Comparative evaluation of serological and molecular methods for the diagnosis of scrub typhus in Indian settings

The major brunt of scrub typhus is borne by developing countries like India but the disease remains neglected. The rapid progression of this infection to serious complications and associated mortality calls for improved diagnostics. The immunoglobulin (Ig)M immunofluorescence assay (IFA), with all of its limitations remains the gold standard. Of 218 suspected cases from patients enrolled in a 2-year study, 30 cases of scrub typhus were detected by IgM IFA, using a 1:64 dilution. The sensitivities of the IgM enzyme-linked immunosorbent assay, IgM rapid flow assay (RFA), and IgG RFA were found to be 97z, 87z, and 77z, respectively. Their respective specificities were 100z, 100z, and 92z, respectively. The sensitivity and specificity of a nested PCR assay targeting a gene encoding a 56-kDa protein were found to be 50z and 100z, respectively.