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Legionella : Legionnaires Disease A Risk Management Approach
6 May 2005 :: 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, and given the opportunity it can infest
and breed in your water systems, including cooling towers, air conditioners,
humidifiers, hot water systems and the like.
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
Solutions
Further Information
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