# Comparative Analysis of Scrub Typhus Rapid Kits and Their Relevance in Screening and Diagnosis

## TL;DR

This study compares rapid diagnostic tests for scrub typhus, finding they are effective for early detection in resource-limited areas.

## Contribution

The study evaluates and compares the performance of three rapid diagnostic tests for scrub typhus using ELISA as a reference.

## Key findings

- RDTs showed high IgM sensitivity (89.60%–96.80%) and specificity (84.00%–98.29%) for scrub typhus detection.
- IgG detection had lower sensitivity (51.06%–74.47%) compared to IgM.
- Clinical parameters like bilirubin and protein levels differed significantly between positive and negative cases.

## Abstract

Background: Rapid diagnostic tests (RDTs) are increasingly recognized as practical tools for the early detection of infectious diseases, particularly in resource-limited settings. These tests offer the advantage of portability, ease of use, and quick turnaround times, making them ideal for point-of-care diagnostics. This study evaluates the diagnostic performance of three commercially available RDTs for scrub typhus, using IgM and IgG enzyme-linked immunosorbent assays (ELISAs) as reference standards, to assess their reliability and applicability in clinical and field settings.

Methods: A cross-sectional study was conducted at the Kalinga Institute of Medical Sciences, Eastern India, over one year. Serum samples from 300 clinically suspected scrub typhus cases were tested using three RDTs, with IgM and IgG ELISAs as reference tests. Diagnostic accuracy metrics, such as sensitivity and specificity, were calculated. Statistical analysis compared results across RDTs.

Results: Of the 300 samples, 125 (41.67%) tested positive for scrub typhus by ELISA. For IgM detection, sensitivities ranged from 89.60% to 96.80% and specificities from 84.00% to 98.29%. For IgG, sensitivities ranged from 51.06% to 74.47% and specificities from 82.21% to 94.47%. The differences in diagnostic performance among RDTs were statistically significant (P < 0.05). Clinical parameters indicated significant differences in direct bilirubin, total protein, albumin-to-globulin (A:G) ratio, and potassium levels between the scrub typhus-positive and negative groups.

Conclusions: This research is important and applicable, considering the widespread occurrence of scrub typhus in India and the demand for easy-to-use diagnostic tools in areas with limited resources. It confirms that RDTs are a practical, IgM-based tool for early scrub typhus detection owing to their ease of use and portability, suiting point-of-care needs, but quality control and validation are crucial. Positive correlation with inflammatory markers further underscores its utility as a diagnostic tool. Further multicenter, longitudinal, and cost-effectiveness studies are needed to support their wider adoption in national programs.