ArticlePDF Available

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

Authors:

Abstract and Figures

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).
Content may be subject to copyright.
DisasterMedicineandPublicHealthPreparedness
http://journals.cambridge.org/DMP
AdditionalservicesforDisasterMedicineandPublicHealthPreparedness:
Emailalerts:Clickhere
Subscriptions:Clickhere
Commercialreprints:Clickhere
Termsofuse:Clickhere
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
DisasterMedicineandPublicHealthPreparedness/FirstViewArticle/July2013,pp16
DOI:10.1017/dmp.2013.43,Publishedonline:22May2013
Linktothisarticle:http://journals.cambridge.org/abstract_S1935789313000438
Howtocitethisarticle:
AnnaDavies,KatyAnneThompson,KarthikaGiri,GeorgeKafatos,JimmyWalkerandAllanBennettTestingtheEfficacy
ofHomemadeMasks:WouldTheyProtectinanInfluenzaPandemic?.DisasterMedicineandPublicHealth
Preparedness,AvailableonCJO2013doi:10.1017/dmp.2013.43
RequestPermissions:Clickhere
Downloadedfromhttp://journals.cambridge.org/DMP,IPaddress:80.5.24.130on25Jul2013
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).
REFERENCES
1. MacIntyre CR, Cauchemez S, Dwyer DE, et al. Face mask use and
control of respiratory virus transmission in households. Emerg Infect Dis.
2009;15:233-241.
2. Wilkes A, Benbough J, Speight S, Harmer M. The bacterial and
viral filtration performance of breathing system filters. Anaesthesia.
2000;55:458-465.
3. Cox C. The Aerobiological Pathway of Microorganisms. Chichester, UK:
John Wiley & Sons; 1987.
4. Sharp RJ, Scawen MD, Atkinson A. Fermentation and downstream
processing of Bacillus. In: Harwood CR, ed. Bacillus. New York, NY:
Plenum Publishing Corporation; 1989.
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness 5
5. Dubovi EJ, Akers TA. Airborne stability of tailless bacterial viruses S-13
and MS-2. Appl Microbiol. 1970;19:624-628.
6. Stanley WM. The size of influenza virus. J Exp Med. 1944;79:267-283.
7. Myers WR, Peach III MJ, Cutright K, Iskander W. Workplace protection
factor measurements on powered air-purifying respirators at a secondary lead
smelter: results and discussion. Am Industrial Hygiene Assoc J. 1984;45:681-688.
8. Andersen AA. New sampler for the collection, sizing and enumeration of
viable airborne particles. J Bacteriol. 1958;76:471-484.
9. Bourdillon RB, Lidwell CM, Thomas JC. A slit sampler for collecting
and counting airborne bacteria,. J Hygiene. 1941;14:197-224.
10. Lavoie J, Cloutier Y, Lara J, Marchand G. Guide on Respiratory Protection
Against Bioaerosols–Recommendations on Its Selection and Use. Quebec,
Canada: IRSST; 2007.
11. van der Sande M, Teunis P, Sabel R. Professional and home-made
face masks reduce exposure to respiratory infections among the general
population. PLoS ONE. 2008;3:e2618.
12. Wilkes AR, Benbough JE, Speight SE, Harmer M. The bacterial
and viral filtration performance of breathing system filters. Anaesthesia.
2000;55:458-465.
13. Bennett AM, Fulford MR, Walker JT, et al. Microbial aerosols in general
dental practice. Br Dent J. 2000;189:664-667.
14. Hall CB, Douglas RG Jr, Geiman JM, Meagher MP. Viral shedding
patterns of children with influenza B infection. J Infect Dis. 1979;140:
610-613.
15. Clayton MP, Bancroft B, Rajan B. A review of assigned protection
factors of various types and classes of respiratory protective equipment
with reference to their measured breathing resistances. Ann Occup Hyg.
2002;46:537-547.
16. Syed Q, Sopwith W, Regan M, Bellis MA. Behind the mask:
journey through an epidemic: some observations of contrasting public
health responses to SARS. J Epidemiol Community Health. 2003;57:
855-856.
Are Homemade Masks Effective?
Disaster Medicine and Public Health Preparedness6
... However, the ability of masks both to protect others from transmission from the wearer and to protect the wearer from transmission from others depends on several variables, including the material used, the construction (e.g. layers of material), and the quality of fit 43,45,46 . Therefore, we consider scenarios where there is low, medium, and high protection of others from the wearer ( ...
... Since masks reduce transmission for all infections, irrespective of symptoms, masks work synergistically with household quarantine. While we consider scenarios where masks block <20% of transmission, we note that this is a worst case scenario; experimental work suggests that our mid-to high-quality mask scenarios (blocking 50-80% of transmission) are more likely 45,46 . Observational 53,54 and other modelling 44 studies provide further evidence for the effectiveness of masks in blocking transmission. ...
Preprint
Full-text available
Background Non-pharmaceutical interventions (NPIs) used to limit SARS-CoV-2 transmission vary in their feasibility, appropriateness and effectiveness in different contexts. In Bangladesh a national lockdown implemented after the first detected case in early March 2020 rapidly exacerbated poverty and was considered untenable long-term, whilst surging cases in 2021 warrant renewed NPIs. We examine potential outcomes and costs of NPIs considered appropriate and feasible to deploy in Dhaka over the course of the pandemic including challenges of compliance and scale up. Methods We developed an SEIR model for application to Dhaka District, parameterised from literature values and calibrated to death data from Bangladesh. We discussed scenarios and parameterizations with policymakers using an interactive app, to guide modelling of lockdown and post-lockdown measures considered feasible to deliver; symptoms-based household quarantining and compulsory mask-wearing. We examined how testing capacity affects case detection and compared deaths, hospitalisations relative to capacity, working days lost from illness and NPI compliance, and cost-effectiveness. Results Lockdowns alone were predicted to delay the first epidemic peak but were unable to prevent overwhelming of the health service and were extremely costly. Predicted impacts of post-lockdown interventions depended on their reach within communities and levels of compliance: symptoms-based household quarantining alone was unable to prevent hospitalisations exceeding capacity whilst mask-wearing could prevent overwhelming health services and be cost-effective given masks of high filtration efficiency. The modelled combination of these measures was most effective at preventing excess hospitalizations for both medium and high filtration efficiency masks. Even at maximum testing capacity, confirmed cases far underestimate total cases, with saturation limiting reliability for assessing trends. Recalibration to surging cases in 2021 suggests limited immunity from previous infections and the need to re-sensitize communities to increase mask wearing. Conclusions Masks and symptoms-based household quarantining act synergistically to prevent transmission, and are cost-effective in mitigating impacts. Our interactive app was valuable in supporting decision-making in Bangladesh, where mask-wearing was mandated early, and community teams have been deployed to support household quarantining across Dhaka. This combination of measures likely contributed to averting the worst impacts of a public health disaster as predicted under an unmitigated epidemic, but delivering an effective response at scale has been challenging. Moreover, lack of protection to the B.1.351 variant means messaging to improve mask-wearing is urgently needed in response to surging cases.
... Several studies have measured FE, breathing resistance, Quality Factor (QF) for a variety of masks (Konda et al. 2020;MacIntyre et al. 2015;Sande et al. 2008;Rengasamy et al. 2010;Zangmeister et al. 2020;Davies et al. 2013). These studies do not cover the almost unlimited available design possibilities. ...
... According to Figure 4, nonwoven fabrics were the ones that presented the best performance in filtration among the nonprofessional masks following (Kutter et al., 2018;Davies et al., 2013). The microstructure of nonwoven fabrics and their layers and fibers cannot be adequately distinguished by digital optical microscopy; thus, scanning electron microscopy is required to characterize this fabric type. ...
Article
Full-text available
The use of face masks is mandatory in public places in many countries to slow the spread of the COVID-19 pandemic. In developing countries, homemade masks with varying techniques and fabrics are used on the streets. On these fabric masks, the protection against SARS-CoV-2 varies significantly. The most common mask types are N95, surgical masks, and homemade nonwoven and cotton masks. The performance of 227 different face masks used in Brazil was evaluated to quantify their breathability and filtration efficiency (FE) for airborne particles. FE values were measured using NaCl aerosol particles sized from 60 to 300 nm and at 300 nm, minimum efficiency. The differential pressure drop over the mask and the FEmin at 300 nm was used to calculate the mask Quality Factor (QF). The N95 masks showed the highest FE60-300, around 0.98, and a QF of 13.2 KPa⁻¹, and were considered the reference for evaluating homemade masks performance. Surgical masks have an FE60-300 of 0.89, with a good QF of 15.9 KPa⁻¹. Nonwoven masks showed an average FE60-300 of 0.78, with an excellent QF of 24.9 KPa⁻¹, and can be regarded as the best material for homemade masks. The most commonly used material for homemade masks, cotton fabrics, showed significant variability in FE60-300, ranging from a low 0.20 to 0.60, with a low QF of 1.4 KPa⁻¹. Masks always reduce droplets and aerosols emitted by COVID-19 symptomatic and asymptomatic persons, reducing SARS-CoV-2 contamination.
... 12 APRIL 2021 | Volume 2 | Issue 1 The efficacy of homemade cloth masks made from knitted cotton fabric, compared to surgical masks, was assessed to determine if they would be effective in an influenza epidemic (H1N1). The results of the study, which compared the bacterial filter efficiency (BFE) and pressure drop, are seen in Table 4. 13 The efficacy of homemade cloth masks made from knitted cotton fabric, compared to surgical masks, was assessed to determine if they would be effective in an influenza epidemic (H1N1). 13 The results of the study, which compared the bacterial filter efficiency (BFE) and pressure drop, are seen in Table 4. Bacterial agents were used as proxies for the H1N1 virus, and the data indicate that homemade masks made from knitted cotton fabric should not be used for the reduction of transmission from diseases which can be transmitted via mucosalivary secretions. ...
... The results of the study, which compared the bacterial filter efficiency (BFE) and pressure drop, are seen in Table 4. 13 The efficacy of homemade cloth masks made from knitted cotton fabric, compared to surgical masks, was assessed to determine if they would be effective in an influenza epidemic (H1N1). 13 The results of the study, which compared the bacterial filter efficiency (BFE) and pressure drop, are seen in Table 4. Bacterial agents were used as proxies for the H1N1 virus, and the data indicate that homemade masks made from knitted cotton fabric should not be used for the reduction of transmission from diseases which can be transmitted via mucosalivary secretions. Tables 2, 3, and 4 suggest the relative ineffectiveness of masks made from cloth fabrics without filters. ...
Article
The widespread respiratory transmission of the Covid-19 virus has taught us the importance of face masks to mitigate both the community spread of the virus and protection of wearers by face masks. As such, there could be an extremely adverse public health possibility where respiratory pathogenic agents could be spread as a means of bioterrorism. While eventually vaccines could mitigate wide spread infection, protective face masks are an important way to immediately prevent respiratory infections from various pathogenic agents. In view of the possibility of respiratory-based bioterrorism it is critical that the public might have to adopt universal usage of face masks. The CDC recommends that all families stockpile respiratory protection as part of their personal pandemic plan because face masks should be worn by all individuals during a pandemic especially one caused by bioterrorism.
... Several studies have been conducted to determine the efficacy of cloth masks in reducing the spread of respiratory infection in the community. The study conducted by Davies et al. (29) aimed to evaluate the capacity of homemade masks (made of several types of textile) as alternatives to surgical masks as a physical barrier against bacteria and viral aerosols. This study determined the filtration efficiency of various types of cloth, such as cotton T-shirt fabric, linen, silk, and scarfs in comparison with surgical masks against two types of organism, namely Bacillus atrophaeus (0.95-1.25 m in diameter) and bacteriophage MS2 (23 nm in diameter). ...
... These study results also showed that the use of home-made masks was better than not wearing any mask at all. (29) The study conducted by Jung et al. (30) aimed to evaluate the filtration capacity of various types of masks, using the protocols of the Korean Food and Drug Administration (KFDA) and the US National Institute for Occupational Safety and Health (NIOSH). Cloth masks made from cotton handkerchiefs consisting of minimally four layers, had a filtration efficiency of only 13%, whereas extremely porous textiles such as gauze, had a filtration efficiency of merely 3%, even though consisting of several layers. ...
Article
Full-text available
Since the outbreak in Wuhan City, China, in late December 2019, the Coronavirus Disease 2019 (COVID-19) has spread to nearly the whole world, so that it was declared a pandemic by the Word Health Organization. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative organism of COVID-19, is extremely infectious and can adhere to droplet nuclei of < 5 mm diameter and become airborne (aerosol). Since COVID-19 was declared a pandemic, there has been controversy on the use of cloth masks by the public, because of the still inconclusive evidence of the efficacy of cloth masks in protecting against COVID-19 transmission. Universal masking as a healthcare intervention in the community is currently made mandatory by local governments of most countries, since they follow the recent recommendation by the World Health Organization. The issuing of the WHO recommendation on the public use of masks was based on a study demonstrating that COVID-19 transmission does not occur only through droplets but also through aerosols. In addition, there was a study showing that COVID-19 transmission does not only occur from patients with clinical symptoms but also through asymptomatic and pre-symptomatic subjects, so that universal masking is of benefit in providing protection when used by healthy people and as source control to prevent cross-transmission to other people. This review article aims to discuss the mechanism of COVID-19 transmission, the evidence related to the efficacy of cloth masks, and the guidelines related to the selection and use of masks by the general population.
... The other cases are based on real-world indoor spaces or reasonable estimation. r E and r B are estimated mostly based on the typical values for all-age-group averages in Table SI (38,76), and use of additional virus-removing devices (e.g. HEPA filter) with λ cle = 3 h -1 . ...
Preprint
Full-text available
Some infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Although physical distancing effectively reduces short-range airborne transmission, many infections have occurred when sharing room air despite maintaining distancing. We propose two simple parameters as indicators of infection risk for this situation. They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and air cleaning rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend in relation to these parameters that is consistent with an airborne infection model, supporting the importance of airborne transmission for these outbreaks. The observed trends of outbreak size vs. risk parameters allow us to recommend values of the parameters to minimize COVID-19 indoor infection risk. All of the pre-pandemic spaces are in a regime where they are highly sensitive to mitigation efforts. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at much higher risk parameter values. Since both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include ventilation information, to allow expanding our knowledge of the circumstances conducive to airborne transmission of different diseases.
... [8,10] Studies using healthy human subjects have shown that cloth face masks partially block respiratory aerosols produced during coughing, breathing and talking. [11,12] Two studies of patients with respiratory infections found that medical face masks reduced the dispersion of potentially infectious aerosols. [13,14] Although face masks do not protect the wearer from airborne particles as effectively as a respiratory protective device such as a N95 filtering facepiece respirator, they do reduce the wearer's exposure to infectious droplets and aerosols. ...
Preprint
Full-text available
Face masks reduce the spread of infectious respiratory diseases such as COVID-19 by blocking aerosols produced during coughs and exhalations (“source control”). Masks also slow and deflect cough and exhalation airflows, which changes the dispersion of aerosols. Factors such as the directions in which people are facing (orientation) and separation distance also affect aerosol dispersion. However, it is not clear how masking, orientation, and distance interact. We placed a respiratory aerosol simulator (“source”) and a breathing simulator (“recipient”) in a 3 m x 3 m chamber and measured aerosol concentrations for different combinations of masking, orientation, and separation distance. When the simulators were front-to-front during coughing, masks reduced the 15-minute mean aerosol concentration at the recipient by 92% at 0.9 and 1.8 m separation. When the simulators were side-by-side, masks reduced the concentration by 81% at 0.9 m and 78% at 1.8 m. During breathing, masks reduced the aerosol concentration by 66% when front-to-front and 76% when side-by-side at 0.9 m. Similar results were seen at 1.8 m. When the simulators were unmasked, changing the orientations from front-to-front to side-by-side reduced the cough aerosol concentration by 59% at 0.9 m and 60% at 1.8 m. When both simulators were masked, changing the orientations did not significantly change the concentration at either distance during coughing or breathing. Increasing the distance between the simulators from 0.9 m to 1.8 m during coughing reduced the aerosol concentration by 25% when no masks were worn but had little effect when both simulators were masked. During breathing, when neither simulator was masked, increasing the separation reduced the concentration by 13%, which approached significance, while the change was not significant when both source and recipient were masked. Our results show that universal masking reduces exposure to respiratory aerosol particles regardless of the orientation and separation distance between the source and recipient.
... Some papers are based on the classical efficiency measurement method (i.e. applied according to standards) in an attempt to estimate the effectiveness of these facemasks [10] [11] [12] [13]. They show that wearing a mask reduces the amount of aerosol generated downstream of the mask. ...
Article
Full-text available
The World Health Association and many governmental agencies recommend the wearing of facemasks by the general public to prevent the spread of COVID-19. It is believed that masks can significantly protect others and may offer some protection to the wearer. Although there are standards for FFRs, surgical masks, and recently for barrier face coverings, they all indicate the level of protection for the wearer. However, testing facial masks not at the point of inhalation, but at the source, the exhale, offers a new perspective on how to impede particle emissions. In this paper, the experimental results show that, although the barrier face covering is less effective than FFRs or surgical masks, it can reduce the concentration of aerosols downstream of the device. The results on barrier efficiency show a rapid decrease in effectiveness when the face covering is not sealed to the head. The barrier efficiency of two of the barrier face coverings tested is strongly dependent on leakage caused by the fit rather than the material. While some materials certainly are more effective than others in inhibiting particle penetration, an even more profound factor is the amount of leakage emitted from a mask. New approaches to fit and design in order to create a seal against leakage will become an important factor in combatting SARS-CoV-2.
... The different types of masks are shown in Table 2representingits characteristicsdefining the filtration range based on theparticle size, and on this ground, area of usageis specified, and further, the findingsareanalyzed. [71,72] Health care workers have been working day and night restlessly to serve humanity. The face masks worn by them as a piece of personal protective equipment for protection from infections can affect the efficacy of their work. ...
Article
Full-text available
Introduction The advent of COVID-19 has impinged millions of people. The increased concern of the virus spread in confined spaces due to meteorological factors has sequentially fostered the need to improve indoor air quality. Objective This paper aims to review control measures and preventive sustainable solutions for the future that can deliberately help in bringing down the impact of declined air quality and prevent future biological attacks from affecting the occupant’s health. Methodology Anontology chart is constructed based on the set objectives and review of all the possible measures to improve the indoor air quality taking into account the affecting parameters has been done. Observations An integrated approach considering non-pharmaceutical and engineering control measures together for a healthy indoor environment should be contemplated rather than discretizing the available solutions. Maintaining social distance by reducing occupant density and implementing a modified ventilation system with advance filters for decontamination of viral load can help in sustaining healthy indoor air quality. Conclusion The review paper in the main, provides a brief overview of all the improvement techniques bearing in mind thermal comfort and safety of occupants and looks for a common ground for all the technologies based on literature survey and offers recommendation for a sustainable future.
... While all masks are protective for Influenza, homemade masks produced from tea clothes provided two times less protection than surgical masks and 50 times less than FFP2 respirators [18]. Similarly, surgical masks presented better filtration efficiency and generally reduced the total amount of microorganisms expelled by coughing, compared to homemade masks of different materials [19]. For COVID-19, a surgical mask barrier significantly reduced transmission or produced fewer clinical manifestations in Golden Syrian Hamster [20]. ...
Article
Full-text available
Many governments have imposed the public use of face masks and they are now moving towards enforcing disposable masks to abate COVID-19 transmission. While disposable masks consistently provide higher protection, they also carry multiple environmental burdens, from greenhouse gases released during production to the landfilling and littering. Conversely, reusable masks’ protection can vary from >90% certified industrial masks, similar to disposable masks, to dubious homemade or artisanal masks. This work discusses the protection provided by different masks, their impact on the environment, and new proposals combining concerns about public health and sustainability.
Article
In response to personal protective equipment (PPE) shortages in the United States due to the Coronavirus Disease 2019, two models of N95 respirators were evaluated for reuse after gamma radiation sterilization. Gamma sterilization is attractive for PPE reuse because it can sterilize large quantities of material through hermetically sealed packaging, providing safety and logistic benefits. The Gamma Irradiation Facility at Sandia National Laboratories was used to irradiate N95 filtering facepiece respirators to a sterilization dose of 25 kGy(tissue). Aerosol particle filtration performance testing and electrostatic field measurements were used to determine the efficacy of the respirators after irradiation. Both respirator models exhibited statistically significant decreases in particle filtering efficiencies and electrostatic potential after irradiation. The largest decrease in capture efficiency was 40–50% and peaked near the 200 nm particle size. The key contribution of this effort is correlating the electrostatic potential change of individual filtration layer of the respirator with the decrease filtration efficiency after irradiation. This observation occurred in both variations of N95 respirator that we tested. Electrostatic potential measurement of the filtration layer is a key indicator for predicting filtration efficiency loss.
Article
Full-text available
Objective To measure the concentration of microbial aerosols in general dental practices and to use this information to carry out quantitative microbiological risk assessments.Methodology Microbial air sampling was carried out continuously during 12 treatment sessions in 6 general dental practices in the South West of England.Results The microbial aerosol concentration in treatment rooms was generally less than 103 colony forming units per cubic metre of air (cfu.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.Conclusions 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.
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
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.
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
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
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.