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Legionella : Legionnaires Disease A Risk Management Approach
John Herbert | Director
Your building systems can harbour a particularly dangerous,
potentially fatal bacteria named Legionella Pneumophila,
more commonly known as Legionella.
Legionella is an aqueous organism, it lives in the nature,
given the opportunity it can infest and breed in your water
systems, including cooling towers, air conditioners, humidifiers, hot
water systems and other water systems.
Given the right environmental conditions Legionella will rapidly
multiply and reach a point where it could infect you, your staff or the
general public.
Legionella Control and Risk Management is a methodology to assess your potential risk.
What is Legionnaires' disease?
How do you get Legionnaires' disease?
Where do the Legionella bacteria come from?
How do Legionella outbreaks occur?
Background
Legionnaires' Disease (退
伍軍人病) is a form of pneumonia that may have serious
consequences for some people, especially people in the older age groups
and those otherwise susceptible to disease.
Legionellosis is a term used to describe any illness caused
by the Legionella bacterium.
The bacterium responsible for legionnaires
disease was initially
identified in 1977, by the CDC in Atlanta, following a large outbreak
at a Bellevue Stanford hotel, Philadelphia, USA in July 1976.
The disease was named from the group of people
primarily affected in
this outbreak. They were retired American service personnel who were
attending a legion convention at the stricken hotel.
Since this first outbreak, sporadic cases and
major outbreaks have been
regularly reported across the globe, many of them linked to hotels,
healthcare, and holiday accommodation.
What is Legionnaires' disease?
Legionnaires disease is a severe form of pneumonia. The disease has no
particular clinical features
that clearly distinguishes it from other types of pneumonia, therefore
only
laboratory tests can confirm the diagnosis.
It normally takes between 2-10 days to develop
symptoms (typically five
to six days but very rarely some cases may take two to three weeks to
develop symptoms).
Patients usually start with a dry cough, fever, headache
and sometimes diarrhoea and then pneumonia. The literature states that
people over the age of 50 are more at risk than younger people and
males more than females. Although discovered nearly thirty years old,
little is known, and the indications are that the age pre-disposition
is not an important factor as once thought, even Neonates have
contracted Legionnaires disease.
Effective antibiotic treatment is available if the diagnosis is made
early in the illness. Death occurs in about 5-15% of people who get the
disease, depending on their age and individual health status. Smokers
are more at risk than non-smokers. If patients in hospitals contracted
Legionnaires disease the mortality risk increases up to 40%.
How do you get Legionnaires' disease?
People are infected when they breathe air that contains tiny
droplets of water, known as aerosols, inside of which are the
Legionella bacteria.
If the bacteria is inhaled deep into the lungs infection could follow.
Legionnaires disease cannot be caught from water you drink that enters
your stomach in the normal way – the bacterium has to get into
the lungs through breathing it in.
Spread from person to person has not been documented.
The infectious dose is not known, although outbreaks traced
back to a source many kilometres away indicate that the infectious dose
maybe only be one bacteria.
Where do the Legionella bacteria come from?
Legionella is common, found naturally in
environmental water sources
such as rivers, groundwater, lakes and reservoirs, usually in low
numbers.
When the bacteria enter domestic water systems used in our
buildings, they sometimes cause a risk to humans if people get exposed
to them through air conditioning or air cooling systems, or through
contaminated water systems used for baths or showers, etc.
How do outbreaks occur?
Experience indicates that outbreaks are associated with
cooling towers, or domestic water distribution systems.
If the bacteria is in the water in quantities that can
cause infection, someone taking a shower would inhale the bacteria
trapped inside the tiny aerosols that are created when the shower water
hits the hard surfaces of the shower unit or bath. They may also be
affected by other water systems that cause aerosols, for example
whirlpool spas and fountains.
In contrast, large explosive outbreaks in the community are
mostly associated with cooling towers. Cooling towers are devices used
to cool buildings.
They are also called “wet air conditioning
systems” because the process of cooling air involves
extensive contact between water and air, thereby creating aerosols.
When the Legionella bacteria are present in
these systems they can
cause legionnaires’ disease. Air conditioning units that use
water to cool the air can also pose a risk.
However, many air conditioning systems are
“dry” and these pose no risk for
legionnaires’ disease.
When an outbreak of legionnaires disease occurs, the source
may be found through two types of investigation.
One collects information on the activities and
whereabouts of the
patients with legionnaires' disease to look for links between cases
such as staying at or visiting the same places before they became ill.
The other involves looking for the Legionella bacteria in
the suspected water sources and in clinical specimens from the
patients. If the bacteria are found in both, specialised laboratory
methods are used to see if they are of the same type.
Sources of Legionella Infection
The media tends to only report the explosive Legionella outbreaks which tends to be misleading when you consider the range of equipment and devices that have been associated Legionella infection.
Here is a table complied by Director John Herbert, citing devices and equipment, with references, that have caused Legionella Infection Legionnaires Disease (3 pages PDF format).
Video
Click on this link to learn more about how Legionella causes infection and once inside the lung how Legionella grows: Legionella infection and multiplication video
Prevention Solutions
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Further Information
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