Prevalence of anti-Legionella antibodies in a healthy population and in patients with tuberculosis or pneumonia.

The prevalence of antibodies to 13 antigens of Legionellaceae were compared in three populations: 583 blood donors, 140 tuberculosis patients and 66 patients with acute non Legionellosis pneumonia. Antibody levels were determined by indirect immunofluorescence (IFA) using formalized antigens prepared from bacteria developed in embryonated hen yolk sac. The very weak prevalence of anti L. pneumophila antibodies in a healthy population [almost nil for serogroups 2, 3, 4 and 5; 1.5% for serogroup 6, maximum of 2.5% for serogroup 1 (titres of 16)] confirms the positive and presumptive criteria that have been recommended by Centers for Disease Control (CDC). But as regards the other Legionellae studied, these criteria cannot be applied owing to the prevalences that are higher in healthy populations (until 14.5% with levels of 16-32 and 1% with levels of 64-128 for L. bozemanii) and clearly amplified in tuberculosis patients and in acute pneumonia. Although the significance of these antibodies remains to be discussed, with formalized antigens, it seems reasonable as regards these species to assign a threshold of 256 for the presumptive and positive criteria following seroconversion.