Scrub typhus linked to high disease burden in rural India

1. In this cohort study, scrub typhus was a common cause of febrile illness in rural South India, with an incidence of 6.0 cases per 1000 person-years.

2. Asymptomatic infection was widespread, with a high seroconversion rate indicating significant underrecognized disease burden.

Evidence Rating Level: 2 (Good)

Study Rundown: Scrub typhus, caused by the mite-born bacteria Orientia tsutsugamushi, is a significant cause of undifferentiated fever across South and Southeast Asia. This population-based cohort study assessed the burden of scrub typhus in rural South India, identifying it as a significant cause of febrile illness. Many cases led to hospitalization, and severe complications were observed, particularly among older adults and individuals with diabetes. A high rate of asymptomatic infection indicated that scrub typhus is likely underrecognized in endemic areas. The study’s large sample size and systematic follow-up provided strong epidemiologic data, but potential underreporting due to COVID-19 restrictions and reliance on serologic testing were notable limitations. The study highlights that scrub typhus is a significant cause of febrile illness in endemic areas, often requiring hospitalization. Delayed diagnosis and a lack of awareness hinder treatment despite the availability of effective antibiotic options.

Click here to read the study in NEJM

In-Depth [prospective cohort]: This population-based cohort study was conducted over two years in rural Tamil Nadu, India, where scrub typhus is endemic. The study enrolled 32,279 participants, tracking febrile illnesses through regular household visits every six to eight weeks. Blood samples were collected for serological and molecular testing to confirm Orientia tsutsugamushi infections. Among the 4,474 blood samples collected, 328 met the criteria for scrub typhus diagnosis based on IgM ELISA positivity, qPCR detection, or eschar presence. Of these cases, 21.6% required hospitalization, with an incidence of 1.3 cases per 1000 person-years (95% Confidence Interval [CI], 1.0 to 1.7). Additionally, 8.8% of cases were classified as severe, occurring at a rate of 0.5 cases per 1000 person-years (CI, 0.4 to 0.8). The case fatality rate was 1.5%, with five confirmed deaths attributed to the infection. The study also included a serologic subcohort of 2128 participants to assess asymptomatic infections. The incidence of seroconversion was 81.2 per 1000 person-years (CI, 70.8 to 91.6), with older individuals showing higher seroprevalence and infection rates. While IgG positivity was associated with reduced severity of illness, it did not prevent reinfection, emphasizing the need for further preventive measures. Older individuals and women exhibited higher infection rates, though severity levels remained consistent across genders. Past infection did not provide full immunity, reinforcing the potential for reinfection. The findings underscore the necessity for increased surveillance, improved diagnostic efforts, and the development of preventative strategies.

Image: PD

©2025 2 Minute Medicine, Inc. All rights reserved. No works may be reproduced without expressed written consent from 2 Minute Medicine, Inc. Inquire about licensing here. No article should be construed as medical advice and is not intended as such by the authors or by 2 Minute Medicine, Inc.