Comparison of a micro-agglutination test and the indirect immunofluorescence test for Legionella antibodies in patients.

A micro-agglutination (MA) test for antibodies to 10 different Legionella antigens was compared with the indirect immunofluorescence (IF) test. The antigens used were prepared from Legionella (L.) pneumophila serogroups (SG) 1-6, L. micdadei, L.bozemanii, L.dumoffii, and L.gormanii. Sera from 728 patients suspected of suffering from Legionella pneumonia were investigated by both tests. Thirty-five patients showed a significant rise in IF titre to greater than or equal to 128, and 43 had single or static titres of greater than or equal to 256 while the remaining 150 had negative IF titres. The results of the comparison indicate that the MA test offers at least the same sensitivity as the IF test in demonstrating diagnostic titre rises. It may be used as a screening test for selection of sera for further analysis by the IF test. In contrast to the IF test, MA is simple and inexpensive.