Colonization of the respiratory tract with Legionella species.

Pneumonia is the most important manifestation of disease caused by Legionella species. However, it is still not known for certain how these organisms actually enter the lungs. During a 5-month period 318 hospitalized patients without clinical or radiologic features of pneumonia were enrolled in a survey of sputum colonization with Legionella. Diagnostic tests included cultures, direct fluorescent antibody test (DFA) and DNA probe assay of sputum. Colonization was considered to occur when at least one of these tests was positive. According to our definitions, 1.2-10% of of these patients could have been colonized by Legionella spp. However, all cultures were negative and in all but one of these patients the DFA was the only positive test. A case-control study comparing test-positive and test-negative patients failed to identify any different features of disease or epidemiologic characteristics. These findings suggest that a high rate of false-positive DFA results occurred in our study rather than any new evidence of colonization of the respiratory tract with Legionella.

Diagnostic efficacy of a DNA probe in pneumonia caused by Legionella species.

A commercial DNA probe kit (Gen-probe) for the detection of rRNA from legionellae was evaluated for its accuracy in diagnosing Legionnaires' disease in 167 patients with pneumonia. The test was performed on freshly obtained clinical respiratory tract samples. Cultures and direct immunofluorescence antibody (DFA) staining of the samples and serological tests were performed simultaneously for all patients. The probe assay result was positive in six patients; five of them had other laboratory evidence of disease (positive cultures or positive serological results or both). Depending on the diagnostic criteria, the probe test had a sensitivity of 31-67%, a specificity of 99% and positive predictive values of 67-83%. The diagnostic performance of the DNA probe assay in this study was superior to that of the DFA test. The results indicate that the examination of respiratory tract secretions by the Gen-probe kit is a suitable screening test for the diagnosis of Legionnaires' disease.

Legionella feeleii-associated pneumonia in humans.

Legionella feeleii has been implicated by serologic studies as the causative agent in an outbreak of Pontiac fever and has been recovered from an institutional water source. Pneumonia caused by this agent has not been described previously. The authors have isolated L. feeleii from two immunosuppressed patients with community-acquired pneumonia and from an institutional water source. One patient survived after treatment with erythromycin. The other patient was leukopenic and died of pneumonia. Isolates exhibited typical cultural and biochemical features of L. feeleii and reacted with L. feeleii serogroup 1 antiserum. L. feeleii serogroup 1 is now known to cause not only Pontiac fever but also pneumonia in humans.