Legionnaires' Disease
Lewis Conquer Consultancy Services Limited are no longer
involved in Plant Hygiene Surveys for Legionella.
This page has been maintained in order to provide background information.
Legionnaires disease- causes and
epidemiology
Legal requirements in the UK for
controlling Legionnaires' disease
Health Effects
The term "Legionnaires' disease" was
coined in 1976 after a dramatic outbreak of serious respiratory disease at a
convention of the American Legion led to the discovery of a new disease entity
and, eventually, to the identification of the responsible bacteria,
Legionella pneumophila.
L. pneumophila, one of more than twenty currently
recognised species of the genus Legionella, is the species most commonly
implicated in cases reported both in Australia and overseas. Illnesses caused by
any species of Legionella are called Legionellosis. "Legionnaires' disease" is
the term used for the disease caused by L. pneumophila.
However, "Legionnaires' disease" has become the familiar term used to refer to
any severe form of pneumonia which is caused by a species of Legionella.
This form of pneumonia may be accompanied by involvement
of other organs such as the brain, causing confusion; the bowel, causing
diarrhoea; and the kidneys, causing kidney failure. Symptoms include rapid onset
of high fever, non-productive cough, chills, headache and general 'aches and
pains'. Positive identification can be achieved by isolating and identifying the
L. pneumophila from the patient's respiratory secretions or blood. The
incubation period, that is the time between infection and signs and symptoms
appearing, is usually 2-10 days. Less than 5 per cent of the exposed persons are
likely to become ill, but up to 30 per cent of these may die.
Pontiac fever, also caused by a species
of Legionella, is an influenza-like illness with symptoms including fever,
chills and headache. The incubation period ranges from 4 hours to 3 days. Up to
95 per cent of the exposed persons become ill. Pneumonia does not occur and full
recovery can be expected.
Many infections by L. pneumophila do not result in
recognisable signs and symptoms. Antibodies have been found in up to 25% of
adults tested. This suggests that up to I in 4 adults have been infected at some
time in their life but have not necessarily developed any symptoms.
Humidifier fever is not caused by Legionella, yet
it is often considered, incorrectly, as a form of Legionnaires' disease. This
influenza-like fever may result from the inhalation of micro-organisms that
cause allergic reactions. The potential source is often the humidifier of an air
conditioning system. Humidifier fever belongs to a group of illnesses known
collectively as hypersensitivity pneumonitis. Sensitisation to these microbial
contaminants occurs after a period of repeated daily exposures and the period
may vary from 1 month to a year or more.
It should be noted that the presence of fungi, algae,
protozoa and other bacteria in air-handling and water systems may contribute to
the:
- multiplication of the Legionella bacteria;
- emergence of diseases in addition to those associated
with the Legionella bacteria.
Sources of Infection
Legionella bacteria are widely distributed natural
inhabitants of waters. They have been found in lakes, rivers, creeks and other
bodies of water ranging in temperature up to 60 degrees C. However, significant
multiplication of these bacteria is generally restricted to temperatures of 20
degrees C to 45 degrees C and particularly to the range 35 degrees C to 43
degrees C. Systems with waters of this temperature range facilitate
proliferation.
The growth of L. pneumophila is promoted by the
presence of other micro organisms. Certain single-cell organisms are able to
amplify these bacteria in cooling towers as well as to protect them from adverse
conditions, including the biocidal action of water treatment chemicals. Other
bacteria and algae can provide nutrients for L. pneumophila. Sediments
can stimulate the growth of the environmental micro flora which, in turn,
stimulate the growth of L. pneumophila.
Investigations of the relationship between the chemical
environment in plumbing systems and growth of L. pneumophila.
has shown that low concentrations of certain metals such as iron, zinc and
potassium enhance proliferation of the species. Hence, the metal components and
corrosion products of plumbing systems (e.g. galvanised iron) may play a role in
promoting growth of these bacteria. The constituents of certain types of rubbers
used in rubber fittings in the system can also support the multiplication of
L. pneumophila.
The proliferation of L. pneumophila. occurs mainly
in water systems as a result of the inter-relationships between temperature,
environmental micro flora and sediments and the chemical composition of waters
in man-made systems.
In general, the sources of Legionella implicated in
outbreaks of Legionnaires' disease have been traced to large air conditioning
plants or to hot water distribution systems which have been incorrectly
commissioned or have been poorly maintained. The release of aerosols from water
distribution systems may occur from shower heads or from water splashing in hand
basins or baths. Standby installations would also be sources of infection if
they are used infrequently and not included in the general maintenance routine.
Other less common sources of infection that have been recorded include spa
pools, the coolant in industrial milling machines, high pressure cooling and
cleansing processes and humidification devices.
Potential sources of infection could include domestic air
conditioners, artesian bores, decorative fountains, fixed garden sprinklers, car
washes, and above ground storage tanks, which feed aerosol generating equipment,
although there have been no recorded cases from these sources.
Outbreaks of Legionnaires' disease are sporadic and the
source of the organisms is often very difficult to determine.
Mode of Transmission
The means by which these Legionella bacteria can infect
humans involves the formation of aerosol, the air transport of the aerosol into
the breathing zone of persons and the deposition of the aerosol in the lung.
Controlling the build up of
Legionella spp.
In the UK owners or occupiers of sites using equipment
that falls within the scope of the Notification of Cooling Towers and
Evaporative Condensers Regulations 1992 must inform the local authority
about the use of the plant.
Guidance and advice can be found in two HSE documents:
- HS(G) 70 The control of Legionellosis
including Legionnaires' Disease
- Approved code of Practice L8 The prevention
or control of Legionellosis (Including Legionnaires' Disease)
The second publication places responsibility on employers
to ensure the following:
- identify and assess the sources of risk
- prepare a scheme to prevent or control the risk
- implement and manage precautions
- keep records of the precautions implemented
Assessments should be reviewed if there is reason to
suspect that the original findings may no longer be valid e.g.:
- if there is a change to plant or water systems, or to
their use
- there are changes to the use of buildings in which
equipment is housed
- where new information concerning the risks or control
measures becomes available
- where the results of checks or tests show that
control measures are not effective
Exposure to harmful organisms, including Legionella, is
covered in the UK by the Control of Substances Hazardous to Health 1994
(COSHH), in the same way as these regulations cover the exposure to chemicals,
COSHH imposes the duty on an employer to ensure that employees are not exposed
to harmful substances, or where this is not practicable the exposure is
adequately controlled.
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