Detection of Scrub Typhus Antibodies by Serological Tests and Their Comparative Evaluation for Validation of Serological Testing
Ujjwala Dehankar, Neena Nagdeo, Rajesh Dehankar, Janaki RajaramanAbstract
Background:
Scrub typhus has emerged as a significant cause of acute febrile illness in India, with increased morbidity when diagnosis is delayed. Its nonspecific clinical presentation and limited availability of advanced diagnostic facilities pose challenges in timely identification. Although the indirect immunofluorescence assay is the reference standard, it is not widely accessible in resource-limited settings, necessitating the use of rapid and reliable diagnostic tests.
Objective:
The objective of this study was to evaluate the diagnostic performance of a rapid immunochromatographic test (RICT) for scrub typhus and compare it with immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA).
Materials and Methods:
This prospective study was conducted at a tertiary care hospital in Central India and included 120 clinically suspected cases. Serum samples were tested using the SD Bioline Tsutsugamushi rapid test and IgM ELISA (J.Mitra and Co.), with ELISA considered the reference standard. Sensitivity, specificity, predictive values, and diagnostic accuracy were calculated. Receiver operating characteristic (ROC) curve analysis was performed.
Results:
Of the 120 samples, 52 (43.3%) were positive by ELISA and 49 (40%) by the rapid test. Eschar was present in 19% of patients. The rapid test showed sensitivity of 98%, specificity of 95.7%, positive predictive value of 94.2%, and negative predictive value of 98.5%, with an overall accuracy of 96.7%. The area under the ROC curve was 0.96.
Conclusion:
The RICT is a reliable, rapid, and cost-effective tool for early diagnosis of scrub typhus in resource-limited settings, though clinical correlation remains essential.