Seroconversion of Indirect Immunofluorescent Antibody IgM and IgG in Melioidosis

Background: There are several serological tests used in the diagnosis of melioidosis. However, the interpretation of the results can be problematic in endemic areas because there might be a high background positivity due to previous exposure. Objective: This study aimed to determine the usefulness of Indirect Immunofluorescent Antibody (IFA) IgM and IgG in the diagnosis of melioidosis and the time for seroconversion. Methodology: We prospectively studied the trend of IFA IgM and IgG in 40 patients with culture-confirmed melioidosis over three months at six different time points (days 1, 8, 15, 30, 60, and 90). Results: From the results, 37.5% and 32.5% of patients had IFA IgM and IgG of ≤ 1:20 respectively on day 1 when the blood culture was positive. The natural log (ln) of the titres was used for the analysis. Repeated measures ANOVA showed significant changes in both IgM (p= 0.001) and IgG (p= 0.045) respectively throughout six sampling time points. Both the means of ln IgM and ln IgG peaked at day 15. At day 90, mean ln IgG remained high but mean ln IgM dropped to a level below that of day one. All culture-confirmed melioidosis patients recorded a maximum IFA IgM titre of at least 1: 80, but all subsequently dropped to below this level at day 90. Conclusion: IFA IgM is a more useful diagnostic serological marker than IFA IgG in acute melioidosis. Bangladesh Journal of Infectious Diseases 2020;7(2):61-66