Surveillance for sever fever with thrombocytopenia syndrome in Henan province, 2017-2020

Abstract

Objective: To analyze the epidemiological and etiological characteristics of sever fever with thrombocytopenia syndrome (SFTS) cases in Henan province during 2017-2020. Methods: Descriptive epidemiology method was used to analyze the characteristics of SFTS cases in Henan during 2017-2020. Patients' sera in acute phase were collected and tested using real-time fluorescence RT-PCR. The S segment complete sequences of the isolated sever fever with thrombocytopenia syndrome virus (SFTSV) strains were amplified and homology analysis was performed to construct the phylogenetic tree. Results: A total of 1 767 SFTS cases, including 1 000 suspected cases and 767 confirmed cases, were reported in Henan during this period, and 11 cases, including 3 suspected cases and 8 confirmed cases died, the case fatality rate was 0.62% (11/1 767). The incidence decreased year by year. The cases were distributed in 28 counties of 6 cities, and 1 681 cases were reported in Xinyang, accounting for 95.13% (1 681/1 767) of the total. The cases mainly occurred from April to October, accounting for 96.10% (1 698/1 767) of the total. The incidence in males (0.38/100 000) was significantly lower than that in females (0.54/100 000) (χ2=54.855, P<0.001). Up to 93.44% (1 651/1 767) of the cases were aged between 40 and 84 years. Farmers accounted for 96.10% (1 698/1 767) of the total cases. One family cluster outbreak occurred in 4 years. A total of 1 110 samples were detected by Henan CDC, in which 435 were SFTS virus positive with an average positive rate of 39.19% (435/1 110). The differences in positive rates of SFTS virus among different years were significant (χ2=25.405, P<0.001). The sequence homology of complete S segment of the 39 SFTS virus strains ranged from 94.76% to 99.82%. The genetic evolution analysis on the complete S segment of the 39 SFTS virus strains showed that 34 strains belonged to genotype A, 2 strains belonged to genotype B, and 3 strains belonged to genotype D. Conclusions: The incidence of SFTS in Henan was sporadic, and decreased year by year. SFTS had obvious regional and seasonal characteristics, and the area affected by SFTS expanded. The incidence of SFTS was high in elderly female farmers, and the positive rate of SFTS virus varied greatly in different years. The main type of SFTS virus in Henan was genotype A, but the etiological surveillance is still needed.