Assessment of two immunoassays for detection of IgM antibodies to scrub typhus using a serum panel

Laboratory tests are necessary for diagnosis of scrub typhus (ST) especially in the absence of the distinctive eschar. Performance of an ELISA and ICT (immunochromatography) to detect IgM antibodies to scrub typhus was assessed using a panel of 346 sera chosen from healthy individuals, those with scrub typhus and scrub-typhus like illness. A sensitivity of 98.7% for ST IgM ICT and 97.4% for ST IgM ELISA was observed while specificity was 96.3% for ICT and 95.9% for ELISA. As excellent concordance (98.8%) was noted between the two assays, IgM ICT can be used for rapid diagnosis of scrub typhus. Abbreviations: ST IgM ELISA: Scrub typhus IgM ELISA; ST IgM ICT: Scrub Typhus IgM Immunochromatography, Rapid diagnostic test: RDT.