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

  • ... The filtration efficiency on various types of cloth masks has been tested using different size particles with ranges varying from 39% to 65% under laboratory conditions 40 and 48% to 83% using different household materials 41 . A recent study 42 aimed to evaluate the effectiveness of two-layered cotton masks compared to three-layered polypropylene surgical masks in filtering SARS-CoV-2 and found that both were ineffective in filtering the virus during coughs. ...
  • ... The open markets and public transport system should be regulated to avoid congestion. Till date, the effectiveness of face masks against the virus has not been examined; however, limited evidence from studies of other respiratory infections, such as influenza, shows that homemade masks confer to some degree of efficacy [49,50]. However, a preliminary study shows that SARS-CoV-2 transmission by infected persons is not prevented by wearing surgical and cotton masks [51]. ...
    Preprint
    The first coronavirus disease 2019 (COVID-19) case in Sub-Saharan Africa was reported in Nigeria on 27th February 2020, and within weeks the disease spread to all African countries, except Lesotho as of 1st May 2020. In this review, we have evaluated the public health measures initiated in sub-Saharan African countries to mitigate the spread of COVID-19, highlighted the impediments to these measures, and provided recommendations. We reviewed the strategies initiated in Nigeria, South Africa, Rwanda, and Burundi. It was found that the governments of these countries initiated several measures, including hand and respiratory hygiene, maintaing a distance from other people, quarantining travellers, and isolating symptomatic cases. Moreover, the lockdown was instituted to further reduce the spread of COVID-19 in Nigeria, South Africa, and Rwanda, while in Burundi there was no lockdown. However, the fragile medical infrastructure, poor living conditions, lack of social welfare system, draconian lockdown implementation strategies, and inconsistent information from authorities have impeded the success. The lockdown and social distancing measures have not reduced the rate of infection in these countries , and the implementation of the measures was sporadic and not backed up with increased capacities of diagnostic tests. It is strongly recommended that sub-Saharan African countries increase testing and follow scientific evidence in cautiously easing the lockdown, and develop postpandemic plans to revitalize the medical and socioeconomic infrastructure. In conclusion, the governments of these countries should look inward for solutions to their problems and avoid implementing western anti-COVID-19 policies without consideration of the peculiarities in African societies. ARTICLE HISTORY
  • ... The open markets and public transport system should be regulated to avoid congestion. Till date, the effectiveness of face masks against the virus has not been examined; however, limited evidence from studies of other respiratory infections, such as influenza, shows that homemade masks confer to some degree of efficacy [49,50]. However, a preliminary study shows that SARS-CoV-2 transmission by infected persons is not prevented by wearing surgical and cotton masks [51]. ...
  • ... We simplify the action space of the players as we did in the Bayesian game: in and out is merged into use, with efficiency parameters a and b. We set b = 2 3 , as surgical masks on the infectious person reduce cold & flu viruses in aerosols by 70% according to [12], while a home-made mask achieves 2/3 of this efficiency [4]. Parameter a is much harder to measure. ...
    Preprint
    Pandemic response is a complex affair. Most governments employ a set of quasi-standard measures to fight COVID-19 including wearing masks, social distancing, virus testing and contact tracing. We argue that some non-trivial factors behind the varying effectiveness of these measures are selfish decision-making and the differing national implementations of the response mechanism. In this paper, through simple games, we show the effect of individual incentives on the decisions made with respect to wearing masks and social distancing, and how these may result in a sub-optimal outcome. We also demonstrate the responsibility of national authorities in designing these games properly regarding the chosen policies and their influence on the preferred outcome. We promote a mechanism design approach: it is in the best interest of every government to carefully balance social good and response costs when implementing their respective pandemic response mechanism.
  • ... A. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? [18] 1) Authors: Anna Davies, Katy-Anne Thompson, Karthika Giri, George Kafatos, Jimmy Walker, and Allan Bennett, 2013 ...
    Preprint
    It is highly likely that the wearing of face masks reduces the rate of respiratory infections (e.g. SARS-CoV-2), to protect both the user and those around them. This paper sets out to review the areas that effect the efficacy of masks, the materials, design, hygiene and fit testing, in order to make recommendations as to how to make mask from resources found in most homes for when commercial models are unavailable. This paper finds that a mask constructed with a filter made from high thread count cotton is likely to provide a reasonable level of protection (~70% filtration) and that if a layers of other materials such as chiffon or silk is added the filtration may be much higher (~90%). There is also some promise in less available materials such as vacuum cleaner bags and air conditioner filters. Examples of fabric and rigid designs are reviewed but most are limited by the fit to the users which is hard to determine in a home setting. It would be extremely helpful if a method was devised for people to test or be tested for the fit of home made masks. In the mean time careful thought should be given to whether the user judges a good fit. Users should also be careful to practice other means of hygiene and distancing.
  • ... A confecção de máscaras caseiras também pode se dar pela reutilização de materiais do domicílio. Esta é a sequência para a escolha do tecido ideal em ordem crescente de filtragem de partículas virais, ou seja, da menos eficaz para a mais eficaz (Davies, Thompson, Kafatos, Walker & Bennett, 2013, Ministério da Saúde, 2020a: ...
    Book
    Full-text available
    Analisa as evidências existentes sobre o uso de máscaras caseiras, apresentar diferentes técnicas de confecção, modo de uso e desinfecção, a fim de educar a população em geral sobre as formas de minimizar o contágio pelo SARS-CoV-2 em situação de escassez de máscaras cirúrgicas e máscaras com filtros respiradores.
  • ... 26 Interestingly, the efficacy of home-made cotton masks was studied before by researchers who concluded that it could be used as a last resort to stop droplet transmission from infected persons with pandemic influenza when commercial masks could not be procured. 27 In stark contrast is the following statement from the WHO's interim guidance document explaining its stance on the type of mask: "The use of masks made of other materials (e.g., cotton fabric), also known as nonmedical masks, in the community setting has not been well evaluated. There is no current evidence to make a recommendation for or against their use in this setting". ...
  • ... The mask materials we used in this study were similar to a previous study in which the researchers evaluated the capacity of homemade masks to block bacterial and viral aerosols by using a fit test machine. Their results showed that 100% cotton from T-shirts was the best choice for homemade masks although its efficiency in blocking transmission was 3 times lower than that of surgical masks (9). A recent study also checked the filtration efficiency of common fabrics at two different airflows: ~35 L/min and ~90 L/min. ...
    Article
    Background: Sneezes produce many pathogen-containing micro-droplets with high velocities of 4.5-50.0 m/s. Face masks are believed to protect people from infection by blocking those droplets. However, current filtration efficiency tests can't evaluate masks under sneeze-like pressure. The goal of this study was to establish a method to evaluate the filtration efficiency of mask materials under extreme conditions. Materials and methods: Efficiency of surgical masks, gauze masks, gauze, cotton, silk, linen and tissue paper on blocking micro-droplet sized starch particles (average 8.2 μm) and latex microspheres (0.75 μm) with a velocity of 44.4 m/s created by centrifugation was qualitatively analyzed by using imaging-based analysis. Results: The 4 layers of silk could block 93.8% of microspheres and 88.9% of starch particles, followed by the gauze mask (78.5% of microspheres and 90.4% of starch particles) and the 2 layers of cotton (74.6% of microspheres and 87.5-89.0% of particles). Other materials also blocked 53.2-66.5% of microspheres and 76.4%-87.9% of particles except the 8 layers of gauze which only blocked 36.7% of particles. The filtration efficiency was improved by the increased layers of materials. Conclusion: Centrifugation-based filtration efficiency test not only compensates shortcomings of current tests for masks, but also offers a simple way to explore new mask materials during pandemics. Common mask materials can potentially provide protection against respiratory droplet transmission.
  • ... In past, different materials as the component of face mask have been explored w.r.t. their performance [28][29][30][31][32][33] . New designs need testing in a set-up which either is accessible at ease or can be made in a laboratory or industrial setting. ...
    Preprint
    Full-text available
    Recent crisis in the form of COVID-19 has rendered wearing a face mask mandatory for patients, health care workers and even members of public worldwide. This has caused a sudden shift of focus on availability, effectiveness, re-use and development of face masks. It is imperative that commercialization of face masks is subjected to certification, following standard procedures, from authorized agencies. However, at times, there is a need to conduct a quick investigation on their performance, specially, when new materials are being used for making the masks. In the current pandemic situation, the shortage of masks has also led to a rethinking on strategies of reuse of masks after due sterilization. For such situations, a quick laboratory methodology to test/determine the effectiveness of face mask respirators has been developed. The testing parameters include the particle capture efficiency of the mask material, pressure drop and the fit factor. Two different, simple, make-shift set-ups have been adopted for the present context. The first is used to measure the intrinsic particle capture efficiency and pressure drop of the filter material and the second is employed as a ‘full mask sampler’ to assess the leakages through seams and joints. For particle filtration efficiency, measurements in optical particle diameter range (0.3-20 µm) are most important as they cover the most penetrating particle size (MPPS) range; nevertheless, we also measured aerosol number concentration in sub-micrometer and ultrafine size ranges. Experiments conducted with atomized NaCl test aerosols, using these setups on three types of face masks viz. commercial N-95, surgical mask and cloth mask have been used for the validation and interpretation of results. This paper hopes to provide a crucial laboratory link between the face mask developers and the final certification agencies in the times of urgency.
  • 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.