Study On The Epidemiological Characteristics And Temporal-spatial Analysis Of Bacillary Dysentery In The Three Gorges Area

Objective:1.To describe the epidemiological characteristics and trends of bacillary dysentery in the Three Gorges Area,and compare the differences of characteristics of the disease between the counties in three gorges reservoir area(counties of the TGRA)and counties in non-three gorges reservoir area(counties of the non-TGRA).2.To investigate the spatial and temporal distribution patterns and hot spot areas of bacillary dysentery in the Three Gorges Area,and to analyze the relationship between outbreaks of bacillary dysentery and spatial-temporal clusters.Method:The incidence data of bacillary dysentery and the epidemic reports of bacillary dysentery outbreaks in the Three Gorges Area from January 1,2005 to December 31,2016 were obtained from National Notifiable Infectious Disease Reporting System and National Public Health Emergency Reporting Information System.The demographic data were collected from the Statistical Yearbook of Chongqing and Hubei respectively and the Sixth National Census in 2010,and carried out the following studies:1.Comparing the incidence of bacillary dysentery in the Three Gorges Area from 2005 to 2016 with the national scale,and describing the time,space and regional distribution characteristics of the cases;using the annual reported morbidity and the monthly cases to describe the long-term trend and seasonality of bacillary dysentery,Extract the age,sex and occupation information of the case and describe the population distribution characteristics of the case;Make thematic maps to visually demonstrate the incidence level and regional distribution characteristics of each county(district)by using ArcGIS.2.Use ArcGIS to establish spatial correlation between spatial data and case data to establish a GIS database of cases.Use GeoDa to explore the spatial clustering of the bacillary dysentery in the Three Gorges Area by using global and local spatial autocorrelation.With the aid of spatial-temporal scanning statistics(SaTScan)to study the spatio-temporal distribution characteristics of disease,determine the spatio-temporal clustering area of it.Combined with outbreak information to understand the hot spots area of bacillary dysentery,and analyze the relationship between the epidemic outbreak and spatial-temporal clusters.3.According to the patient's county and the current address of the national standard in the case information,the cases were divided into cases of the TGRA and cases of the non-TGRA.Then analyze and compared the similarities and differences of their epidemiologic characteristics.Results:1.In 2005-2016,126 138 cases of bacillary dysentery were reported locally in the Three Gorges Area.The reported incidence rate was between 20.84/100 000 and 39.36/100 000,and the average incidence rate(28.93/100 000)was 1.49 times that of the whole country(19.38/100 000).The bacillary dysentery showed a fluctuating downward trend,and the national average annual decline rate(11.68%)was 2.48 times faster than that of the Three Gorges Area(4.71%).2.Cases of bacillary dysentery occurred all the year round with a seasonal distribution.The peak incidence is concentrated from May to October each year,peaking in August.Sex ratio of cases is 1.18:1,0?4 age group had the most cases accounting for 45.53%and the highest incidence(241.95/100 000).The incidence rate of elderly people aged 70 and over had a gradually increasing trend,while other age groups all fluctuate at lower levels.Cases were dominated by scattered children(41.96%),followed by farmers(14.02%)and students(10.99%).The annual average incidence rate of 61 counties(districts)is quite different,with obvious spatial heterogeneity.The high incidence areas were Chengkou county in the north of Chongqing,Yuzhong,Dadukou,Jiangbei,Shapingba,Jiulongpo,Nanan,Yubei District in Chongqing urban areas and the main urban districts of Yichang(Xiling and Wujiagang),with an average annual incidence between 60.20/100 000 and 114.81/100 000.3.The overall incidence level of bacillary dysentery in the counties of the TGRA is higher than the counties of the non-TGRA.84 661 cases and 12 deaths were reported in counties of the TGRA.41 477 cases and 9 deaths were reported in counties of the non-TGRA from 2005 to 2016.The average incidence rate of the TGRA(36.63/100 000)was 1.81 times that of the non-TGRA(20.20/100 000).The average annual decline rate of the non-TGRA(6.48%)was 1.59 times faster than that of the TGRA(4.07%),and the fatality rate of the non-TGRA(0.022%)was 1.57 times that of the TGRA(0.014%).Excluding the main urban area of Chongqing,the incidence rate in other areas of the county was reduced to about half of the total incidence;in the non-reservoir counties,after eliminating the main urban area of Yichang,the incidence in other areas declined only slightly.After eliminating the impact of the main urban area,the morbidity rate in other areas of the TGRA was slightly lower than that in the non-TGRA.4.The global spatial autocorrelation showed that the incidence of bacillary dysentery in the Three Gorges Area is positively correlated at the county level,the case distribution was not random,and there was a significant spatial aggregative distribution;LISA showed that the hot-spot areas does not change much and were concentrated in the main urban areas of Chongqing,mainly Yuzhong,jiangbei,shapingba,jiulongpo,Nanan,Beibei,Yubei and Banan district.The "cold spots" area was mostly concentrated in the northeastern part of the Three Gorges Area,and is mainly Fengjie,Wushan,Xingshan,Zigui,Badong,Jianshi County and Dangyang City.5.The spatial-temporal scan statistics showed that during the period from 2005 to 2016,the occurrence of bacillary dysentery in the Three Gorges Area was time-aggregated,mainly in May-October each year.Bacillary dysentery cases had obvious clustering at the county(district)scale,and there were 12 class I clusters,35 class II clusters,and 9 clusters without statistical significance in counties with high incidence,and they were relatively stable.All the class I clusters were located in Chongqing's urban areas and its surrounding counties,and the class II clusters transformed from concentrated distribution to scattered distribution.6.In the Three Gorges Area,39 outbreaks of bacillary dysentery were reported from 2005 to 2016.Among them,19 outbreaks occurred in 11 spatial-temporal clusters.The four clustered areas were consistent with the outbreak information and the average contribution rate of the disease reached 84.90%,the four spatio-temporal aggregation areas resulted from the outbreak.The other four aggregation areas coincided with the outbreak information,and the average of the outbreak's contribution to the monthly incidence of the county was 55.54%.The outbreaks of other counties have a relatively low outbreak contribution rate,ranging from 35%to 70%.The difference is mainly due to the level of morbidity in the natural state(after eliminating the impact of outbreaks).When the incidence rate in the natural state is high,Outbreak contribution rate is low.Conclusion:The annual incidence of bacillary dysentery in the Three Gorges Area from 2005 to 2016 was significantly higher than the national average,and the decline rate was slow.The cases were mainly children under 5 years old.The main cases were scattered children.The incidence was obviously seasonal.The incidence in Chongqing's main urban area was significantly higher than that in other counties.In addition,there were some counties with high incidence or multiple outbreaks.The prevalence of disease in the TGRA and non-TGRA differs to varying degrees.After the elimination of the main urban area,the incidence in other areas of TGRA was equal to or lower than that of non-TGRA.The construction of the Three Gorges Project has no significant effect on the incidence of the disease.The incidence of bacillary dysentery in the Three Gorges Area has obvious aggregation in time and space.The Peak incidence periods were concentrated from May to October.The hot spots areas were mainly concentrated in the main urban area of Chongqing,with a little difference each year.Half of the outbreaks of bacillary dysentery occurred in the space-time aggregation area.Part of the spatio-temporal aggregation area was caused by outbreaks,and some of the spatio-temporal aggregation areas were prone to outbreaks,suggesting that passive monitoring of sporadic outbreaks and spatio-temporal scan statistics cannot replace each other.