The diagnosis of Legionnaires' disease by counterimmunoelectrophoresis.

Counterimmunoelectrophoresis (CIE) was found to be a rapid, specific method for detecting circulating antibodies to Legionella pneumophila, the aetiologic agent of Legionnaires' disease in human sera. Optimum conditions for performing the test are given. Better precipitin lines are observed when the gel support is neutral, and a result may be obtained in 90 to 180 minutes. Comparison of results of CIE and indirect fluorescent antibody tests on 22 sera from patients with Legionnaires' disease and on 27 sera from healthy control subjects showed 100% correlation, and 75 paired sera from patients with pneumonia of unknown aetiology showed 96.7% correlation. Laboratory diagnosis may be made quickly and accurately by CIE. The method is simple and easily performed in the routine laboratory. The antigen is stable at 4 degrees C for at least six months.