First autochthonous case of severe fever with thrombocytopenia syndrome in Hokkaido, the northernmost island of Japan.

We identified a patient with severe fever with thrombocytopenia syndrome (SFTS) in Hokkaido, the northernmost island of Japan, where no SFTS cases had previously been reported. The patient developed fever, thrombocytopenia, transient neurological symptoms, and concomitant Escherichia coli bacteremia following a suspected tick bite and subsequently recovered. The patient had no travel history to known SFTS-endemic areas, suggesting local acquisition of infection. SFTS virus (SFTSV) infection was confirmed by reverse transcription-polymerase chain reaction, virus isolation, and serologic analysis. Phylogenetic analysis suggested that the isolate may not be assignable to any previously recognized clade. These findings support local acquisition of SFTSV infection in Hokkaido and highlight the importance of expanding surveillance and diagnostic preparedness for emerging tick-borne diseases beyond currently recognized endemic areas.