One Health-based Joint Epidemiological Investigation of a Severe Fever with Thrombocytopenia Syndrome Case in the Republic of Korea, 2025.

OBJECTIVES: Following a healthcare-associated cluster of severe fever with thrombocytopenia syndrome (SFTS), a One Health-based joint epidemiological investigation integrating human, animal, and environmental components was conducted around the residence of the index patient to identify potential risk factors for infection and support the development of a standardized joint investigation framework. METHODS: Epidemiological investigations and family interviews were conducted to assess the patient's activities during the incubation period, including farming activities and history of contact with animals. Ticks were collected using dry ice-baited traps and flagging methods and tested for SFTS virus (SFTSV). Samples collected from a companion dog, stray cats, and water deer were analyzed using real-time reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and indirect immunofluorescent antibody assay. RESULTS: No SFTSV antigens or antibodies were detected in animal samples, suggesting that the case was unlikely to have resulted from animal-to-human transmission. A total of 341 Haemaphysalis longicornis ticks were collected, but all samples tested negative for SFTSV. Repeated vector control measures implemented after case identification may have affected vector density and test results. Epidemiological findings indicated frequent outdoor exposure during the incubation period, including gardening and walking along grassy rice-field banks. Although environmental and animal samples tested negative for SFTSV, the epidemiological findings suggested potential exposure to infected ticks. CONCLUSIONS: This investigation demonstrated the field applicability of a One Health-based joint epidemiological investigation integrating human, animal, and environmental surveillance. The findings highlighted the need for a multisectoral collaborative system and a standardized joint epidemiological investigation framework to strengthen future responses to zoonotic disease responses.