Legionnaire's disease
Clinical clues suggestive of Legionnaire's disease:
Diarrhea
High fever (>40°C; >104°F)
Numerous neutrophils but no organisms seen by Gram's staining of respiratory secretions.
Hyponatremia (serum sodium <131 mg/dL)
Failure to respond to beta-lactam drugs (PCN or cephalosporins) and aminoglycoside Abx
Occurrence of illness in an environment in which the potable water supply is known to be contaminated with Legionella
Onset of symptoms within 10 days after discharge from the hospital.
Microbiology:
L. pneumophilia causes 80 - 90% of human infections
serogroups 1, 4, and 6 are most commonly implicated in human infections.
Aerobic gram-negative bacilli. Atypical as it does not grow on routine microbiologic media. Buffered charcoal yeast extract (BCYE) agar is the medium needed to grow legionella.
DFA (direct fluorescent antibody) test used to definitively identify the organism.