A Case of Aseptic Meningitis Caused by Leptospirosis in Gunma Prefecture, Japan.

We report a case of leptospiral meningitis in a 50-year-old man in Gunma, Japan, following contact with a rat carcass. Initially diagnosed with aseptic meningitis, cerebrospinal fluid (CSF) PCR identified Leptospira interrogans. The patient fully recovered after 7 days of intravenous ceftriaxone treatment. With 53 cases reported in Japan in 2024, continuing an upward trend since 2020, leptospirosis is an emerging etiology of acute febrile illness in Japan. Clinicians must maintain a high index of suspicion for leptospirosis in aseptic meningitis cases, reflecting the evolving epidemiology of this disease. Furthermore, clinicians should recognize the utility of CSF PCR testing in facilitating an early diagnosis.