Study On Spatiotemporal Distribution And Environmental Risk Factors Of Hemorraghic Fever With Renal Syndrome

Background: Hemorrhagic fever with renal syndrome (HFRS), a rodent-borne disease caused by Hantaviruses (HV), is characterized by fever, acute renal dysfunction and hemorrhage manifestations. It is one of the key infectious diseases harming people's health and safety with wide distribution, high incidence and complicated type of endemic areas in mainland China. At present, HFRS is endemic in all 31 provinces, autonomous regions, and metropolitan areas in mainland Chian and accounts for 90% of the HFRS cases reported globally. Although the overall incidence of HFRS in China decreased obviously since 2000, the scope of HFRS endemic area is still expanding, and the areas of hotspot with high incidence are changing with significantly increasing incidence in some areas, such as some local places in northeast China and north China, being ranked as one of the most serious infectious diseases. Noticeably, seasonal pattern of HFRS cases is linked with the serotype of HVs, animal hosts. Also, the measures of prevention and control measures to be taken are different. Since 1980s, changes of seasonal pattern of HFRS cases had occurred popularly in mainland China, but the detail on transformation dynamics and its environmental factors in different regions is not clear. Therefore, it is necessary to study the spatial temporal dynamics and the rule of endemic area's transformation at different spatial scales and type of endemic area by choosing the national level, a newly-established endemic region and a traditional high-incidence area, as well as to study the association between HFRS incidence for different types of endemic areas and the environmental factors. These will be helpful for understanding the spatiotemporal pattern of HFRS cases, providing clue to changes of endemic areas'types, identifying the targets of measures, and promoting prevention and control of HFRS.Objective: To study the temporal and spatial pattern of HFRS cases, endemic areas'type and its changes, the characteristics of HFRS endemic areas'outspread, as well as their environmental determinants at different temporal and spatial scales in mainland Chian and to farther establish the decision-making system for prevention and control of HFRS, in order to facilitate a more comprehensive understanding of spatiotemporal dynamics and their determinants of HFRS cases and provide a scientific basis for the targeted measures of prevention and control of HFRS in mainland China.Methods: The surveillance data of HFRS epidemic from 1994 to 2008 in the whole country, 1997 to 2006 in Beijing, and 1968 to 2005 in Shandong Province were collected and processed. Based on the data, a GIS database of HFRS epidemic was established by linking these data to digital maps at different spatiotemporal scales. Spatiotemporal dynamics and their environmental determinants of HFRS cases for different type of endemic areas were studied by comprehensive application of cluster analysis of time-space scanning, spatial trend surface analysis, Poisson regression model with principal component, and so on. Here we chose and used land use data as environmental factors for these studies due to its direct or indirect relationship with changes of natural environment and socio-economic environment. Softwares such as ArcGIS9.2, ENVI4.2, SaTScan8.0, Geoda 0.9i, Origin7.5, and STATA10.0 were used in this study.Results:1. Since 2000, the overall incidence of HFRS decreases in mainland China, but the scope of HFRS endemic areas enlarge obviously with lots of newly-established endemic areas, and the incidence still increases in about 1/3 of all endemic areas. Since 2000, the HFRS endemic areas with increased incidence are distributed mainly surrounding the original endemic areas and located in the northeast, north, west and southern regions of the original endemic areas, while the endemic areas with declining incidence are relatively concentrated on the eastern and central region of China. In addition, the newly-established endemic areas of HFRS are mainly located in the western, northern and southern regions of original endemic areas, while the reduced endemic areas are mainly distributed in southwestern China and there are less endemic areas reduced in north China. 2. The predictive map of HFRS seasonal distribution shows the seasonal pattern of HFRS cases in mainland China as follows: from the northeast to southwest, the different type of endemic areas arrange according to this rank, the endemic areas of autumn/winter-type→endemic areas of bimodal type→endemic areas of spring-type→endemic areas of bimodal type→endemic areas of autumn/winter-type→endemic areas of bimodal type→endemic areas of spring-type. The borders between two types of endemic areas are vague in the most endemic areas except for the north, north-west China.3. We find that the incidence in HFRS endemic areas of autumn/winter-type, spring-type, and bimodal type are all closely related to land use. It is not always the same on the influence to HFRS epidemic in different endemic areas resulted from some variables from land use. For instance, built-up land has the influence of protection to the endemic areas of autumn/winter-type, while it can add the epidemic risk for endemic areas of spring-type. Compared to endemic areas of endemic areas of autumn/winter-type, and spring-type, it has the in-between influence for the endemic areas of bimodal type. This result indicate that the change of land use may lead to the the change of type of HFRS endemic area. For instance, urbanization increases the area of built-up land, which results in the added risk of HFRS epidemic of spring-type and decease the risk of HFRS epidemic of autumn/winter-type, subsequently. The result can provide clue to the cause on the changing of endemic areas'type occurred popularly in the 1980s.4. land-use types'influence on HFRS epidemic has this pattern of multi-collinearity and it usually come from the habitat reflected by the combination of different types of land use.5. The velocity vector map to visualize spread of HFRS over time indicate that the rapid propagation of HFRS endemic areas from its epicenter in Rizhao, Linyi, Weifang regions in southern Shandong province and its spread north, north-east and south-west into new counties and foci. by using space trend surface model. 6. We demonstrated the spatial and temporal dynamic of scope of endemic areas and their changing patterns, seasonal pattern of HFRS cases and their changing patterns, as well as the spatiotemporal dynamics of HFRS cases and their changing patterns in Shandong Province. Three periods associated with HFRS incidence, seasonal pattern of HFRS cases and their changing patterns were identified and indicated that the second period (the period from 1983 to 1985) was the phase of the change of type of HFRS endemic area in Shandong Province.7. We established the GIS decision-making system of HFRS.Conclusion: Based on the establishment of HFRS GIS database by collecting the data of HFRS epidemic in the country, Beijing and Shandong Province in this study, the spatial temporal distribution and environmental risk factors of HFRS for endemic areas of different types were studied by using synthetically space-time scanning cluster analysis, spatial trend surface model, Poisson regression combined with principal component analysis methods. This study detected the space-time hot spots of HFRS epidemics, and demonstrated the spatial and temporal dynamic of scope of endemic areas and their changing patterns, seasonal patterns of HFRS cases and their changing patterns, as well as the spatiotemporal dynamics of HFRS cases and their changing patterns. This study also identified the association between HFRS incidence of three-type endemic areas and land use. In addition, the GIS decision-making system of HFRS was established in the study. The results above not only provides the basis of data for the the risk assessment of HFRS epidemic resulted from economic and tour development, also can provide the clue for researching the cause on the changing of endemic areas'type and provide scientic basis for targeting the suitable measures of prevention and control according to different type of endemic areas in mainland China.