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. 2023 Jun;157(6):519-523.
doi: 10.4103/ijmr.IJMR_4098_20.

Determination of a cut-off value for the serological diagnosis of scrub typhus by detecting anti- Orientia tsutsugamushi immunoglobulin M

Amita Jain  1 , Parul Jain  1 , Sanjay C Rebello  1 , Moulika Todaria  1 , Harmanmeet Kaur  2 , Nivedita Gupta  2 , Neeraj Aggarwal  2 , Neetu Vijay  3 , Jitendra Narayan  3
Affiliations

Determination of a cut-off value for the serological diagnosis of scrub typhus by detecting anti- Orientia tsutsugamushi immunoglobulin M

Amita Jain et al. Indian J Med Res. 2023 Jun.

Abstract

Background & objectives: The 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.

Methods: Samples 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.

Results: Anti-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 & conclusions: The cut-off calculated for India was similar to the previous cut-off that was used until now.

Keywords: Enzyme-linked immunosorbent assay cut-off; Orientia tsutsugamushi; immunoglobulin M; indirect immunofluorescence assay; scrub typhus.

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Conflict of interest statement

None.

Figures

Fig. 1
Fig. 1
Images of immunoglobulin M indirect immunofluorescence assay (x 400 magnification).
Fig. 2
Fig. 2
ROC curve analysis for estimation of cut-off. ROC, receiver operating characteristic; ELISA, enzyme-linked immunosorbent assay; OD, optical density.
See this image and copyright information in PMC

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