Influenza- Evaluating the Protection of Surgical Masks
Health and Safety Executive
The UK is preparing for a potential pandemic of influenza. The
main route of transmission of influenza virus is believed to be via
direct contact with large droplets from the nose and throat of an
infected person generated during coughing and sneezing. The
relative importance of small infectious droplets that are breathed
in (respiratory aerosols) to influenza transmission is considered
to be minor, but it cannot be ruled out. The current UK Pandemic
Influenza Infection Control Guidance recommends that procedures
likely to generate aerosols should be minimised or, where
unavoidable, health care workers should wear appropriate
respiratory protection. Health care workers who are in close
contact with patients should wear surgical masks to reduce exposure
to large droplets.
The use of surgical masks by health care workers is standard
practice to limit the spread of disease during outbreaks of
seasonal influenza. However, surgical masks are intended to protect
the patient from the wearer. In recent years, surgical masks have
been advocated for use as a protective barrier to protect the
wearer, but they are not intended to provide protection against
infectious aerosols. Work undertaken by HSL aimed to evaluate the
relative levels of protection provided by both surgical masks and
respirators against aerosols.
What We Did
This study focussed on the
effectiveness of surgical masks against a range of airborne
particles. We used separate tests to measure the reduction in
levels of inert particles and live aerosolised influenza virus
mitigated by surgical masks and properly fitted respirators.
- Live viruses could be detected in the air behind all surgical
- Surgical masks on average provide around a 6-fold reduction in
exposure to live aerosolised virus.
- The level of protection provided varied depending on the design
and construction of the mask and many of the surgical masks on the
NHS logistics list that we tested offered considerably less
protection than this.
- By contrast, properly fitted respirators could provide at least
a 100-fold reduction.
This work will assist those responsible for undertaking national
risk assessments for pandemic influenza outbreaks to better and
more cost effectively equip and protect front-line medical staff
when dealing with such an outbreak.
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