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Legionella
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Legionnaire disease was first described
in1976 after an outbreak of fatal
pneumonia in Philadelphia at an American Legion reunion held in
a convention.
The newly described organism thatcaused the disease was named Legionella
pneumophila.
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Morphology
L.pneumophila.
Gram negative rods.
Stains poorly by gram stain(carbol
fuchsin).
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Culture
Buffered charcoal yeast extract agar (BCYE).
Aerobe,PH 6.9,temperature 35c.
humidity 90%.
Growth is slow .
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Legionella on BCYE
Slowly growing bacteria after 3 days
incubation.
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Biochemical characters
Catalase positive.
Oxidase positive.
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Antigenic structure
There are more than 10 serogroups.
The original Philadelphia strain
serogroup1,is still the most common.
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Mode of infection Inhalation of aerosols carrying the bacteria
from warm moist sources.
(air conditioning system & shower heads)
Its not transmitted from patient to others.
L.pneumophila enters and grows within
alveolar macrophages , followed by lysis .
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Pathogenesis
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Pathogenesis Legionella are found in warm moist
environments.
Envionmental reservoir;protozoaincludingamoeba.
Asymptomatic infection is common.
The incidence of clinically significantdisease is high in the old,debilitated&immunocompromised persons.
Atypical pneumonia.
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Immunity Just as intracellular multiplication is
the key to L.pneumophila virulence ,its
inhibition by cell mediatedmechanismsappear to be the most important aspect
of immunity.
The peak antibody response may notoccur until 4-8 weeks after infection.
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Laboratory diagnosis
Specimens:bronchial washings,pleuralfluid, lung biopsy or blood.
Smears: microcopic examinationofdirect fluorescent antibody staining of
specimen.
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L.pneumophila
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Laboratory diagnosis
Culture:BCYE agar.
Identification:by immunofluorescentstaining.
Serology: levels of antibodies tolegionella rise slowly during the illness.
Serological tests are useful in a
retrospective diagnosis in outbreaks oflegionella infections.
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Treatment &control
Erythromycin,the treatment of choice.
Cleaning, chlorination & heating of
water can help to control themultiplication of legionellae in water
and air conditioning systems.
Not communicable disease
