Application of indirect hemagglutination test and indirect fluorescent antibody test for IgM antibody for diagnosis of melioidosis in Thailand

Abstract

In hyperendemic areas such as Thailand, rapid diagnosis of melioidosis depends upon both bacteriological culture and serological methods. However, interpretation of indirect hemagglutination (IHA) for melioidosis which is the only test available, is seriously hampered by increased IHA titers present in one-third to one-half of the population. In order to get the best results from the available tests, IHA and indirect fluorescent antibody for IgM (IFA-IgM) were evaluated in controls and patients in Thailand. IHA titers of ≥ 1:40 were considered remote or recent exposure to P. pseudomallei. IHA titers of this level were found in 47.1% of 227 blood donors and 29.5% of 210 sera submitted for other tests, while IFA-IgM was positive in only one donor who had an IHA titer of 1:1,280. IHA was positive in eight out of nine patients with melioidosis with IHA titers of < 1:20 to 1:2,560. IFA-IgM was positive in six out of seven melioidosis patients whose sera were available for this test including a serum with IHA titer of < 1:20. Six patients were predisposed by diabetes mellitus. Among sera serologically tested for melioidosis, 33 had IHA titers of 1:80-1:1,280, 10 of which were positive for IFA-IgM. This study demonstrates high background IHA titers among Thai people which greatly limits its use for serodiagnosis of melioidosis. In sharp contrast, serodiagnosis by IFA-IgM was more successful. Positive IFA-IgM among healthy Thais did exist indicating that serologic tests for melioidosis at best are only supplementary to bacteriological culture and clinical awareness.