Analysis Of Epidemiological Characteristics And Influencing Factors Of Severe Fever With Thrombocytopenia Syndrome In Shandong Province

Background:Severe fever with thrombocytopenia syndrome(SFTS)is an emerging tick-borne infectious disease caused by a novel bunyavirus.SFTS is mainly transmitted to humans through the bite of infected ticks and there is no specific vaccine to prevent SFTS.In recent years,clusters of SFTS with high fatality rate have attracted wide attention from the whole society.Currently,SFTS is mainly distributed in China,South Korea,Japan and other places in Asia,and China has the highest incidence of it.Shandong Province is one of the major epidemic areas of SFTS.After 2021,the number of reported cases in Shandong Province has climbed to the first place,and the case fatality rate is higher than the national average.It has become an important part of infectious disease emergency management in Shandong Province to clarify the epidemic characteristics and influencing factors of SFTS,adopt effective prevention and control measures,and further improve the prevention and control level and response ability of SFTS.A number of studies have shown that the occurrence of SFTS is related to meteorological and geographical factors,including temperature,precipitation,relative humidity,sunshine duration,altitude and slope.At the same time,the epidemiological characteristics and diffusion patterns of SFTS show significant differences among clusters in different regions,suggesting that the occurrence and spread of SFTS may have spatial heterogeneity.At present,a variety of methods have been developed and applied in the field of epidemiology.However,most studies on SFTS are limited to the description of surveillance data or global analysis,and the spatial heterogeneity of their effects is not taken into consideration.Spatial regression model is widely used in the field of spatial epidemiological statistics,and local regression performs well in quantifying the spatial characteristics of disease epidemics.Considering the differences in the effects of influencing factors in time and space dimensions,it can help us effectively identify the influencing factors related to SFTS and quantify the direction and size of their effects,so as to formulate regional prevention and control measures,and finally effectively control and reduce the incidence of SFTS.Objectives:1.The epidemiological characteristics of SFTS in various districts and counties in Shandong Province were analyzed in order to find the high-risk areas,high incidence seasons and high risk populations.2.Explore the spatial distribution of SFTS in Shandong Province,analyze the influence of meteorological,geographical and population economic factors on the incidence of SFTS,and reveal the spatial differences of their effects,so as to provide scientific evidence for the formulation of specific prevention and control measures in each region.Methods:The data of SFTS cases reported from January 1,2016 to December 31,2020 in Shandong Province and the data of environmental variables and population economics variables in the same period were collected to obtain the annual index values of districts and counties.The incidence of SFTS in Shandong Province during the study period was described and its epidemic was summarized.By means of trend analysis and spatial autocorrelation analysis,the spatial character of SFTS distribution and its spatial dependence and heterogeneity which identify the local clustering areas of SFTS incidence were investigated.Modeling was carried out from three perspectives,including static global regression analysis,static local regression analysis and dynamic local regression analysis.Evaluation indexes such as coefficient of determination(R2),adjusted coefficient of determination(adj.R2)and akaike information criterion(AIC)were used to compare the models and select the optimal model of each part to comprehensively analyze the influence of environmental and population economic factors on the incidence of SFTS.Combined with geographic information system,the local regression coefficients were displayed on the map to reveal the spatial differences between the influencing factors and the incidence of SFTS.Results:1.From 2016 to 2020,a total of 3,111 SFTS cases were reported in Shandong Province,with the annual reported incidence ranging from 0.51/100,000 to 0.73/100,000.The cases in Yantai,Jinan and Weihai accounted for 60.79%of the total cases in the province,and the cumulative incidence in Wendeng District,Mengyin County and Rongcheng City ranked the top three.Most of the cases were concentrated from May to October,accounting for 95.92%of the total number of cases.The incidence peaked in Yantai,Weihai and Weifang Cities in June,Zibo and Linyi in August,and Jinan,Tai’an,Rizhao and Qingdao Cites had two peaks.80.01%of the cases were in(50,80]age group,and the median age of onset increased year by year.The male to female incidence rate ratio was 1:1.06,because the number of female cases was higher than that of male cases in May-June and(50,70]age group.Farmers were the most important occupational group,accounting for 86.53%of the total.2.Trend analysis showed that the incidence of SFTS showed an upward trend from west to east,and a weak inverted U-shape from north to south.Spatial autocorrelation analysis showed spatial correlation and heterogeneity in the distribution of SFTS in Shandong Province.The global Moran’s I values were all greater than 0,and the P values were all less than 0.01.The incidence of SFTS in each district and county showed a spatial positive correlation in the province.The results of local autocorrelation analysis indicated that the high-high aggregation areas were mainly distributed in the eastern peninsula,the southern part of Jinan City and the eastern part of Tai’an City.3.After Spearman correlation analysis,annual mean temperature,annual accumulated precipitation,annual relative humidity,annual mean wind speed,normalized vegetation index,altitude,and night light index were included for spatial regression analysis.The results of static global regression showed that annual mean temperature and altitude significantly affected the incidence of SFTS,but not statistically significant during these years.Static local regression manifested that multiscale geographically weighted regression(MGWR)significantly improved the model fitting degree compared with ordinary least squares(OLS)and geographically weighted regression(GWR).The local R2 in GWR were between 0.289 and 0.481,while these in MGWR were between 0.354 and 0.573.The annual mean temperature,altitude and night light index were tested to be statistically significant.The bandwidth of annual mean temperature and altitude were small,which had a great influence on local areas.The annual mean temperature showed a stable negative effect in the peninsula region over the five years.The regression coefficients of altitude are mostly positive,with lower in the eastern counties and higher in the inland counties.The dynamic local regression showed that the R2 of geographically and temporally weighted regression(GTWR),GWR and time-weighted regression(TWR)models increased by 82.13%,77.17%and 8.89%compared with OLS model,respectively.The annual mean temperature,altitude and normalized vegetation index passed the statistical test of temporal and spatial changes,and the absolute value of the regression coefficient of altitude was the largest,which contributed the most to the incidence of SFTS in Shandong Province.The effect of altitude and annual mean temperature on the peninsula area was the strongest,and the effect increases gradually from Qingdao to Yantai and Weihai,and the positive effect was the most significant in Linyi City.Conclusions:1.In Shandong Province,SFTS occurred most frequently in eastern Shandong Peninsula and surrounding areas of central Shandong Province,mainly in middle-aged and elderly farmers,with obvious seasonal distribution pattern and regional differences.The incidence peak was earlier in the peninsula region than in the inland region.2.The incidence of SFTS was higher in the eastern part of Shandong Province than in the western,and higher in the central than in the southern and northern.The annual high incidence clustering in the peninsula area was obvious and tended to be stable.3.Altitude and annual mean temperature were the most important factors affecting the incidence of SFTS in Shandong Province,and the direction,magnitude and scale of their effect had obvious spatial differences.The relevant departments should strengthen the disease surveillance when the temperature is low in the peninsula area,high in the central area of Shandong Province,and in the areas adjacent to the hills and plains.