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Legionnaires'
disease (Legionellosis)
is an acute bacterial infection, caused by Legionella pneumophila (a
minute, gram-negative
bacillus),
which involves primarily the lower respiratory tract, although it is
often associated with multi-systemic extrapulmonary manifestations.
Afflicted patients may sometimes have gastrointestinal symptoms, liver
function abnormalities, renal failure , central nervous system
complications and cutaneous manifestations which may include
erythematous, maculopapular or petechial skin lesions.
About 6 months after an
outbreak of a severe respiratory disease of unknown cause at the
American Legion’s state convention in Philadelphia in 1976, L. pneumophila was identified by workers at the Centers for Disease
Control.
Subsequently, retrospective serologic and immunoflourescent
studies revealed antibodies in sera from previously unexplained
epidemics.
Of historical note is the first epidemic so recognized, in
a meat packing plant in
Minnesota in 1957.
Legionnaires’ disease occurs sporadically, as epidemics, and as nosocomial infections, especially in patients with compromised
immunity.
Those who abuse alcohol and smoke heavily are also at
increased risk.
The organism has been recovered from
soils, ponds, water systems, and air conditioning systems.
Legionellosis has been recognized throughout the world,
without a geographic pattern.
The disease
presents as a rapidly progressive, severe, necrotizing pneumonia, accompanied by fever,
nonproductive cough, and myalgias.
The onset is abrupt, after an
incubation period of 2 to 10 days.
Within 2 days, most patients
develop a persistent high fever and respiratory rales.
Radiograms of
the chest reveal unilateral, diffuse, patchy broncho- pneumonia,
progressing to widespread nodular consolidation, usually without cavitation.
Visit:
Pulmonary Infection
;
Pneumocystis Pneumonia
;
Bronchopneumonia
Toxic symptoms and hypoxia may be prominent,
and death may follow in a few days.
In those who survive, convalescence is
prolonged.
The antibiotic of choice is
erythromycin.
The main changes
in the lung include consolidation, necrosis, and acute congestion.
Microscopically, the alveoli are packed with an exudate composed of histiocytes and fibrin.
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The alveolar walls become necrotic and are
destroyed.
Neutrophils accumulate as necrosis becomes more pronounced
and eventually confluent.
Many histiocytes show eccentric nuclei,
pushed aside by cytoplasmic vacuoles containing L . pneumophila.
Dissemination of L . pneumophila to the kidneys, spleen, bone marrow,
and lymph nodes has been reported.
Isolation and
identification of the bacilli is necessary for an unequivocal
diagnosis, but isolation may be hazardous.
The direct fluorescence
antibody test for L . pneumophila can be performed on formalin-fixed,
paraffin-embedded tissue and is thus valuable for conforming the
diagnosis.
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