Application of Enzyme Linked Immunosorbent Assay (ELISA) and Indirect Fluorescent Antibody Test for Serodiagnosis of Acute Scrub Typhus in and Around Puducherry, India

摘要

Scrub Typhus (ST) is now endemic in India and is diagnosed by Immunochromatography based rapid kits or conventional ELISA to detect IgM antibodies. Clinical picture of ST may mimic other diseases like Dengue, Leptospirosis and viral haemorrhagic fevers. Indirect Fluorescent Antibody Test/Immunofluorescence assay (IFA) is the reference standard which might help to confirm ST.Aim: To critically analyse the practical utility of the gold standard IFA vis-à-vis ELISA in identifying acute ST in patients.Materials and Methods: Archived acute blood samples from 140 febrile patients with clinical suspicion of acute ST, 70 patients with other febrile illnesses and 70 voluntary healthy blood donors were subjected to both ST IgM ELISA and ST IgM IFA. Statistical Analysis: Chi-Square test was applied and p-values =0.05 were considered statistically significant.Results: IgM IFA was positive in 120 out of 140 ST IgM ELISA positive ST patients and 16 out of 70 ST IgM ELISA negative febrile patients. All 70 blood donors were negative in both IgM ELISA and IgM IFA. Against the gold standard IFA, Sensitivity, Specificity, Positive Predictive value and Negative Predictive values for IgM ELISA were 88.24%, 86.11%, 85.71%, 88.57% respectively. Titres of =1:64 were considered as significant for IgM IFA.Conclusion: It is recommended that standardisation is required regarding significant cut-off titre for IgM IFA in different regions of India. For serodiagnosis of acute ST, IgM ELISA still remains.