• Amita Jain, Parul Jain, Sanjay C Rebello, Moulika Todaria, Harmanmeet Kaur, Nivedita Gupta, Neeraj Aggarwal, Neetu Vijay, and Jitendra Narayan.
• Department of Microbiology, King George's Medical University, Lucknow, Uttar Pradesh, India.
• Indian J Med Res. 2023 Jun 1; 157 (6): 519523519-523.

Background & ObjectivesThe diagnosis of scrub typhus (ST) is usually done using enzyme-linked immunosorbent assay (ELISA) due to its ease of performance and reading objectivity. The cut-off value for ELISA needs to be calculated for each geographical location as it depends on zonal endemicity of the disease. This study was, therefore, undertaken to calculate the pan-India cut-off for anti-Orientia tsutsugamushi (OT) immunoglobulin M (IgM) by ELISA.MethodsSamples from cases (cases of ST) and controls (voluntary, consenting, healthy adults) were collected by a network of 29 laboratories across India and tested for anti-OT IgM by immunofluorescence assay (IFA), the considered gold standard test. These samples were retested by ELISA for anti-OT IgM and their optical densities (ODs) were used for cut-off estimation by receiver operating characteristic (ROC) curve.ResultsAnti-OT IgM ELISA ODs from 273 controls and 136 cases were used for the cut-off estimation. The ODs of the anti-OT IgM ELISA on healthy individuals and those of confirmed ST cases ranged from 0.1 to 0.75 and 0.5 to 4.718, respectively. ROC curve-based cut-off for ELISA was calculated as 0.554 at a sensitivity of 95.2 per cent and specificity of 95.1 per cent. A value of >1 was noted to have a specificity of 100 per cent in diagnosing ST.Interpretation & ConclusionsThe cut-off calculated for India was similar to the previous cut-off that was used until now.

15 keywords...

hide…