Epidemiology of Lyme disease, a growing tick-borne disease of concern, in Japan from May 2013 to March 2024: a descriptive study.

Objectives: Lyme disease (LD) is a globally distributed zoonosis; however, limited epidemiological data are available from Japan. This study aimed to elucidate the characteristics of LD cases reported through the Japanese national surveillance system. Methods: We conducted a retrospective descriptive study based on data from the National Epidemiological Surveillance of Infectious Diseases for the fiscal years 2006-2023. Results: Overall, 265 LD cases were reported, ranging from five in 2008 to 28 in 2023 (median: 12.5), including 216 domestic, predominantly from Hokkaido, and 43 imported cases. The median annual notification rate for domestic cases was 0.94 per 10 million population (range: 0.39-2.14). The median age was 53 years, and 62% were male. No fatal cases were reported. Most infections occurred between May and September. Common clinical features of the cases included erythema migrans, fever, and neurological symptoms. The median duration from onset to diagnosis was 28.5 days (interquartile range: 16-45 days). Conclusions: The number of LD cases in Japan has increased, with cases predominantly occurring in middle-aged men from Hokkaido and other areas. Furthermore, patients having LD presented with non-specific symptoms, including neurological involvement, resulting in delayed diagnoses. These findings highlight the importance of increasing awareness of LD in Japan.