Epidemiological investigation of an epidemic of severe fever with thrombocytopenia syndrome in a county in Hubei, 2023

Objective To understand the infection source, transmission routes of an epidemic of severe fever with thrombocytopenia syndrome (SFTS) in a county in Hubei province in August 2023, and put forward prevention and control recommendations.

Methods In this study, case definitions were developed for case finding, and then an epidemiological investigation was conducted, the basic characteristics, illness onset and hospital or clinic visits of the cases were described, and the infection source and transmission route were analyzed. Finally, tick density and virus carriage surveillance and serological test for healthy population were carried out.

Results Two cases were reported in this epidemic, i.e. 1 primary case (death) and 1 secondary case. Epidemiological investigation and analysis results showed that the first case might be bitten by environmental ticks, and the secondary case was infected due to contact with the first case's blood without protection, and case finding found no other associated cases. Tick density surveillance results showed that the mean density of free-living ticks was 16 ticks/(flag 100 m·h) and the density of dog-parasitic ticks was 9/host around the cases’ home, and all of the ticks were identified as Haemaphysalis longicornis, which were negative for specific nucleic acids of severe fever with thrombocytopenia syndrome virus (SFTSV). The results of serum antibody testing of 92 healthy persons showed that all of them were IgM negative, and 28 of them were IgG positive, with an IgG positive rate of 30.43%.

Conclusion This epidemic was the first family clustering of SFTS cases in the county. Local tick density and population antibody positive rate were high, suggesting SFTSV might being circulated in the local area. Therefore, SFTS surveillance and training in medical institutions should be further strengthened to improve the level of diagnosis and treatment. The health education about self-protection in population in key areas should be improved to reduce the risk for the transmission of the disease.