# Establishing an external quality assurance scheme for the detection of Orientia tsutsugamushi IgM in clinical samples: Strengthening quality control of scrub typhus diagnosis in Indian laboratories

## TL;DR

This paper describes a quality assurance program to improve scrub typhus diagnosis in Indian labs by standardizing IgM antibody testing.

## Contribution

The study introduces and evaluates an external quality assurance scheme for scrub typhus IgM detection in Indian laboratories.

## Key findings

- Most participating laboratories showed consistent results in OTM testing.
- The EQA scheme highlights the importance of standardized protocols for infectious disease diagnostics.
- Regular quality assurance initiatives can improve diagnostic reliability and public health outcomes.

## Abstract

Scrub typhus, caused by Orientia tsutsugamushi, is a re-emerging zoonotic disease that is associated with significant morbidity and mortality in many parts of India. Early and accurate diagnosis, primarily through the detection of IgM antibodies, plays a pivotal role in patient management and disease surveillance. However, there is a paucity of diagnostic methods in our country, and only in recent years have more diagnostic assays been rolled out. To address the heterogeneity in the laboratory diagnosis of scrub typhus, an external quality assurance scheme (EQA Scheme) for the detection of O tsutsugamushi IgM (OTM) was conceptualized and implemented across a network of laboratories in India. This study provides detailed insight into the design, implementation, and outcomes of this EQA scheme initiative. Initially, a pilot phase was conducted among the 10 participant laboratories, and a total of 51 Virus Research and Diagnostic Laboratories (VRDLs) under DHR-ICMR undertaking OTM serology subsequently participated in the EQA Scheme. Proficiency testing (PT) panels consisting of 5 well-characterized and validated pooled serum samples were distributed to the participants for testing. Participating laboratories have employed various IgM detection methods, including ELISA and rapid immunochromatographic tests (ICTs). Performance was evaluated qualitatively based on the testing results and adherence to reporting timelines. Most laboratories demonstrated concordant results (n = 47) in OTM testing, while 4% of laboratories (n = 2) reported discordant results. The study underscores the vital role of an EQA scheme in ensuring quality-assured diagnostic testing for infectious diseases in the country and builds confidence in Indian laboratory results. Regular participation in such schemes, coupled with targeted capacity-building initiatives, can substantially improve laboratory diagnostics, facilitate timely clinical interventions, and contribute to a more robust national surveillance system. This model may serve as a foundation for strengthening quality assurance frameworks for other emerging infectious diseases in India and similar low- and middle-income settings.

Scrub typhus, caused by Orientia tsutsugamushi, is a major but underrecognized cause of acute febrile illness in many parts of India. Accurate laboratory diagnosis is critical for timely treatment and disease control. However, diagnostic performance can vary widely between laboratories due to differences in testing procedures, reagents, and quality control measures. To address this gap, we established an external quality assurance scheme (EQA Scheme) to assess and enhance the diagnostic capacity of Indian laboratories for detecting O. tsutsugamushi-specific IgM (OTM) antibodies. Our study involved the preparation and distribution of standardized, well-characterized serum panels to participating laboratories, followed by evaluation of their test results. We found considerable concordance in test performance across laboratories, highlighting the importance of standardized protocols and regular quality checks. This EQA Scheme initiative represents an important step toward improving the reliability and consistency of scrub typhus diagnosis in endemic regions. Strengthening diagnostic quality control will support better disease surveillance, patient care, and public health interventions in India and other tropical countries where scrub typhus remains a neglected threat.