Status of serologic tests for Legionella antigen and antibody at the Centers for Disease Control.

Nine species and 16 serogroups have been defined for the genus Legionella. Direct immunofluorescence assay (DFA) results with 12 conjugates in 3 polyvalent pools showed that L. pneumophila serogroup 1 comprised 63% of the legionellae identified in specimens from patients with legionellosis. Indirect immunofluorescence assay (IFA) titers of paired sera from patients with suspected legionellosis against multiple Legionella antigens showed preferential reactivity for the L. pneumophila antigens. The multiple-antigen IFA was 96% specific when sera from patients with disease due to other etiologic agents were tested. The prevalence of antibody among well individuals is relatively high in some population groups.