The use of masks for the general public :-
Studies
of influenza, influenza-like illness, and human corona viruses (not including
COVID-19) provide evidence that the use of a medical mask can prevent the
spread of infectious droplets from a symptomatic infected person (source
control) to someone else and potential contamination of the environment by these
droplets.
There
is limited evidence that wearing a medical mask by healthy individuals in
households, in particular those who share a house with a sick person, or among
attendees of mass gatherings may be beneficial as a measure preventing transmission.
A recent meta-analysis of these observational
studies, with the intrinsic biases of observational data, showed that either
disposable surgical masks or reusable 12–16-layer cotton masks were associated
with protection of healthy individuals within households and among contacts of
cases.
This could be considered to be
indirect evidence for the use of masks (medical or other) by healthy
individuals in the wider community; however, these studies suggest that such
individuals would need to be in close proximity to an infected person in a
household or at a mass gathering where physical distancing cannot be achieved,
to become infected with the virus. Results from cluster randomized controlled
trials on the use of masks among young adults living in university residences
in the United States of America indicate that face masks may reduce the rate of
influenza-like illness, but showed no impact on risk of laboratory-confirmed
influenza.
At
present, there is no direct evidence (from studies on COVID19 and in healthy
people in the community) on the effectiveness of universal masking of healthy
people in the community to prevent infection with respiratory viruses,
including COVID-19. WHO regularly monitors all emerging evidence about this
important topic and will provide updates as more information becomes available.
Types of mask to consider :-
(1) Medical
mask :
Medical
masks should be certified according to international or national standards to
ensure they offer predictable product performance when used by health workers,
according to the risk and type of procedure performed in a health care setting.
Designed
for single use, a medical mask’s initial filtration (at least 95% droplet
filtration), breathability and, if required, fluid resistance are attributed to
the type (e.g. spunbond or meltblown) and layers of manufactured non-woven
materials (e.g. polypropylene, polyethylene or cellulose).
Medical masks are rectangular in shape and
comprise three or four layers. Each layer consists of fine to very fine fibres.
These masks are tested for their ability to block droplets (3 micrometres in
size; EN 14683 and ASTM F2100 standards) and particles (0.1 micrometre in size;
ASTM F2100 standard only).
The
masks must block droplets and particles while at the same time they must also
be breathable by allowing air to pass. Medical masks are regulated medical
devices and categorized as PPE. The use of medical masks in the community may
divert this critical resource from the health workers and others who need them
the most. In settings where medical masks are in short supply, medical masks
should be reserved for health workers and at-risk individuals when indicated.
(2) Non-medical mask :-
Non-medical
(also referred to as “fabric” in this document) masks are made from a variety
of woven and non-woven fabrics, such as polypropylene. Non-medical masks may be
made of different combinations of fabrics, layering sequences and available in
diverse shapes. Few of these combinations have been systematically evaluated
and there is no single design, choice of material, layering or shape among the
nonmedical masks that are available.
The
unlimited combination of fabrics and materials results in variable filtration
and breathability. A non-medical mask is neither a medical device nor personal
protective equipment. However, a non-medical mask standard has been developed
by the French Standardization Association (AFNOR Group) to define minimum
performance in terms of filtration (minimum 70% solid particle filtration or
droplet filtration) and breathability (maximum pressure difference of 0.6
mbar/cm2 or maximum Advice on the use of masks in the context of COVID-19:
Interim guidance -9- inhalation resistance of 2.4 mbar and maximum exhalation
resistance of 3 mbar).
The
lower filtration and breathability standardized requirements, and overall
expected performance, indicate that the use of non-medical masks, made of woven
fabrics such as cloth, and/or non-woven fabrics, should only be considered for
source control (used by infected persons) in community settings and not for
prevention. They can be used ad-hoc for specific activities (e.g., while on
public transport when physical distancing cannot be maintained), and their use
should always be accompanied by frequent hand hygiene and physical distancing.
Decision
makers advising on type of non-medical mask should take into consideration the
following features of nonmedical masks: filtration efficiency (FE), or
filtration, breathability, number and combination of material used, shape,
coating and maintenance.
(a) Type of materials: filtration
efficiency (FE), breathability of single layers of materials, filter quality
factor The selection of material is an important first step as the filtration
(barrier) and breathability varies depending on the fabric. Filtration
efficiency is dependent on the tightness of the weave, fibre or thread
diameter, and, in the case of nonwoven materials, the manufacturing process
(spunbond, meltblown, electrostatic charging).
The
filtration of cloth fabrics and masks has been shown to vary between 0.7% and
60%.(73, 74) The higher the filtration efficiency the more of a barrier
provided by the fabric. Breathability is the ability to breathe through the
material of the mask. Breathability is the difference in pressure across the
mask and is reported in millibars (mbar) or Pascals (Pa) or, for an area of
mask, over a square centimeter (mbar/cm2 or Pa/cm2 ). Acceptable breathability
of a medical mask should be below 49 Pa/cm2 .
For
non-medical masks, an acceptable pressure difference, over the whole mask,
should be below 100 Pa.(73) Depending on fabric used, filtration efficiency and
breathability can complement or work against one another. Recent data indicate
that two non-woven spunbond layers, the same material used for the external
layers of disposable medical masks, offer adequate filtration and
breathability. Commercial cotton fabric masks are in general very breathable
but offer lower filtration.
The
filter quality factor known as “Q” is a commonly used filtration quality
factor; it is a function of filtration efficiency (filtration) and
breathability, with higher values indicating better overall efficiency.(76)
Table 3 shows FE, breathability and the filter quality factor, Q, of several
fabrics and non-medial masks.(73, 77) According to expert consensus three (3)
is the minimum Q factor recommended. This ranking serves as an initial guide
only
Disadvantages of the use of mask by healthy people :-
Potential harms/disadvantages
The likely disadvantages of the use of mask by healthy people in the general
public include:
Ø potential
increased risk of self-contamination due to the manipulation of a face mask and
subsequently touching eyes with contaminated hands.
Ø potential
self-contamination that can occur if nonmedical masks are not changed when wet
or soiled. This can create favourable conditions for microorganism to amplify.
Ø potential
headache and/or breathing difficulties, depending on type of mask used.
Ø potential
development of facial skin lesions, irritant dermatitis or worsening acne, when
used frequently for long hours.
Ø difficulty
with communicating clearly.
Ø potential
discomfort .
Ø a
false sense of security, leading to potentially lower adherence to other
critical preventive measures such as physical distancing and hand hygiene.
Ø poor
compliance with mask wearing, in particular by young children;
Ø waste
management issues; improper mask disposal leading to increased litter in public
places, risk of contamination to street cleaners and environment hazard;
Ø difficulty
communicating for deaf persons who rely on lip reading;
Ø disadvantages
for or difficulty wearing them, especially for children, developmentally
challenged persons, those with mental illness, elderly persons with cognitive
impairment, those with asthma or chronic respiratory or breathing problems,
those who have had facial trauma or recent oral maxillofacial surgery, and
those living in hot and humid environments.
(Source World Health
Organization)
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