Differentiation of recent and past infections with Legionella pneumophila by determination of specific IgM.

The ELA-IgM antibody test as used in viral diseases can also be applied to infections with Legionella pneumophila and is yielding similar results as the IgM determination by immunofluorescence. Complement-fixation and microagglutination are yielding also positive results in IgM-positive sera. IgM antibodies appear relative late after beginning of the disease and are persisting for several months. There is evidence that IgM antibodies as detected by the use of a Legionella pneumophila antigen are also cross-reacting to a number of other antigens.