Legionnaires' Disease
Cooling Towers
and Evaporative Condensers
What is Legionnaires' disease?
Legionnaires' disease is a type of pneumonia. It was named after
an outbreak of severe pneumonia that affected a meeting of the
American Legion in 1976. It is an uncommon but serious disease.
Legionnaires' disease occurs more frequently in men than women.
It usually affects middle-aged or elderly people, and it more
commonly affects smokers or people with other chest problems.
About half the cases of Legionnaires' disease are caught abroad
- useful advice on travel can be obtained from the European Working Group for Legionella
Infections. The other half are the result of infections
acquired in the UK.
How do people get it?
The agent that causes Legionnaires' disease is a bacterium
called Legionella pneumophilia. People catch Legionnaires' disease
by inhaling small droplets of water suspended in the air, which
contain the bacteria.
Certain conditions increase the risk from legionella:
- a suitable temperature for growth, 20 to 45oC;
- a source of nutrients for the organism, eg sludge, scale, rust,
algae, and other organic matter;and
- a way of creating and spreading breathable droplets, eg the
aerosol created by a cooling tower or spa pool.
However, remember that most people exposed to legionella
do not become ill, and Legionnaires' disease does
not spread from person to person.
What are the symptoms?
The symptoms of Legionnaires' disease are similar to those of
flu:
- high temperature, fever and chills;
- cough;
- muscle pains; and
- headache.
In a bad case there may also be pneumonia, and occasionally
diarrhoea and signs of mental confusion.
Where does it come from?
Legionella bacteria are widespread in nature, mainly living in
natural water systems, eg rivers and ponds. However, the conditions
are rarely right for people to catch the disease from these
sources.
Outbreaks of the illness occur from exposure to legionella
growing in purpose-built systems where the water is maintained at a
temperature high enough to encourage growth, eg cooling towers,
evaporative condensers, spa pools, and hot water systems used in
all sorts of premises (work and domestic).
Most community outbreaks in the UK have been linked to
installations such as cooling towers, which can spread droplets of
water over a wide area. These are found as part of air-conditioning
and industrial cooling systems.
Fatal cases of Legionnaires' disease have also been associated
with spa pool demonstrations.
What measures are there to control legionella?
To prevent exposure to the legionella bacteria, you as a
dutyholder must comply with legislation that requires you to
manage, maintain and treat water systems in your premises properly.
This will include, but not be limited to, appropriate water
treatment and cleaning regimes.
Remember, legionella can grow in any workplace if the conditions
are right - you do not have to work with microbiological agents, eg
in a laboratory, for exposure to occur. If you are responsible for
any of the water systems described in HSE's Approved Code of
Practice (ACoP) and Guidance "Legionnaires' disease: The
control of legionella bacteria in water systems" (L8) you
will need to assess the risk of employees and others in the
workplace contracting Legionnaires' disease.
Copies of L8 can be purchased from HSE Books. HSE also publishes
several free leaflets and a video explaining legal duties and the
control of legionella in cooling systems and hot/cold water systems
available from HSE Books.
Further information about Legionnaires' disease can be found on
the Health & Safety Executive (HSE) website.