Legionellosis is an infection caused by the Legionella
pneumophila bacterium, which was first identified as recently as 1976, following
an outbreak of pneumonia at a convention of the American Legion in Philadelphia.
Legionellosis is occurs as Legionnaires' disease, a serious infection which
includes pneumonia, and Pontiac fever, a much milder illness.
is legionellosis usually found?
The Legionella bacteria occur naturally,
usually in water. The bacteria thrive in warm water, and are very much at home
in industrial-size air conditioning systems, cooling towers, hot water tanks,
and large pipe networks.
How common is legionellosis?
is an ubiquitous bacterium, a perennial threat to public health; occurrences of
Legionnaire's disease are sporadic but larger outbreaks can occur, such as those
related to tourist accommodations, from hotels to cruise ships.
is legionellosis transmitted?
Legionella is an opportunistic infection;
the bacterium survives readily in many water systems; high bacterial load might
be an important variable related to disease's occurrence in association to long-term
exposure; delivery via water vapour (eg in showers) appears to make infection
Can legionellosis be spread from person-to-person?
The amount of infection delivered into the atmosphere by an infected person does
not appear to present a real risk to others. Where outbreaks have occurred, only
a proportion of those at risk actually develop symptoms, suggesting that the body
can resist fairly high levels of droplet infection, in most cases.
possible to envisage a situation in which an immunosuppressed person who has prolonged
close contact with an infected person in a warm, damp environment might be at
some risk - but it's pretty unlikely, and there is no evidence of such an event
Who is most at risk from legionellosis?
people, smokers, and those living with a chronic lung condition do have an increased
As with all infections, people with damaged immune systems (eg due
to cancer, diabetes, or renal failure) are also more likely to become infected.
People who are immunosuppressed, (eg following organ transplant or cancer chemotherapy)
are also at increased risk.
What are the symptoms
People with Legionnaires' disease usually have fever,
chills, and a cough, which might be dry or might produce sputum. These symptoms
may be accompanied by muscle aches, headache, tiredness, loss of appetite, and
(occasionally) diarrhoea. Temperature may reach 39oC, and chest x-rays
will usually confirm pneumonia.
Persons with Pontiac fever, the non-pneumonic
form, present with an acute, self-limiting influenza-like illness. The incubation
period varies from a few hours up to a couple of days. The main symptoms are fever,
chills, headache, malaise and muscle pain. No deaths have been associated with
this type of infection, which usually resolves without treatment after 2 - 5 days.
are the long term effects of legionellosis?
is a serious illness, with a high mortality rate if not diagnosed and treated
rapidly. recovery can be slow, especially in older people, and long-term effects
may include pulmonary fibrosis and functional impairment of the lung.
is the mortality rate for legionellosis?
The mortality rate has been recorded
between five per cent and 30 per cent among those who have been treated, and as
high as 80 per cent in untreated patients.
is legionellosis diagnosed?
Many people become infected with the bacteria
with mild symptoms or no symptoms at all; so many cases may go undiagnosed.
examination and chest xray will suggest a diagnosis of pneumonia, but a specific
diagnosis must be confirmed in the laboratory by isolating the legionella bacteria
from sputum or other samples.
Is there a treatment
As with any serious respiratory infection, management
involves supoportive measures, which may include physiotherapy, oxygen and even
assisted respiration; specific treatment consists of antibiotics, which may depend
on the laborartory culture and sensitivity tests. Antibiotics used are usually
macrolides (for example, azithromycin) or quinolones (such as ciprofloxacin).
Tetracyclines may also be used. Erythromycin was initially the antibiotic of choice,
but has largely been replaced by more potent and less toxic antibiotics.
there a legionellosis vaccine?
There is no vaccine for legionellosis.
legionellosis be controlled environmentally?
Legionnaires' disease was
not identified until 1976; since then, extensive research has shown that it's
impact has been helped by the technology surrounding urban living.
that supports Legionella - or its spread - can include:
- Water features:
artificial fountains and water displays, such as those found in shopping centers,
restaurants and other modern buildings
- Cooling plant: industrial strength
air conditioning, climate control and refrigeration equipment, found at hospitals,
schools, hotels, office blocks ... any modern workplace.
- Car washes, particularly
those that use recirculated water, especially for rinsing.
- Showers: especially
communal, frequently used showers and those used over long periods with limited
- Industrial cleaning, particularly where rinsing or blowing
processes are involved.
- Humidification systems, including indoor growing
facilities, industrial sites such as paint booths.
In each case, the
processes described may accelerate Legionella pneumophila development,
aerosolization, or droplet spread.
Is there legal protection
for workers and others?
Now that the dangers of Legionella pneumophila
are known, there is a general duty of care by those responsible for such risks,
and is some countries, specific regulations to reduce the risks. Workers, authorized
visitors (eg swimming pool users), and the public (eg those walking beneath air
conditioning outlets) are entitled to a safe environment - or clear and specific
warnings of dangers.
Legal protection may include health and safety at work
laws, designation of dangerous substances or other laws, depending on the country.
Measures required or implied by law may include:
- Designing sytems such
that water is not undisturbed for long periods.
- Systems and water storage
facilities should be protected from contamination, and periodically inspected,
cleaned and disinfected.
- Water temperatures of 20oC to 45oC
should be avoided; hot water stored at or above at 60oC, circulating
at or above 50oC.
- Fittings and equipment in water systems should
be maintained as fit for purpose, using safe and reliable materials.
systems must be well designed, maintained and operated to prevent the escape of
fine water droplets.
- Water should be treated to prevent scale, corrosion
and microbial growth.
- Dry cooling systems, rather than cooling towers,
may be a safer option in many cases.
be learned from history?
The panic-led investigations into the Veteran's
outbreak of disease in Philadelphia eventually isolated the microbe, the investigation
involving more than a little luck. One factor in the delays was the assumption
that there was no such thing as an undiscovered bacterium; another that any bacteria
causing such havoc would thrive at or near human body temperature, rather than
much higher temperatures. Subsequest investigations proved that the disease was
by no means new, and once the chain of events was understood, valuable lessons
about urban living and its hazards were identified.
legionnaires' disease is not achievable, so vigilance combined with a balanced
response based on an understanding of costs and benefits is required" - Raj
S Bhopal, professor of public health.
and Further Information Sources
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Article written by Andrew Heenan BA (Hons), RGN, RMN