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

TL;DR

The paper reports six recent SFTS cases in Japan, highlighting clinical clues like cat exposure and lab markers for early diagnosis.

Contribution

The study identifies cat exposure and specific lab findings as potential early indicators of SFTS, even without tick bite evidence.

Findings

SFTS occurred year-round in Kochi, Japan, with symptom onset between March and November.

Clinical features included thrombocytopenia, elevated transaminases, and slight C-reactive protein elevation.

Favipiravir treatment led to recovery in five out of six patients, despite one developing hemophagocytic syndrome.

Abstract

•Severe fever with thrombocytopenia syndrome (SFTS) occurs year-round in warm regions.•History of cat exposure may help in the clinical diagnosis of SFTS.•Absence of visible tick bites does not rule out SFTS.•SFTS presents with thrombocytopenia, elevated transaminases, and a slight elevation of C-reactive protein.

Severe fever with thrombocytopenia syndrome (SFTS) occurs year-round in warm regions.

History of cat exposure may help in the clinical diagnosis of SFTS.

Absence of visible tick bites does not rule out SFTS.

SFTS presents with thrombocytopenia, elevated transaminases, and a slight elevation of C-reactive protein.

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.

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.

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.

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.