Internal Medicine

0521779407-10 CUNY1086/Karliner 0 521 77940 7 June 6, 2007 17:44

888 Legionella Infections

■Pontiac fever is an acute self-limited disease characterized by fever,

malaise, myalgias and headache without pneumonia; complete

recovery in 1 week, even without therapy, is the rule.

tests

■Chest x-ray abnormalities nonspecific; early infiltrates usually in

lower lobes and alveoli, but can be patchy and diffuse and can

progress to lobar consolidation; nodular densities with cavitation

more common in the immunocompromised, as are interstitial infil-

trates; pleural effusions (usually small) in up to one third

■Laboratory abnormalities nonspecific except hyponatremia

(sodium <130 mEq/ml), which is more common in Legionella

pneumonia than pneumonia caused by other agents; normal or

elevated WBC, abnormal liver function tests, hypophosphatemia all

described

■Gram stain of sputum or other sterile fluid usually shows many poly-

morphonuclear leukocytes with few or no Gram-negative organisms

(Legionella stain poorly, are small and thus difficult to see on Gram

stain)

■Culture of sputum is the gold standard & positive in 80% (slightly

higher with bronchoalveolar lavage). Direct fluorescent antibody test

on sputum is rapid, but sensitivity only 30–70%. Urinary antigen test

rapid, sensitive (70–80%) but only detects L. pneumophila serogroup

1 and can remain positive for months. Serum antibody testing lim-

ited by slow rise in antibody titers (6–12 weeks); a single titer of 1:128

suggestive of infection, but 4-fold rise is required to document infec-

tion. PCR available, but not more sensitive than culture.

differential diagnosis

■Other causes of pneumonia due to S. pneumoniae, H. influenzae,

Mycoplasma pneumoniae, Chlamydia pneumonia, Chlamydia psi-

tiaci, etc.

management

■General supportive care with supplemental oxygen, fluids and pres-

sors, if indicated

specific therapy

■Newer macrolides (azithromycin, clarithromycin) or fluoro-

quinolones (ciprofloxacin IV, levofloxacin) are first-line drugs.

Some observational studies suggest that levofloxacin is superior to