The diagnosis of Legionnaires’ disease depends on positively identifying the organism, preferably by culture or molecular methods. A number of clinical and laboratory findings may help to identify a patient who is more likely to have the disease.
Patient selection: signs and symptoms of pneumonia with new infiltrate on chest X-ray
Clinical findings:
(1) fever (temperature > 39°C)
(2) confusion or other neurologic impairment
(3) diarrhea
(4) failure to respond to initial antibiotic therapy
Laboratory findings:
(1) hyponatremia (< 131 mmol/L)
(2) hypophosphatemia
(3) abnormal liver function tests not explained by underlying conditions
(4) elevated serum creatinine
(5) elevated serum CK associated with rhabdomyolysis
(6) hematuria
(7) sputum with leukocytes AND (no organisms or Gram-negative bacteria not growing on routine culture)
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