Possibly there are too many inhibitors in respiratory specimens for a good sensitivity. The direct exams are useful if the specimen contains many organisms. Ordinarily a positive is more likely from a lung biopsy than from a sputum specimen. Antibody reagents to the genus Legionella are available and this test remains the most rapid, sensitive test to diagnose infection in a clinically useful time frame. Physicians should be encouraged to collect an invasive specimen.
Lung biopsy is the most sensitive specimen, if it can be obtained.
Specificity is high but cross reactions with fluorescing organisms, such a Pseudomonas can occur. The antisera has been reported to cross-react with other organisms, including Bordetella pertussis , which will grow on media for isolation of Legionella . The laboratory workup for Legionella should always include a culture. Both respiratory specimens and blood cultures have been successful in the diagnosis of legionellosis. The organism has been isolated from liver, spleen, pericardial fluid, kidney, and a variety of wound specimens for diseases that are extrapulmonary in nature.