Determination of Region-Specific cut off value for Scrub Typhus IgM ELISA at a Tertiary Care Centre, Thanjavur, India

Rickettsial infections are primarily diagnosed using serological methods. The cut-off value for scrub typhus IgM ELISA is not standardized and varies depending on the disease prevalence in the geographical location where the kit is used. Therefore, establishing a region-specific cut-off value for diagnostic ELISA is crucial for the initial treatment of patients and distinguishing other febrile diseases in tertiary care settings. In this study, 300 patients from three different categories, including Category I (scrub typhus IgM ELISA positive patients), Category II (Dengue IgM ELISA positive patients), and Category III (100 healthy volunteers), were enrolled. Scrub typhus IgM ELISA (InBioS, International, Inc.) was performed, and the optical density (OD) values of all 300 samples were documented and analyzed using a receiver operating characteristic (ROC) curve. The analysis revealed a diagnostic IgM ELISA cut-off value of 0.728, with a sensitivity and specificity of 94% and 91%, respectively. Considering the significance of scrub typhus diagnosis for treatment and understanding disease dynamics in the Thanjavur district of Tamil Nadu, a cut-off value of >0.728 for diagnostic IgM ELISA can be utilized.