Although pneumonia is present in nearly all patients with Legionnaires' disease, extrathoracic symptoms can be the presenting or predominant features. Central nervous system, gastrointestinal, and renal manifestations are especially common. L. pneumophila has been isolated from blood cultures, and the organism can be found in many organs in both immunosuppressed patients and in previously normal patients who are afflicted with severe disease. A nonpneumonic form of legionellosis called Pontiac fever has a short incubation period and a low mortality. It has been responsible for at least four outbreaks of illness, including several related to whirlpools and hot tubs.
Cold agglutinins are negative.
Other laboratory findings may include elevated erythrocyte sedimentation rate, abnormal liver function test results, and hypoxia. Proteinuria and microscopic hematuria have been observed, and acute renal failure may complicate the course on occasion. Gram's stains of the sputum or tracheal secretions fail to reveal L. pneumophila . A kit that uses radiolabeled complementary DNA is commercially available, but clinical experience is still limited. A PCR assay is being developed.