Six recent cases of severe fever with thrombocytopenia syndrome during the 2024 - 2025 in Kochi, Japan: A possible surge and clinical clue for early recognition.

Objectives: To characterize recent clinical features of severe fever with thrombocytopenia syndrome (SFTS) in an endemic region of Japan, emphasizing the importance of early clinical recognition. Methods: We retrospectively analyzed six consecutive adult patients with SFTS diagnosed at Kochi Health Science Center (Kochi, Japan) between 2024 and June 2025. Diagnosis was confirmed by real-time polymerase chain reaction testing, and viral load was quantified. Patient characteristics, animal exposure history, and laboratory findings were summarized. Results: Symptom onset occurred between March and November. Four patients had no tick bite marks, while three had recent cat exposure. All patients exhibited thrombocytopenia, elevated liver enzymes, and a slight elevation of serum C-reactive protein. Favipiravir was administered in all cases, with five recoveries. One patient developed hemophagocytic syndrome despite a moderate viral load. Conclusions: In endemic and warm-climate regions, SFTS should be suspected year-round. Key clinical features, including cat exposure, thrombocytopenia, and a slight elevation of serum C-reactive protein, may aid early diagnosis even in the absence of tick bite history.