Objective To understand the epidemiological characteristics of severe fever with thrombocytopenia syndrome （SFTS）， and the association with seasonal fluctuation in tick density， so as to provide scientific evidence for better control and prevention measures.
Methods Descriptive epidemiological methods were used to analyze the SFTS epidemic situation in Chongyang County from 2013 to 2021. The cloth flag method was used to investigate the seasonal fluctuation in tick density and determine the association with the SFTS.
Results A total of 71 SFTS cases were reported in Chongyang County from 2013 to 2021 including 8 deaths， with the annual morbidity rate of 1.88/10-5. The majority were mainly from June to August， accounting for 61.97% of the total reported cases. The cases were geographically distributed in 41 administrative villages and 4 urban areas in 11 towns. The highest incidence was in Lukou town （n=26） and Baini town （n=12）， which accounted for 53.52% of the total reported cases. Furthermore， the cases were mainly 50‒69 years old， accounting for 57.75% of the total reported cases. The ratio of male to female was 1.84∶1， and most were farmers. Blood samples during acute phase in 41 cases were collected for examination of SFTS virus， of which 25 cases tested positive （60.98%）. There was a positive association between tick density and the number of reported SFTS cases （r=0.78， P=0.003）.
Conclusion Seasonal density of free adult ticks and nymphs is associated with the number of reported SFTS cases in Chongyang County.
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