Comprehensive epidemiological analysis of severe fever with thrombocytopenia syndrome in Japan, 2013-2023: descriptive observational study.

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne zoonotic disease that poses a serious public health challenge in several Asian countries. In this study, we aimed to describe the recent epidemiological characteristics of SFTS in Japan using denominator-based test data.

METHODS

We analysed reported SFTS case-patients in Japan using national surveillance data from March 2013 to April 2024. The case-fatality ratio (CFR) was calculated using the National Vital Statistics Surveillance System (NVSSS) for 2013-2022. Trends in test numbers and positivity rates were examined using data from annual reports and public health institute surveys.

FINDINGS: During the study period, 931 case-patients were reported, including 11 veterinary healthcare workers. The annual notification rate rose from 3.12 per ten million in 2013 to 10.46 in 2023, with 30 (64%) estimated infection prefectures, primarily in western and central Japan. The NVSSS CFRs remained high at approximately 20%. Test numbers and positive results increased from 2013 (n = 350, n = 41) to 2022 (n = 923, n = 95); however, positivity decreased from 12% to 10%.

INTERPRETATION: The annual SFTS notification rate increased, and infection regions expanded between 2013 and 2023, with persistently high CFRs and increased testing. Veterinary healthcare workers appear to be a potential high-risk group. These findings highlight that SFTS remains a public health concern in Japan, requiring a comprehensive health strategy.

FUNDING: This work was supported by the Japan Society for the Promotion of Science Kakenhi Grants-in-Aid for Young Scientists (grant number: 24K19277).