Incidence of Scrub Typhus in Rural South India

This population-based cohort study assessed the incidence and clinical spectrum of scrub typhus in 37 villages in Tamil Nadu, India, where the disease is endemic. Over 2 years, 32,279 participants were monitored for febrile illness, with blood samples collected during episodes. Among 6,175 fever episodes, 328 (7.3%) met the clinical case definition for scrub typhus (IgM seropositivity or PCR confirmation), yielding an incidence of 6.0 cases per 1,000 person-years. Severe illness (organ dysfunction or adverse pregnancy outcomes) occurred in 8.8% of cases (0.5 per 1,000 person-years), with a case-fatality risk of 1.5%. Serologic subcohort analysis revealed an asymptomatic seroconversion rate of 81.2 per 1,000 person-years. IgG seropositivity at baseline did not prevent clinical infection but was associated with milder disease. The study highlights scrub typhus as a significant cause of undifferentiated fever and hospitalization in endemic regions.

This population-based cohort study assessed the incidence and clinical spectrum of scrub typhus in 37 villages in Tamil Nadu, India, where the disease is endemic. Over 2 years, 32,279 participants were monitored for febrile illness, with blood samples collected during episodes. Among 6,175 fever episodes, 328 (7.3%) met the clinical case definition for scrub typhus (IgM seropositivity or PCR confirmation), yielding an incidence of 6.0 cases per 1,000 person-years. Severe illness (organ dysfunction or adverse pregnancy outcomes) occurred in 8.8% of cases (0.5 per 1,000 person-years), with a case-fatality risk of 1.5%. Serologic subcohort analysis revealed an asymptomatic seroconversion rate of 81.2 per 1,000 person-years. IgG seropositivity at baseline did not prevent clinical infection but was associated with milder disease. The study highlights scrub typhus as a significant cause of undifferentiated fever and hospitalization in endemic regions.