EVALUATION OF CLINICAL USEFULNESS OF THE MICROPLATE AGGLUTINATION-TEST FOR SEROLOGICAL DIAGNOSIS OF LEGIONELLA-PNEUMONIA

Recently, a microplate agglutination test (MPAT) was established for t he serological diagnosis of legionella pneumonia. To evaluate its usef ulness, this study examined antibody titres in 121 serum samples seria lly obtained from 40 patients with pneumonia, including 17 cases of co nfirmed legionella pneumonia. Six of the 17 proven cases became serolo gically positive within 4 weeks of the onset of pneumonia as assayed b y MPAT (cut-off value: four-fold rise to greater than or equal to 128 in paired sera or greater than or equal to 256 in a single serum speci men), whereas the remaining 11 cases were serologically negative despi te serial examination. Four proven cases who were treated with cortico steroids in the acute phase had antibody titres <8 during the first 4 weeks of infection, after which one case showed an elevation in antibo dy titre for the first time, 13 weeks after the onset of disease. In c ontrast, all non-proven cases had antibody titres of less than or equa l to 64, and only one case developed a four-fold or greater rise in ti tre. These results indicate that MPAT is a useful method for the labor atory diagnosis of suspected legionella pneumonia, although several fa lse-negative cases were observed. This suggests that the previously es tablished MPAT criteria may require modification, possibly to slightly lower values. These data also indicate that serial examination over t he first month of infection may be necessary for serodiagnosis of legi onella pneumonia, especially in patients treated with corticosteroids.