Comparison of Commercial Enzyme-Linked Immunosorbent Assay and Immunofluorescence Assay for Diagnosis of Acute <i>Rickettsia typhi</i> Infections

Abstract

Murine typhus is a tropical disease caused by Rickettsia typhi and is endemic in resource-limited settings such as Southeast Asian countries. Early diagnosis of R. typhi infection facilitates appropriate management and reduces the risk of severe disease. However, molecular detection of R. typhi in blood is insensitive due to low rickettsemia. Furthermore, the gold standard of sero-diagnosis by immunofluorescence assay (IFA) is cumbersome, subjective, impractical, and unavailable in many endemic areas. In an attempt to identify a practical diagnostic approach that can be applied in Indonesia, we evaluated the performance of commercial R. typhi IgM and IgG enzyme-linked immunosorbent assay (ELISA) and IFA using paired plasma from previously studied R. typhi PCR-positive cases and controls with other known infections. Sensitivity and specificity of combined ELISA IgM and IgG anti- R. typhi using paired specimens were excellent (95.0% and 98.3%, respectively), comparable to combined IFA IgM and IgG (97.5% and 100%, respectively); sensitivity of ELISA IgM from acute specimens only was poor (45.0%), but specificity was excellent (98.3%). IFA IgM was more sensitive (77.5%), but less specific (89.7%) for single specimens.