[Biological diagnosis of Legionnaire's disease].

Specific laboratory diagnosis of Legionnaires' disease is possible using sputum and other respiratory tract samples. Culture diagnosis, overlooked in the past, should now be the major means of laboratory diagnosis. Detection of bacterial antigen in respiratory secretions and urine by immunologic means has the advantage of speed of diagnosis (hours vs. days for culture diagnosis), but the disadvantage of the need for use of many different antibody types. Serological diagnosis, by detection of antibody changes, probably has the lowest specificity of any of the specific tests, and often takes weeks rather than days or hours to make a diagnosis of Legionnaires' disease.