SX | DX |
Organism: Legionella pneumophila, Legionella micdadei (Pittsburgh pneumonia
The Mode of Transmission: aspiration, aerosolization, or instillation
of water contaminated with Legionella into the respiratory tract.
Legionnaires's disease is pneumonia caused by Legionella species.
Fever, cough, blood streaked sputumi in about 10% of pts, chest pain,
pleuritic or nonpleuritic, in about 10% of pts, watery diarrhea, N&V,
abd. pain are seen in 25-50% of cases; headache & mental status
changes are the most common neurologic Sx.
Pontiac fever is an acute, self-limiting, flu-like illness caused
by Legionella species with 24-48 hours' incubation period & high attack
rate. Pneumm onia does not occur. The predominant Sx are malaise,
myalgias, fever, chills, & headache. Complete recovery is the rule
even without any specific therapy. It only requires symptomatic therapy;
no antibiotic therapy is required.
Chest x-ray initially shows a unilateral alveolar infiltrate, which
can progress to other lobes with consolidation. Diffuse interstitial infiltrates
were seen in 25% of those affected in 1976 outbreak. Radiologic improvement
lags behind clnical improvement.
Lab. findings: moderate leukocytosis, hyponatremia, small
gram-negative rods in Gram stain of sputum.
Isolation of the organism by culture from respiratory secretion is
the definitive method of diagnosis.
Direct fluorescent antibody stain of the specimen is rapid & highly
specific. Legionella antibody titers were often used in the past prior
to the advent of culture, but they require both acute & convalescent
serum. A single titer of 1:!28 is presumptive evidence of disease,
and a fourfold rise in titer is diagnosic. The sensitivity of serology
is about 40%.
Detection of Legionella Pneumophila-soluble antigens in urine is a
rapid diagnostic test that is highly sensitive. Antigen in urine is
detectable 3 days after the onset of clnical disease, even if specifc antibiotic
therapy is given, and it persists for several weeks.
Erythromycin 500 mg qid PO or 1 gm q6h
IV daily for 10-14 days, upto 3 weeks for immunosuppressed pts.
Combination of macrolide (erythromycin,
azithromycin, clarithromycin) or quinolone
(as Ciprofloxacin) with
rifampin as initial Rx in confirmed cases
of Legionnaires' disease.
Current Therapy in Adult Medicine 4th Ed, 1997 - Jerome Kassierer & Harry