Analysis on epidemiologic characteristics of severe fever with thrombocytopenia syndrome and influencing factors for case referral in Qingdao, Shandong, 2010−2023

Objective To understand the epidemiological characteristics and incidence trend of severe fever with thrombocytopenia syndrome (SFTS) and influencing factors for case referral in Qingdao, Shandong province, from 2010 to 2023, and provide evidence for the development of SFTS prevention and control strategies in Qingdao.

Methods The incidence data of SFTS reported in Qingdao from 2010 to 2023 were collected from China Disease Control and Prevention Information System for descriptive epidemiological analyses on the distributions of SFTS and changing trends. The interval between diagnosis and treatment and the influencing factors of the referral of SFTS cases during 2021−2023 were investigated by using Joinpoint regression model and logistic univariateate regression analysis.

Results From 2010 to 2023, a total of 495 cases of SFTS, including 26 fatal cases, were reported in Qingdao, in which 396 were confirmed cases and 99 were clinically diagnosed cases, with an annual average reported incidence rate of 0.38/100000 and the case fatality rate of 5.25%. The incidence of SFTS showed an obvious seasonality in Qingdao, with the incidence peak during April-October and 80.20% (397/495) of the cases occurring during this period. The male to female ratio of the cases was 1.09∶1. The overall number of reported SFTS cases showed an upward trend in Qingdao from 2010 to 2023 (annual percent change= 40.17%, P<0.01). Age odds ratio (OR) =0.57, P＜0.05 and the type of hospital for the initial visit (OR=12.23, P＜0.05) were influencing factors for referral. The lowest rate of referral was found in the cases who made the first visits to specialized hospital for infectious diseases.

Conclusion The overall incidence of SFTS showed an increasing trend in Qingdao. Huangdao district had the highest reported case count. Middle aged and elderly farmers were the population affected mostly. It is more difficult for primary medical care institution to make confirmation of SFTS, and it is necessary to transfer the cases to grade Ⅲ hospitals or hospitals specializing in infectious diseases. Therefore, health education should be carried out in key population to improve self-protection, and the professional l training of medical workers at all levels should be strengthened to improve SFTS diagnosis. The surveillance for ticks, animal host density and the pathogen carriage rate should be improved in priority areas, such as Huangdao district, and regular risk warning for SFTS needs to be made.