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Legionnaires
disease is a disease caused by the organism LEGIONELLA
PNEUMOPHILA, which is found naturally in water
and soil where it is normally harmless. However,
when it gets the right conditions of temperature,
nutrient supply and pH, it multiplies rapidly,
and if there is aerosol formation and a susceptible
population, these are all the ingredients for
an outbreak.
In
1976 an outbreak of pneumonia occurred in members
of the American Legion (an ex-servicemen's organisation)
attending a conference at the Belview Stratford
Hotel in Philadelphia. Of 192 diagnosed cases,
20 were fatal. Examinations of lung tissue from
some of the fatal cases demonstrated the presence
of a previously unknown organism which was eventually
called LEGIONELLA PNEUMOPHILA. Retrospective
studies have since shown that some earlier outbreaks
of severe pneumonia of unknown cause were, in
fact, due to infection with Legionella.
Although
there are at least 44 species of legionellae,
L. Pneumophila is by far the most important human
pathogen.
Legionnaires
Disease mainly affects adults, with men being
more at risk than women. The greatest incidence
of disease is in men over 50 years of age who
also smoke. Persons who are immuno-compromised
or suffering from respiratory disorders are also
at higher risk. Infection is by inhalation of
contaminated water droplets.
If
antibiotic therapy of the appropriate kind is
not applied soon after diagnosis, significant
mortality can result.
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