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.