Scrub Typhus Outbreak at Sagalee Block, Arunachal Pradesh, India, September 2023

In August 2023, a scrub typhus "outbreak-alert" was generated by the Integrated Disease Surveillance Program from Sagalee block, Arunachal Pradesh, India.

We investigated to characterize the outbreak and identify possible exposures.

A case was defined as immunoglobulin M antibody positive for scrub typhus by rapid diagnostic or enzyme-linked immunosorbent assay in resident (>6 months stay) of Sagalee block between January and September 2023 and identified from surveillance line-list and facility record review. We interviewed cases using a semi-structured questionnaire for demographics, clinical presentations, and possible exposures. We surveyed the case environment for shrubs, water bodies, domestic animals, and rodent infestation. We collected rodent pinna for mite isolation and serology samples for the Weil-Felix test and calculated entomological indices.

Of 42 cases identified (67% females, median age 40 years, interquartile range 28-50), 83% were farmers and 62% had forest-dependent livelihoods. Eschar was present in 12% cases; 98% recovered, and one died. All cases resided either within 100 m of forest, fields, and water bodies or 10 m from bushes, 95% reported domestic or peridomestic rodent activity, and none used insect repellent or insecticide/rodenticide. Rodent infestation rate was 78% (18/23), chigger-index nine (207/23) (critical value 0.69), and 44% (7/16) of rodent samples had significant (>1:40) OXK titres in Weil-Felix test.

We demonstrated that conducive ecology, favorable human host behavior, and high density of vector infestation completed the epidemiological triad of scrub typhus. We recommended that the district heath unit to coordinate with the agricultural and allied departments for rodent control activities and community awareness for personal protection measures.