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Year : 2021  |  Volume : 23  |  Issue : 1  |  Page : 9-13

Enzyme-linked immunosorbent assay as a substitute for immunofluorescence assay: An analysis of different serological tests in diagnosis of scrub typhus

1 Department of Microbiology, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh, Uttar Pradesh, India
2 Department of Microbiology and Immunology, College of Medicine and Health Sciences, Sultan Qaboos University Hospital, Muscat, Oman

Correspondence Address:
Dr. Asfia Sultan
Department of Microbiology, J.N Medical College, Aligarh Muslim University, Aligarh, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jacm.jacm_41_21

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BACKGROUND: Among the causes of acute febrile illness, scrub typhus is an important entity. Serology is the mainstay of diagnosis of scrub typhus, with immunoglobulin M (IgM) immunofluorescence assay (IFA) test being the gold standard. Because of cost constraint, IFA cannot be employed for screening or routine diagnosis. This study was planned to evaluate the diagnostic efficacy of different serological test available for Scrub typhus. MATERIALS AND METHODS: Total of 414 cases of undiagnosed acute febrile illness of >5 days were evaluated for scrub typhus. The tests employed were Weil-Felix, rapid immunochromatographic test, IgM enzyme-linked immunosorbent assay (ELISA) and IgM IFA. Performance of all the tests was evaluated against gold standard IFA test by IBM SPSS version 20.0 (SPSS Inc. Chicago, USA) and MedCalcsoftware. RESULTS: Total of 112 (27%) were positive by ELISA while 32 (7.7%) and 44 (10.6%) cases were positive by Weil-Felix and RDT, respectively. Of these, only 98 (23.6%) samples showed titre of ≥1:64 by IFA. Statistical analysis showed sensitivity and specificity of IgM ELISA, 100 (95% confidence intervals [CI]: 96.31–97.88) and 96.05 (95% CI: 93.34–97.88) respectively. The sensitivity and specificity of RDT and Weil Felix was 64.47 (95% CI: 56.31–72.06) and 57.65 (95% CI: 49.85–65.18) and 100% (95% CI: 98.84–100) and 98.14 (95.99–99.31), respectively. On analysis of association between OD values and IFA titres, Spearman correlation coefficient was 0.783 (P < 0.01) while Pearson correlation coefficient r2 = 0.879(P < 0.01). Youden's index of Weil-Felix, RDT and ELISA was 0.56, 0.64 and 0.96, respectively. CONCLUSION: IgM ELISA has turned out to be a significant tool in diagnosis of scrub typhus.

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