Escalating transmissibility of severe fever with thrombocytopenia syndrome in a high-endemic region of China.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging public health concern with increasing incidence and geographic spread. Quantitative assessment of its cross-species transmission among humans, ticks, and animal hosts remains limited. Here, we develop and apply a multi-population, multi-route dynamic model using data from 3,883 reported cases in Anhui Province, China, from 2019 to 2023 to quantify transmissibility and characterize spatiotemporal patterns. We estimate an average annual incidence of 1.3 per 100,000 and a case fatality rate of 3.1%. Cases are concentrated from April to September, and the transmission season extends into early spring and late autumn. Farmers and older adults are the main high-risk groups, and transmission risk is highest in central and southern Anhui. Model-based estimates indicate increasing transmissibility, with the basic reproduction number exceeding 1 from 2022 and reaching 1.5 in 2023; the highest prefecture-level estimate is 3.3 in Chuzhou. These findings show sustained expansion of SFTS transmission in a high-endemic region and support earlier, geographically targeted interventions for cross-species transmission control.