Comparison of microagglutination with the indirect immunofluorescence assay for the diagnosis of infection with Legionella pneumophila serogroup 1.

A comparison was made of the indirect immunofluorescence assay and microagglutination in the diagnosis of infections caused by Legionella pneumophila serogroup 1. Control sera consisted of 709 sera from patients without pneumonia and 99 sera from patients with Mycoplasma or Chlamydia infection. The 468 test sera were from 51 patients with serologically confirmed or suspected Legionella pneumophila serogroup 1 infection, and from 230 patients with pneumonia of unknown aetiology. There was good agreement between the results of the two methods for detection of antibodies to Legionella pneumophila serogroup 1. However, contrary to what is currently reported in the literature, microagglutination was the more sensitive method in this study, especially if the first serum samples were compared. The detection of IgM by microagglutination probably explains this increased sensitivity.