Diagnosis of legionellosis by microagglutination test--comparison to indirect immunofluorescent antibody method

We studied the micro-agglutination method (MAT) for the diagnosis of legionellosis. Serum samples were collected from 44 clinically legionellosis suspected patients (17 positive with indirect immunofluorescent antibody technique [IFA] and 27 IFA negatives) and 20 healthy adults (25-30 years old). MAT showed negative results with sera collected from healthy adults and IFA negative patients, 8 out of 17 cass of IFA positive patients showed positive results in MAT. The remaining 9 cases out of 17 were negative in MAT judging from our criteria (1:256 in single serum or fourfold rise to 1:128 in pair sera). MAT had good proportion to IFA in samples collected within three weeks after onset of each disease. All sera that became positive in MAT were sampled within four weeks after onset of each illness. It was noted that MAT was mainly related to IgM-class antibodies. These relationships must be decided by investigating more cases of legionellosis. According to the result of this study, the MAT method was thought to be useful for rapid diagnosis of legionellosis.