Severe Fever With Thrombocytopenia Syndrome / Tick Borne Disease · Journal article

Meteorological and environmental factors associated with the spatiotemporal risk of severe fever with thrombocytopenia syndrome in Japan: A prefecture-level time-series modeling study.

One Health · August 14, 2026

Promising Why this matters to you Expert discussion

Encouraging direction, but not yet definitive.

AI Summary

This prefecture-level time-series analysis of 1237 SFTS cases identifies meteorological and environmental factors—temperature, precipitation, atmospheric pressure, forest coverage, and altitude—associated with SFTS transmission risk in Japan, with specific risk thresholds quantified. The findings are observational and require independent validation, but provide actionable targets for public health surveillance and preparedness.

What was studied

Nationwide prefecture-level time-series analysis with generalized additive mixed model. All SFTS cases reported via national surveillance in Japan from March 2013 to December 2025, analysed at the prefecture level.. n = 1,237. Japan; all 47 prefectures..

Key findings

Mean temperature showed inverted U-shaped association with peak SFTS risk at 21.8 °C (RR: 1.78, 95% CI: 1.26–2.52) Precipitation peak risk at 156.6 mm (RR: 1.30, 95% CI: 1.04–1.62) Atmospheric pressure positively associated with maximum RR of 2.06 (95% CI: 1.44–2.93) at 1027.1 hPa

Safety

Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.

Who this may help

Clinicians and public health officials should use these identified environmental thresholds to anticipate SFTS outbreaks and focus prevention campaigns—particularly in forested, low-altitude prefectures during warm, moderately rainy seasons. However, these associations should be confirmed in other geographic settings before informing high-stakes policy changes.

Plain-language summary

A rigorous prefecture-level time-series analysis with a large national dataset and adjustment for confounders, identifying specific meteorological and environmental thresholds for SFTS risk, but based on observational data without a comparator intervention and requiring replication.

Study design

As stated by the source record.

MethodsWeekly SFTS surveillance data from all 47 prefectures in Japan (March 2013–December 2025) were analysed using a generalized additive mixed model adjusting for nonlinear seasonality and long-term trends. Meteorological (temperature, precipitation, atmospheric pressure), environmental (forest coverage, altitude), and demographic factors were assessed for associations with SFTS risk. Inverted U-shaped and monotonic associations were identified, and the factor values yielding maximum relative risk were estimated.

DesignNationwide prefecture-level time-series analysis with generalized additive mixed model

PopulationAll SFTS cases reported via national surveillance in Japan from March 2013 to December 2025, analysed at the prefecture level.

Sample size1,237

SettingJapan; all 47 prefectures.

Reported figures

Quoted from the source exactly as published.

Total SFTS cases1237

Temperature peak RR1.78

Temperature peak RR 95% CI1.26–2.52

Temperature threshold21.8 °C

Precipitation peak RR1.30

Precipitation peak RR 95% CI1.04–1.62

Precipitation threshold156.6 mm

Atmospheric pressure peak RR2.06

Clinical bottom line

Caveats

Observational study; cannot establish causation or exclude unmeasured confounding (e.g., behavioral changes, healthcare-seeking patterns, tick surveillance effort by prefecture).
Surveillance data quality and reporting variation across prefectures not discussed; misclassification and underreporting may bias results.
Threshold estimates are specific to Japan's geography and surveillance system; generalizability to other countries or regions unclear.
No validation cohort or independent replication presented; model fit and predictive accuracy not reported.

Evidence assessment

Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.

Study design

strong

Nationwide prefecture-level time-series with generalized additive mixed model; nonlinear seasonality and trends adjusted.

Directness

strong

Examines actual SFTS surveillance cases and environmental exposures across Japan over 12 years.

Consistency

moderate

Single study; associations plausible (temperature, precipitation, forest coverage influence tick ecology) but no independent replication reported.

Risk of bias

moderate

Observational design; surveillance data subject to reporting variation across prefectures; no discussion of unmeasured confounding.

Sample adequacy

strong

1237 cases across 47 prefectures over 156 weeks; large geographic and temporal range supports estimation of nonlinear thresholds.

Source abstract

Background. Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonotic disease with a high case fatality rate and expanding geographic distribution in Japan. Comprehensive evaluations that integrate meteorological, environmental, and demographic factors remain limited. This study aimed to quantify these associations.Methods. We conducted a nationwide prefecture-level time-series analysis using weekly SFTS surveillance data in Japan from March 2013 to December 2025. A generalized additive mixed model adjusting for nonlinear seasonality and long-term trends was used to assess (1) the associations between SFTS risk and meteorological, environmental and demographic factors, and (2) the value of the factor at which risk become highest.Results. A total of 1237 SFTS cases were reported. Mean temperature and precipitation showed inverted U-shaped associations with SFTS risk, with peak risks observed at 21.8 °C (relative risk [RR]: 1.78, 95% confidence interval [CI]: 1.26-2.52) and 156.6 mm (RR: 1.30, 95% CI: 1.04-1.62), respectively. Atmospheric pressure and forest coverage were positively associated with SFTS risk, with maximum RRs of 2.06 (95% CI: 1.44-2.93) at 1027.1 hPa and 6.58 (95% CI: 4.95-8.74) at 0.84, respectively. Mean altitude showed an inverse association, with the highest RR observed at 45.0 m (RR: 3.99, 95% CI: 1.81-8.76).Conclusions. The increasing number and geographic expansion of SFTS cases highlight the growing public health importance of this disease in Japan. Our findings improve understanding of factors associated with SFTS transmission and may inform future risk assessment and public health preparedness.

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Fangyu YanNoriko KitamuraSevere Fever With Thrombocytopenia SyndromeTick Borne DiseaseYu TakizawaDaisuke YoneokaTaro KamigakiSophearen Ith