[Microbiological diagnosis of Legionnaires' disease]

Besides other bacterial genera legionellae are a major causative agent of severe pneumonia. Therefore, it is essential to include legionnaires' disease into the diagnostics of pneumonia of unknown origin. The appreciable number of different species and serogroups of legionellaceae, most of them pathogenic for humans, render this task more difficult. The cultural isolation of legionellae from patient or environmental samples is easily performed, the identification of the isolates may be difficult, however. Structural features of the bacteria as determined by biochemical techniques may support the usual immunological identification. Now as before the serological determination of the patients' antibody production as well as the direct detection of bacteria by immunofluorescence microscopy are basic diagnostic procedures. In addition, it is possible to test for legionella antigens excreted in patients' urines; the diagnostic value of this assay, however, is dependent on the manufacturer of the system. As well the clinical diagnostic efficiency of a commercial nucleic acid probe has been questioned sometimes. In the future the polymerase chain reaction may prove as a valuable diagnostic tool but the ubiquity of legionellae in aquatic habitats requires a very critical evaluation of this high-sensitivity method.