask should only be considered as a last resort to
prevent droplet transmission from infected individuals, but it would be better than no protection.
(Disaster Med Public Health Preparedness. 2013;0:1–6)
Key Words: homemade facemasks, respirators, airborne transmission, microbial dispersion, pandemic
prevention
Wearing a face mask in public areas may
impede the spread of an infectious disease
by preventing both the inhalation of
infectious droplets and their subsequent exhalation
and dissemination. In the event of a pandemic
involving an airborne-transmissible agent, the general
public will have limited access to the type of high-
level respiratory protection worn by health care
workers, such as N95 respirators. Images of members
of the public wearing surgical masks were often used
to illustrate the 2009 H1N1 flu pandemic. However,
the evidence of proportionate benefit from widespread
use of face masks is unclear.
A recent prospective cluster-randomized trial compar-
ing surgical masks and non-fit-tested P2 masks (filters
at least 94% of airborne particles) with no mask use in
the prevention of influenza-like illness. The findings
of the study found that adherence to mask use
significantly reduced (95% CI, 0.09-0.77; P5.015)
the risk for infection associated with influenza-like
illness, but that less than 50% of participants wore
masks most of the time.
1
Facemasks may prevent
contamination of the work space during the outbreak
of influenza or other droplet-spread communicable
disease by reducing aerosol transmission. They may
also be used to reduce the risk of body fluids, including
blood, secretions, and excretions, from reaching the
wearer’s mouth and nose.
To date, studies on the efficacy and reliability of face
masks have concentrated on their use by health care
workers. Although health care workers are likely to
be one of the highest risk groups in terms of exposure,
they are also more likely to be trained in the use of
masks and fit tested than the general public. Should
the supply of standard commercial face masks not
meet demand, it would be useful to know whether
improvised masks could provide any protection to
others from those who are infected.
METHODS AND MATERIALS
In this study, common household materials(see
Table 1) were challenged with high concentrations
of bacterial and viral aerosols to assess their filtration
efficiencies. Surgical masks have been considered the
type of mask most likely to be used by the general
public, and these were used as a control. The pressure
drop across each of the materials was measured to
determine the comfort and fit between face and mask
that would be needed to make the material useable in
mask form. We devised a protocol for constructing a
‘‘homemade’’ mask, based on the design of a surgical
mask, and volunteers were invited to make their own
masks. These were then quantitatively fit tested. To
determine the effect of homemade and surgical masks
in preventing the dispersal of droplets and aerosol
particles produced by the wearer, the total bacterial
Disaster Medicine and Public Health Preparedness 1
Copyright &2013 Society for Disaster Medicine and Public Health, Inc. DOI: 10.1017/dmp.2013.43
count was measured when the volunteers coughed wearing
their homemade mask, a surgical mask, and no mask.
Testing the Filtration Efficiency
A range of common household materials were tested, together
with the material from a surgical mask (Mo
¨lnlycke Health Care
Barrier face mask 4239, EN14683 class I), for comparison.
Circular cutouts of the tested materials were placed without
tension in airtight casings, creating a ‘‘filter’’ in which the
material provided the only barrier to the transport of the aerosol.
A Henderson apparatus allows closed-circuit generation of
microbial aerosols from a Collison nebulizer at a controlled
relative humidity. This instrument was used to deliver the
challenge aerosol across each material at 30 L/min using
the method of Wilkes et al,
2
which is about 3 to 6 times per
minute the ventilation of a human at rest or doing light work,
but is less than 0.1 the flow of an average cough.
Downstream air was sampled simultaneously for 1 minute into
10 ml of phosphate buffer manucol antifoam using 2 all-glass
impingers. One impinger sampled the microorganisms that
had penetrated through the material filter, while the other
sampled the control (no filter). The collecting fluid was
removed from the impingers and assayed for microorganisms.
This test was performed 9 times for each material. The
filtration efficiency (FE) of the fabric was calculated using the
following formula (cfu indicate colony-forming units):
FE ¼Upstream cfu Downstream cfu 100
Upstream cfu
The pressure drop across the fabric was measured using a
manometer (P200UL, Digitron), with sensors placed on
either side of the filter casing, while it was challenged with a
clean aerosol at the same flow rate.
Microorganisms
Two microorganisms were used to simulate particle challenge:
Bacillus atrophaeus is a rod-shaped spore-forming bacterium
(0.95-1.25 mm) known to survive the stresses caused by
aerosolization.
3
The suspension was prepared from batches
previously prepared by the Health Protection Agency, Centre
for Emergency Preparedness and Response Production Division.
4
Each material was challenged with approximately 10
7
cfu
B atrophaeus.
Bacteriophage MS2 (MCIMB10108) is a nonenveloped
single-stranded RNA coliphage, 23 nm in diameter, known
to survive the stresses of aerosolization.
5
Each material was
challenged with approximately 10
9
plaque-forming units
(pfu) of bacteriophage MS2.
The two test organisms can be compared in size to influenza
virus, which is pleomorphic and ranges from 60 to 100 nm;
Yersinia pestis, which is 0.75 mm; Banthracis,which is 1 to
1.3 mm; Francisella tularensis, which is 0.2 mm; and Mycobacterium
tuberculosis, which is 0.2 to 0.5 mm.
6
Bacteriophage MS2 and
B atrophaeus were chosen as the test organisms to represent
influenza virus. This decision was made not only because of the
lower risks of associated infection but also because the work
would be technically easier to carry out using an Advisory
Committee on Dangerous Pathogens (ACDP) class 1 organism
versus an ACDP class 2 organism influenza.
Making the Face Mask
For this study, 21 healthy volunteers were recruited, 12 men
and 9 women. The participants were aged between 20 and
44 years; the majority was in the 20- to 30-year age range.
Each volunteer made a homemade face mask following a
protocol devised by the authors. All face masks were made
with 100% cotton t-shirt fabric using sewing machines to
speed construction. A surgical mask (Mo
¨lnlycke Health Care
TABLE 1
Filtration Efficiency and Pressure Drop Across Materials Tested with Aerosols of Bacillus atrophaeus and Bacteriophage
MS2 (30 L/min)
a
Material
B atrophaeus Bacteriophage MS2 Pressure Drop Across Fabric
Mean % Filtration Efficiency SD Mean % Filtration Efficiency SD Mean SD
100% cotton T-shirt 69.42 (70.66) 10.53 (6.83) 50.85 16.81 4.29 (5.13) 0.07 (0.57)
Scarf 62.30 4.44 48.87 19.77 4.36 0.19
Tea towel 83.24 (96.71) 7.81 (8.73) 72.46 22.60 7.23 (12.10) 0.96 (0.17)
Pillowcase 61.28 (62.38) 4.91 (8.73) 57.13 10.55 3.88 (5.50) 0.03 (0.26)
Antimicrobial Pillowcase 65.62 7.64 68.90 7.44 6.11 0.35
Surgical mask 96.35 0.68 89.52 2.65 5.23 0.15
Vacuum cleaner bag 94.35 0.74 85.95 1.55 10.18 0.32
Cotton mix 74.60 11.17 70.24 0.08 6.18 0.48
Linen 60.00 11.18 61.67 2.41 4.50 0.19
Silk 58.00 2.75 54.32 29.49 4.57 0.31
a
Numbers in parentheses refer to the results from 2 layers of fabric.
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness2
Barrier face mask 4239, EN14683 class I) was used as
a control. Also, all volunteers completed a questionnaire
indicating their opinions of mask wearing.
Determining the Fit Factor of the Mask
A commercial fit test system (TSI PortaCount Plus Respirator
Fit Tester and N95- Companion Module model 8095) was
used to measure respirator fit by comparing the concentration
of microscopic particles outside the respirator with the
concentration of particles that have leaked into the respirator.
The ratio of these 2 concentrations is known as the fit factor.
To conduct the fit test, the apparatus was set up and operated
according to the manufacturer’s instructions.
Volunteers were instructed to fit their surgical and homemade
face masks with no help or guidance from the operator; to
ensure that the mask was comfortable for 2 minutes; the
participants were given time to purge any particles trapped
inside the mask. The fit test was then conducted with
volunteers performing the following consecutive exercises,
each lasting 96 seconds: (1) normal breathing, (2) deep
breathing,
7
(3) head moving side to side, (4) head moving up
and down, (5) talking aloud (reading a prepared paragraph),
(6) bending at the waist as if touching their toes, and
(7) normal breathing.
Determining the Effect of Masks in Preventing the
Dispersal of Droplets and Aerosol
An enclosed 0.5-m
3
mobile sampling chamber, or cough box,
which was constructed for the purpose of sampling aerosols and
droplets from healthy volunteers (PFI Systems Ltd, Milton
Keynes), was placed in a 22.5-m
3
high-frequency particulate
air-filtered environmental room. Four settle plates were placed
in the cough box to sample for droplets, together with a 6-stage
Andersen sampler to sample and separate small particles.
8
A Casella slit-air sampler
9
was also attached to the cough box.
Tryptose soya agar was used as the culture medium. Volunteers
wearing protective clothing (Tyvek suits) coughed twice into
the box, and the air inside was sampled for 5 minutes. Each
volunteer was sampled 3 times: wearing the homemade mask,
the surgical mask, and no mask. The air within the cough box
was high-frequency particulate air filtered for 5 minutes
between each sample to prevent cross-contamination between
samples. The plates were incubated for a minimum of 48 hours
at 378C before counting.
Statistical Analysis
To evaluate the face mask fit, the median and interquartile
range were calculated for each exercise and face mask for
the 21 individuals. Wilcoxon sign rank tests were used to
compare the masks. The same approach was used to
determine differences between the different mask types
and their efficacy in preventing dissemination of droplets
and particles
RESULTS
Filtration Efficacy
All the materials tested showed some capability to block
the microbial aerosol challenges. In general, the filtration
efficiency for bacteriophage MS2 was 10% lower than for
B atrophaeus (Table 1). The surgical mask had the highest
filtration efficiency when challenged with bacteriophage
MS2, followed by the vacuum cleaner bag, but the bag’s
stiffness and thickness created a high pressure drop across
the material, rendering it unsuitable for a face mask. Simi-
larly, the tea towel, which is a strong fabric with a thick
weave, showed relatively high filtration efficiency with both
B atrophaeus and bacteriophage MS2, but a high pressure
drop was also measured.
The surgical mask (control) showed the highest filtration
efficiency with B atrophaeus. Also, as expected, its measured
low pressure drop showed it to be the most suitable material
among those tested for use as a face mask. The pillowcase and
the 100% cotton t-shirt were found to be the most suitable
household materials for an improvised face mask. The slightly
stretchy quality of the t-shirt made it the more preferable
choice for a face mask as it was considered likely to provide a
better fit.
Although doubling the layers of fabric did significantly
increase the pressure drop measured across all 3 materials
(P,.01 using Wilcoxon sign rank test), only the 2 layers of
tea towel material demonstrated a significant increase in
filtration efficiency that was marginally greater than that of
the face mask.
In the questionnaire on mask use during a pandemic,
6 participants said they would wear a mask some of the time,
6 said they would never wear a mask, and 9 either did not
know or were undecided. None of the participants said that
they would wear a mask all of the time. With 1 exception, all
participants reported that their face mask was comfortable.
However, the length of time each participant kept their mask
on during testing was minimal (15 min), and with long-term
wear, comfort might decrease.
Facemask Fit Testing
A Wilcoxon sign rank test showed a significant difference
between the homemade and surgical mask for each exercise
and in total (all tests showed P,.001). The median and
interquartile range for each mask and exercise are given in
Table 2.
Prevention of Droplet and Particle Dissemination
When Coughing
Results from the cough box experiments showed that both
the surgical mask and the homemade mask reduced the total
number of microorganisms expelled when coughing (P,.001
and P5.004, respectively; see Table 3).
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness 3
On analyzing the effect of mask wearing in reducing the
number of microorganisms isolated from the Anderson air
sampler (Table 4), the surgical mask was found to be
generally more effective in reducing the number of micro-
organisms expelled than the homemade mask, particularly at
the lowest particle sizes. The number of microorganisms
isolated from the coughs of healthy volunteers was generally
low, although this varied according to the individual sampled
(Table 3). It is possible, therefore, that the sampling
limitations negatively affected the statistical analysis.
Pearson x
2
tests comparing the proportion of particles greater
than 4.7 mm in diameter and particles less than 4.7mmin
diameter found that the homemade mask did not significantly
reduce the number of particles emitted (P5.106). In contrast,
the surgical mask did have a significant effect (P,.001).
DISCUSSION
Facemasks reduce aerosol exposure by a combination of the
filtering action of the fabric and the seal between the mask
and the face. The filtration efficiency of the fabric depends
on a variety of factors: the structure and composition of the
fabric, and the size, velocity, shape, and physical properties of
the particles to which it is exposed.
10
Although any material
may provide a physical barrier to an infection, if as a mask it
does not fit well around the nose and mouth, or the material
freely allows infectious aerosols to pass through it, then it will
be of no benefit.
The test organisms in this study can be used to estimate
the efficacy of these masks against influenza virus because
essentially any aerosolized particle will behave predominately
in the air as a result of its physical characteristics rather than
its biological properties (ie, influenza virus particles will travel
in the air in the same manner as particles of an equivalent
size). Therefore, as we have tested a viral pathogen smaller
than influenza and a bacterial pathogen larger than influenza,
we have tested the face masks with a suitable challenge across
the size range of influenza virus particles. Furthermore, the
data from this study could also be applied to other organisms
within this size range that are potentially transmitted via the
aerosol route.
Quantitative fit testing can only estimate the combined
effects of filtration efficiency and goodness of fit. Although
sensitive to particles with diameters as small as 0.02 mm, it is
not sensitive to variations in particle size, shape, composition,
or refractive index. As a result, this method of fit testing
does not allow the distinction between true bioaerosols and
droplet contamination.
A study conducted in the Netherlands using a commercial
fit-test system (Portacount Plus Respirator Fit Tester) on
volunteers wearing both improvised masks made from tea
cloths and surgical masks over a 3-hour period found results
similar to those found in this study.
11
The authors
demonstrated a median protection factor of between 2.2
and 2.5 for various activities when wearing a mask with a tea
TABLE 2
Median and Interquartile Range Results from
Respirator Fit Testing of Homemade and Surgical
Masks
Median Interquartile Range
Condition Homemade Mask Surgical Mask
Normal breathing 2.0 (2.0, 2.5) 6.0 (2.5, 9.0)
Heavy breathing 2.0 (2.0, 3.0) 7.0 (2.5, 13.5)
Head moving side to side 2.0 (1.0, 2.0) 5.0 (3.0, 7.0)
Head moving up and down 2.0 (1.5, 2.0) 5.0 (3.0, 7.0)
Bending over 1.0 (1.0, 2.0) 3.0 (2.0, 9.0)
Talking 2.0 (1.0, 2.0) 6.0 (3.0, 12.0)
Normal 2.0 (1.0, 2.0) 5.0 (2.0, 8.5)
All data 2.0 (1.0, 2.0) 5.0 (3.0, 9.0)
TABLE 3
Median Colony-Forming Units by Sampling Method
Isolated From Volunteers Coughing When Wearing a
Surgical Mask, a Homemade Mask, and No Mask
Median Interquartile Range
Sampling Method No Mask Homemade Mask P
Air 6.0 (1.0, 26.5) 1.0 (0.5, 6.5) .007
Settle plates 1.0 (0.0, 3.0) 1.0 (0.0, 2.0) .224
Total 2.0 (0.0, 12.3) 1.0 (0.0, 3.0) .004
Median Interquartile Range
Sampling Method No Mask Surgical Mask P
Air 6.0 (1.0, 26.5) 1.0 (0.5, 3.0) .002
Settle plates 1.0 (0.0, 3.0) 0.0 (0.0, 0.0) .002
Total 2.0 (0.0, 12.3) 0.0 (0.0, 1.0) ,.001
TABLE 4
Total Colony-Forming Units Isolated by Particle Size
From 21 Volunteers Coughing When Wearing a
Surgical Mask, Homemade Mask, and No Mask
Particle Diameter, mm No Mask Homemade Mask Surgical Mask
.7935
4.7-7 18 7 7
3.3-4.7 5 4 4
2.1-3.3 47 7 5
1.1-2.1 100 16 6
0.65-1.1 21 6 3
Total 200 43 30
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness4
towel filter and protection factors of between 4.1 and 5.3
for the surgical mask. It was interesting that the study also
found that median protection factors increased over the
3-hour period for those wearing the homemade masks,
decreased for those wearing filtering face piece (FFP2) masks
that lower the wearer’s exposure to airborne particles by a
factor of 10, and showed no consistent pattern for those
wearing a surgical mask.
11
The materials used in this published study were fresh and
previously unworn. It is likely that materials conditioned
with water vapor, to create a fabric similar to that which has
been worn for a couple of hours, would show very different
filtration efficiencies and pressure drops. In contrast, a study
of breathing system filters found a greater breakthrough of
bacteriophage MS2 on filters that had been preconditioned.
Although the droplet sizes for both virus and bacteria were
the same and affected the filter media in a similar manner, it
was suggested that the viruses, after contact with the moisture
on the filter, were released from their droplet containment,
and driven onward by the flow of gas.
12
The average concentration of Streptococcus organisms in
saliva has been estimated to be 6.7 310
7
cfu/mL,
13
which
is higher than that of influenza viruses in inoculated
volunteers.
14
Therefore, the number of oral microorganisms
isolated may well provide an indication of the concentration
of influenza being shed. Results from the cough box
demonstrated that surgical masks have a significant effect in
preventing the dispersal of large droplets and some smaller
particles when healthy volunteers coughed. The homemade
mask also prevented the release of some particles, although
not at the same level as the surgical mask. The numbers
of microorganisms isolated from the coughs of healthy
volunteers was in general very low, and it is likely that had
we used volunteers with respiratory infections, the homemade
mask may have shown a more significant effect in preventing
the release of droplets.
It was observed during this study that there was greater
variation among volunteers in their method of fitting the
surgical mask. The need to tie the straps at the back of the
head meant that the surgical mask was fit in a variety of ways.
In contrast, the face mask had looped elastic straps that were
easier for the volunteer to fit.
Comfort should be an important factor in the material used to
make a homemade mask. The pressure drop across a mask is a
useful measure both of resistance to breathing and the
potential for bypass of air around the filter seal. If respiratory
protection is not capable of accommodating the breathing
demands of the wearer, then the device will impose an extra
breathing load on the wearer, which is especially impractic-
able for people with breathing difficulties. Furthermore,
the extra breathing load may induce leakage owing to the
increased negative pressure in the face mask.
15
In practice, people will not wear an uncomfortable mask for
a long period; even if they do, it is unlikely that they will
wear the mask properly. During the outbreak of severe acute
respiratory syndrome, an account of a flight from Bangkok,
Thailand, to Manchester, England. described mask wearers
removing their mask to cough, sneeze, and wipe their nose
(not necessarily into a handkerchief) and to sort through the
communal bread basket.
16
For those who wear a mask for
necessity, such as health care workers, regular training and fit
testing must be emphasized. Whereas, for those who choose
to wear a homemade mask, the requirements of cleaning and
changing the mask should be highlighted. Most importantly,
the lower protective capabilities of a homemade mask should
be emphasized so that unnecessary risks are not taken.
CONCLUSION
A protective mask may reduce the likelihood of infection, but
it will not eliminate the risk, particularly when a disease has
more than 1 route of transmission. Thus any mask, no matter
how efficient at filtration or how good the seal, will have
minimal effect if it is not used in conjunction with other
preventative measures, such as isolation of infected cases,
immunization, good respiratory etiquette, and regular hand
hygiene. An improvised face mask should be viewed as the
last possible alternative if a supply of commercial face masks is
not available, irrespective of the disease against which it may
be required for protection. Improvised homemade face masks
may be used to help protect those who could potentially, for
example, be at occupational risk from close or frequent
contact with symptomatic patients. However, these masks
would provide the wearers little protection from microorgan-
isms from others persons who are infected with respiratory
diseases. As a result, we would not recommend the use of
homemade face masks as a method of reducing transmission
of infection from aerosols.
About the Authors
Public Health England (HPA), Porton Down Salisbury (Dr Walker, Miss Thompson,
Davies and Giri, and Mr Bennett); PHE, Colindale, London (Mr Kafatos),
United Kingdom.
Address correspondence and reprint requests to Jimmy Walker, PhD, PHE, Porton
Down, Salisbury, SP4 0JG UK (e-mail: jimmy.walker@phe.gov.uk).
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Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness6

Supplementary resources

  • ... Even masks routinely used by medical staff in hospitals and doctor's offices have almost no significant filtering effect on the droplet sizes typically produced when breathing, speaking, singing and coughing. The results are therefore in good agreement with the results from (Leung et al., 2020and Davies et al., 2013and Kwok et al., 2015. But why has wearing these masks been shown to provide effective protection against infection with the virus in the SARS epidemic, as shown in , Lo et al., 2005and Seto et al., 2003? ...
    ... Some recent studies show that even the simple materials we have tested have some filtering ability (Davies et al., 2013;Drewnick, 2020;Konda et al., 2020 andvan der Sande et al., 2008), We do not question these results, although the pressure drops in one study is anomalously low (see supporting information in Konda et al., 2020), but we state explicitly that a material that does not have an adequate filtering ability equivalent to an FFP2/N95/KN95 mask cannot be recommended as a filter material for self-protection against droplet infection. Statistically speaking, every loss of performance leads to an increase in the number of infected people and thus to an increase in the number of death. ...
    Article
    Full-text available
    Many governments have instructed the population to wear simple mouth-and-nose covers or surgical face masks to protect themselves from droplet infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in public. However, the basic protection mechanisms and benefits of these masks remain controversial. Therefore, the aim of this work is to show from a fluid physics point of view under which circumstances these masks can protect against droplet infection. First of all, we show that the masks protect people in the surrounding area quite well, since the flow resistance of the face masks effectively prevents the spread of exhaled air, e.g. when breathing, speaking, singing, coughing and sneezing. Secondly, we provide visual evidence that typical household materials used by the population to make masks do not provide highly efficient protection against respirable particles and droplets with a diameter of 0.3–2 μm as they pass through the materials largely unfiltered. According to our tests, only vacuum cleaner bags with fine dust filters show a comparable or even better filtering effect than commercial particle filtering FFP2/N95/KN95 half masks. Thirdly, we show that even simple mouth-and-nose covers made of good filter material cannot reliably protect against droplet infection in contaminated ambient air, since most of the air flows through gaps at the edge of the masks. Only a close-fitting, particle-filtering respirator without an outlet valve offers good self-protection and protection against droplet infection. Nevertheless, wearing simple homemade or surgical face masks in public is highly recommended if no particle filtrating respiratory mask is available. Firstly, because they protect against habitual contact of the face with the hands and thus serve as self-protection against contact infection. Secondly, because the flow resistance of the masks ensures that the air stays close to the head when breathing, speaking, singing, coughing and sneezing, thus protecting other people if they have sufficient distance from each other. However, if the distance rules cannot be observed and the risk of inhalation-based infection becomes high because many people in the vicinity are infectious and the air exchange rate is small, improved filtration efficiency masks are needed, to take full advantage of the three fundamental protective mechanisms these masks provide.
  • ... Typical definitions of droplet size use a minimum of 5 µm-10 µm (61). Generally available household materials had between a 58% and 94% filtration rate for 1 µm bacteria particles whereas surgical masks filtered 96% of those particles (80). A tea cloth mask was found to filter 60% of particles between 0.02 µm to 1 µm, where surgical masks filtered 75% (81). ...
    ... A tea cloth mask was found to filter 60% of particles between 0.02 µm to 1 µm, where surgical masks filtered 75% (81). Simulation studies generally use a 30 L/min or higher challenge aerosol, which is around about 3 to 6 times per minute the ventilation of a human at rest or doing light work (80). As a result, simulation studies may underestimate the efficacy of the use of unfitted masks in the community in practice. ...
    Preprint
    The science around the use of masks by the general public to impede COVID-19 transmission is advancing rapidly. Policymakers need guidance on how masks should be used by the general population to combat the COVID-19 pandemic. In this narrative review, we develop an analytical framework to examine mask usage, considering and synthesizing the relevant literature to inform multiple areas: population impact; transmission characteristics; source control; PPE; sociological considerations; and implementation considerations. A primary route of transmission of COVID-19 is via respiratory droplets, and is known to be transmissible from presymptomatic and asymptomatic individuals. Reducing disease spread requires two things: first, limit contacts of infected individuals via physical distancing and other measures, and second, reduce the transmission probability per contact. The preponderance of evidence indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets in both laboratory and clinical contexts. Public mask wearing is most effective at reducing spread of the virus when compliance is high. The decreased transmissibility could substantially reduce the death toll and economic impact while the cost of the intervention is low. Given the current shortages of medical masks we recommend the adoption of public cloth mask wearing, as an effective form of source control, in conjunction with existing hygiene, distancing, and contact tracing strategies. Because many respiratory droplets become smaller due to evaporation, we recommend increasing focus on a previously overlooked aspect of mask usage: mask-wearing by infectious people ("source control") with benefits at the population-level, rather than mask-wearing by susceptible people, such as health-care workers, with focus on individual outcomes. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.
  • ... The effects of masking on the epidemic of COVID-19 in the USA was simulated using the filtering efficacy of masks on influenza. 23, 24 The influence of public intervention on COVID-19 Rt is one of the most widely used metrics for assessing transmission rate of infectious diseases, 8,25 and linked to the incidence decay with exponential adjustment model (known as IDEA) and Farr's law. 32 However, Rt is difficult to estimate. ...
  • ... This would be better than nothing, as masks are scientifically proven as effective in preventing droplet spreading in hospital settings [18] and surgical masks can be potentially more effective in stopping COVID-19 spread via the droplets similar to influenza [19]. Homemade masks have also been proven to be useful and recommended in the literature, though offering less protection than surgical quality masks [20,21]. Masking not only helps to stop the spread of COVID-19, but may also reduce the spread of other diseases so that valuable medical resources can be conserved. ...
    Article
    Full-text available
    With the rapid development of the COVID-19 pandemic, countries are trying to cope with increasing medical demands, and, at the same time, to reduce the increase of infected numbers by implementing a number of public health measures, namely non-pharmaceutical interventions (NPIs). These public health measures can include social distancing, frequent handwashing, and personal protective equipment (PPE) at the personal level; at the community and the government level, these measures can range from canceling activities, avoiding mass gatherings, closing facilities, and, at the extreme, enacting national or provincial lockdowns. Rather than completely stopping the infectious disease, the major purpose of these NPIs in facing an emerging infectious disease is to reduce the contact rate within the population, and reduce the spread of the virus until the time a vaccine or reliable medications become available. The idea is to avoid a surge of patients with severe symptoms beyond the capacity of the hospitals' medical resources, which would lead to more mortality and morbidity. While many countries have experienced steep curves in new cases, some, including Hong Kong, Vietnam, South Korea, New Zealand, and Taiwan, seem to have controlled or even eliminated the infection locally. From its first case of COVID-19 on the 21 January until the 12 May, Taiwan had 440 cases, including just 55 local infections, and seven deaths in total, representing 1.85 cases per 100,000 population and a 1.5% death rate (based on the Worldometer 2020 statistics of Taiwan's population of 23.8 million). This paper presents evidence that spread prevention involving mass masking and universal hygiene at the early stage of the COVID-19 pandemic resulted in a 50% decline of infectious respiratory diseases, based on historical data during the influenza season in Taiwan. These outcomes provide potential support for the effectiveness of widely implementing public health precaution measures in controlling COVID-19 without a lockdown policy.
  • ... The main issue tends to be air leakage, which can result in aerosolized pathogens being dispersed and suspended in the ambient environment for long periods of time after a coughing/sneezing event has occurred. A few studies have considered the filtration efficiency of homemade masks made with different types of fabric [48][49][50][51] , however there is no broad consensus regarding their effectiveness in minimizing disease transmission 52,53 . Nonetheless, the evidence suggests that masks and other face coverings are effective in stopping larger droplets, which although fewer in number compared to the smaller droplets and nuclei, constitute a large fraction of the total volume of the ejected respiratory fluid. ...
    Article
    Full-text available
    The use of face masks in public settings has been widely recommended by public health officials during the current COVID-19 pandemic. The masks help mitigate the risk of cross-infection via respiratory droplets, however, there are no specific guidelines on mask materials and designs that are most effective in minimizing droplet dispersal. While there have been prior studies on the performance of medical-grade masks, there is insufficient data on cloth-based coverings which are being used by a vast majority of the general public. We use qualitative visualizations of emulated coughs and sneezes to examine how material- and design-choices impact the extent to which droplet-laden respiratory jets are blocked. Loosely folded face masks and bandana-style coverings provide minimal stopping-capability for the smallest aerosolized respiratory droplets. Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks, proved to be the most effective in reducing droplet dispersal. These masks were able to curtail the speed and range of the respiratory jets significantly, albeit with some leakage through the mask material and from small gaps along the edges. Importantly, uncovered emulated coughs were able to travel noticeably farther than the currently recommended 6-foot distancing guideline. We outline the procedure for setting up simple visualization experiments using easily available materials, which may help healthcare professionals, medical researchers, and manufacturers in assessing the effectiveness of face masks and other personal protective equipment qualitatively.
  • Article
    Many healthcare systems have been forced to outsource simple mask production due to international shortages caused by the COVID-19 pandemic. Providence created simple masks using surgical wrap and submitted samples to an environmental lab for bacterial filtration efficiency testing. Bacterial filtration efficiency (BFE) rates ranged from 83.0 – 98.1% depending on specific material and ply, and particular filtration efficiency (PFE) rates ranged from 92.3-97.7%. Based on mask configuration, specific surgical wrap selected, and ply, the recommended filtration efficiency for isolation and surgical masks of 95% and 98%, respectively can be achieved. These alternative masks can allow for similar coverage and safety when hospital-grade isolation masks are in short supply.
  • Preprint
    Objective: To determine the effectiveness of non-medical grade washable masks or face coverings in controlling airborne dispersion from exhalation (both droplet and aerosol), and to aid in establishing public health strategies on the wearing of masks to reduce COVID-19 transmission. Design: This comparative effectiveness study using an exhalation simulator to conduct 94 experiment runs with combinations of 8 different fabrics, 5 mask designs, and airflows for both talking and coughing. Setting: Non-airtight fume hood and multiple laser scattering particle sensors. Participants: No human participants. Exposure: 10% NaCl nebulized solution delivered by an exhalation simulator through various masks and fabrics with exhalation airflows representative of "coughing" and "talking or singing." Main Outcomes and Measures: The primary outcome was reduction in aerosol dispersion velocity, quantity of particles, and change in dispersion direction. Measurements used in this study included peak expiratory flow (PEF), aerosol velocity, concentration area under curve (AUC), and two novel metrics of expiratory flow dispersion factor (EDF) and filtration efficiency indicator (FEI). Results: Three-way multivariate analysis of variance establishes that factors of fabric, mask design, and exhalation breath level have a statistically significant effect on changing direction, reducing velocity or concentration (Fabric: P = < .001, Wilks' Λ = .000; Mask design: P = < .001, Wilks' Λ = .000; Breath level: P = < .001, Wilks' Λ = .004). There were also statistically significant interaction effects between combinations of all primary factors. Conclusions and Relevance: The application of facial coverings or masks can significantly reduce the airborne dispersion of aerosolized particles from exhalation. The results show that wearing of non-medical grade washable masks or face coverings can help increase the effectiveness of non-pharmaceutical interventions (NPI) especially where infectious contaminants may exist in shared air spaces. However, the effectiveness varies greatly between the specific fabrics and mask designs used.
  • Preprint
    Full-text available
    The community lockdown measures implemented in the United States, during late March to end of May of 2020, resulted in a significant reduction in the community transmission of the COVID-19 pandemic throughout the country. However, a number of US states are currently experiencing an alarming post-lockdown resurgence of the pandemic, triggering the fear for a possible severe second wave of the pandemic in some US jurisdictions. We designed a mathematical model for addressing the key question of whether or not the universal use of face masks can halt or curtail such resurgence (and possibly avert a second wave, without having to undergo another cycle of major community lockdown) in the states of Arizona, Florida, New York and the entire US. The model was parametrized and fitted using cumulative mortality data from the four jurisdictions. Our study highlights the importance of early implementation of the community lockdown measures. In particular, a sizable reduction in the burden of the pandemic would have been recorded in each of the four jurisdictions if the community lockdown measures were implemented a week or two earlier. These reductions are greatly augmented if the early implementation of the lockdown measures is complemented with a public face masks use strategy. It is shown that the pandemic would have been almost completely suppressed from significantly taking off if the lockdown measures were implemented two weeks earlier, and if a sizable percentage of the residents of the four jurisdictions wore face masks during the respective lockdown periods. If the level of lifting of community lockdown is high (which entails allowing for greater community contacts and re-opening of businesses and social activities, in comparison to what was allowed during the community lockdown period), the states of Arizona and Florida will record a devastating second wave of the pandemic by the end of 2020, while the state of New York and the entire US will record milder second waves. If the level of lifting for the community lockdown was mild (i.e., only allowing very limited community contacts and business activities, in comparison to the lockdown period), only the state of Florida will experience a second wave. The severity of the projected second wave depends on the level of lifting of the community lockdown. For instance, the projected second wave for Arizona and Florida, associated with moderate and high level of lifting of lockdown, will be more severe than their respective first wave. For high level of lifting of lockdown measures, the increased use of face masks after the lockdown period greatly reduces the burden of the pandemic. In particular, for this high lifting scenario, none of the four jurisdictions will experience a second wave if half of their residents wear face masks consistently after their respective lockdown period). A testing strategy that increases the maximum detection rate of asymptomatic infected individuals (followed by contact tracing and self-isolation of the detected cases) greatly reduces the burden of the pandemic in all four jurisdictions, particularly if also combined with universal face mask use strategy. Universal use of face masks in public, with at least moderate level of compliance, could halt the post-lockdown resurgence of COVID-19, in addition to averting the potential for (or severity of) a second wave of the pandemic in each of the four jurisdictions.
  • Article
    The coronavirus disease (COVID-19) epidemic started in the Hubei province of China, but is rapidly spreading all over the world. Much of the information and literature have been centered on the adult population while a few reports pertaining to COVID-19 and neonates have been published so far. Actual guidelines are based on expert opinion and show significant differences among the official neonatal societies around the world. Recommendations for the care of neonates born to suspected or confirmed COVD-19 positive mothers in low-resource settings are very limited. This perspective aims to provide practical support for the planning of delivery, resuscitating, stabilizing, and providing postnatal care to an infant born to a mother with suspected or confirmed COVID-19 in low-resource settings where resources for managing emergency situations are limited.
  • Chapter
    The genus Bacillus comprises a heterogeneous group of chemoorganotrophic, aerobic, rod-shaped microorganisms. These include both mesophilic and thermophilic species as well as acidophiles and alkalophiles. One of their main characteristics is their ability to produce heat-resistant endospores.
  • Article
    The sedimentation behavior of influenza virus in dilute solutions of electrolyte was found to be quite variable. At times the virus activity appeared to sediment at a rate comparable with that of particles about 80 to 120 mmicro in diameter, at other times at a rate comparable with that of particles about 10 mmicro in diameter, and at still other times the bulk of the activity appeared to sediment at a rate comparable with that of the larger particles and the residual activity at a rate comparable with that of the smaller particles. However, in the presence of a sucrose density gradient, the virus activity was always found to sediment with a rate comparable to that of particles about 80 to 120 mmicro in diameter; hence it appeared that the variable sedimentation behavior in dilute electrolyte solution was due to convection or mechanical disturbances during centrifugation. About 30 per cent of the high molecular weight protein present in the allantoic fluid of chick embryos infected with the F 12 strain of influenza virus was found to consist of a component having a sedimentation constant of about 30 S, and hence a probable particle diameter of about 10 mmicro. The residual protein of high molecular weight was present in the form of a component having a sedimentation constant of about 600 S, and hence a probable particle diameter of about 70 mmicro. The proportion of the 30 S component in allantoic fluid of chick embryos infected with the PR8 strain of influenza virus was found to be considerably less. The 600 S and 30 S components of F 12 allantoic fluid were purified and separated by differential centrifugation. The purified preparations of the 600 S component were found to possess a specific virus activity from 100 to over 10,000 times that of the purified preparations of the 30 S component, the difference in activity apparently depending only on the degree of fractionation of the two components. The purified 30 S component was found to sediment normally in the presence of 12 per cent sucrose, whereas the small residual virus activity of such preparations was found to sediment in the presence of a sucrose density gradient with a rate comparable to that of much heavier particles. It is concluded that influenza virus activity is not associated with material having a particle diameter of about 10 mmicro, but is associated solely with material having a sedimentation constant of about 600 S and hence a probable particle diameter of about 70 mmicro.
  • Article
    Full-text available
    Many countries are stockpiling face masks for use as a nonpharmaceutical intervention to control virus transmission during an influenza pandemic. We conducted a prospective cluster-randomized trial comparing surgical masks, non–fit-tested P2 masks, and no masks in prevention of influenza-like illness (ILI) in households. Mask use adherence was self-reported. During the 2006 and 2007 winter seasons, 286 exposed adults from 143 households who had been exposed to a child with clinical respiratory illness were recruited. We found that adherence to mask use significantly reduced the risk for ILI-associated infection, but <50% of participants wore masks most of the time. We concluded that household use of face masks is associated with low adherence and is ineffective for controlling seasonal respiratory disease. However, during a severe pandemic when use of face masks might be greater, pandemic transmission in households could be reduced. Many countries are stockpiling face masks for use as nonpharmaceutical interventions to reduce viral transmission during an influenza pandemic. We conducted a prospective cluster-randomized trial comparing surgical masks, non–fit-tested P2 masks, and no masks in prevention of influenza-like illness (ILI) in households. During the 2006 and 2007 winter seasons, 286 exposed adults from 143 households who had been exposed to a child with clinical respiratory illness were recruited. Intent-to-treat analysis showed no significant difference in the relative risk of ILI in the mask use groups compared with the control group; however, <50% of those in the mask use groups reported wearing masks most of the time. Adherence to mask use was associated with a significantly reduced risk of ILI-associated infection. We concluded that household use of masks is associated with low adherence and is ineffective in controlling seasonal ILI. If adherence were greater, mask use might reduce transmission during a severe influenza pandemic.
  • Article
    During an epidemic of influenza B, 43 ambulatory children were prospectively followed to determine the quantitative shedding patterns of influenza B viral infection, because these have not been previously described. The spectrum of illness included 74% with a typical influenzalike illness, 7% with an afebrile infection of the upper respiratory tract, and 19% with croup. Mild myositis occurred in 21%. For the first three days of illness, ⩾93% of the children shed virus, and 74% shed on day 4. The average peak quantity of virus shed in the nasal wash was 4.0 log10 50% tissue culture infective doses/ml (range,1.5–6.0), which gradually declined over four days to 2.4 log10 50% tissue culture infective doses/ml. The quantities of virus shed correlated significantly with severity of illness and fever score, but not with sex, type of illness, or occurrence of myositis. These results suggest that the degree of clinical illness may be directly related to the cytotoxic effects of the virus and to the transmissibility of the disease.
  • Article
    Full-text available
    The effect of relative humidity (RH) on the airborne stability of two small bacterial viruses, S-13 and MS-2, was studied. Poorest recovery of S-13 was obtained at 50% RH. Humidification prior to aerosol sampling significantly increased the recovery of S-13 at RH deleterious to the airborne virus. A commercial preparation of MS-2 suspended in a buffered saline solution showed a rapid loss of viability at RH above 30%, whereas a laboratory preparation containing 1.3% tryptone showed high recoveries at all RH studied. Dilution of the commercial MS-2 into tryptone broth conferred stability on the airborne virus. Humidification prior to sampling significantly reduced the viable recovery from aerosols of commercial MS-2, whereas the laboratory preparation was unaffected.
  • Article
    A study was conducted at a secondary lead smelter to evaluate the workplace performance of the 3M W-344 and Racal AH3 powered air-purifying respirators equipped with helmets and high efficiency filters. The research protocol developed for the study has been described in a companion paper. The results of the study indicate that the mean lead concentrations, measured inside the facepiece of both PAPRs, were significantly less than the OSHA lead exposure limit of 50 micrograms/m3. The means of the workplace protection factor measurements on both PAPRs were significantly less than the PAPR selection guide protection factor classification of 1000. Correlation analysis of preshift quantitative fit factors and corresponding workplace protection factors indicated no linear association between these two measures of performance. This finding suggests that for PAPRs equipped with helmets and high efficiency filters quantitative fit factors as presently determined are not indicative of the workplace protection which the respirators provide. Since the PAPR protection factor classification of 1000 was originally based on quantitative fit factors, the lack of a demonstrated association between quantitative fit factors and workplace protection as found in this study may explain why their performance was significantly less than expected.
  • Article
    The bacterial and viral filtration performance of 12 breathing system filters was determined using test methods specified in the draft European standard for breathing system filters, BS EN 13328-1. All the filters were of two types, either pleated hydrophobic or electrostatic, and these two types differed in their filtration performance. The filtration performance is expressed in terms of the microbial penetration value, defined as the number of microbes passing through the filter per 10 million microbes in the challenge. The geometric mean (95% confidence limits) microbial penetration value was 1.0 (0.5, 3.5) and 2390 (617, 10 000) for the pleated hydrophobic and electrostatic filters, respectively, for the bacterial challenge, and 87 (48, 212) and 32 600 (10 900, 84 900), respectively, for the viral challenge. In general, there was little change in the microbial penetration values following 24 h simulated use. It is concluded that results from the tests specified in the draft standard will allow comparisons to be made between different manufacturers' products enabling an informed choice to be made.
  • Article
    Full-text available
    To measure the concentration of microbial aerosols in general dental practices and to use this information to carry out quantitative microbiological risk assessments. Microbial air sampling was carried out continuously during 12 treatment sessions in 6 general dental practices in the South West of England. The microbial aerosol concentration in treatment rooms was generally less than 10(3) colony forming units per cubic metre of air (cfu x m(-3)). However, in 6 out of the 12 visits, at least one peak concentration with much higher numbers of bacteria was detected. The peak concentrations were associated with increased recoveries of presumptive oral streptococci suggesting these aerosols originated from the mouths of patients. These aerosol peaks dissipated within 30 minutes and no dissemination into waiting areas was detected. The peak concentrations were associated with mechanical scaling procedures (47% of procedures giving rise to a peak) and to a lesser extent by cavity preparation (11%). No aerosolised blood was detected. The data have been used to generate a framework for quantifying risk of exposure of staff to aerosolised microbial pathogens in general dental practice. For example, dentists and their assistants may have a slightly higher risk of exposure to Mycobacterium tuberculosis than the general public. The use of face seal masks that have been shown to protect against aerosolised micro-organisms may reduce this exposure.