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[Spatial Effect of the Dams and Sluices on the Risk of Schistosomiasis in Dongting Lake Region of Hunan Province].

OBJECTIVE
To determine the spatial effect of the dams and the sluices on the risk of schistosomiasis in Dongting Lake Region, and its mechanism, type and degree.


METHODS
The positions, levels and types of the dams and the sluices in Dongting Lake Region of Hunan Province were marked on the base map. Epidemiological data of schistosomiasis among populations in 334 Townships in the Region were collected during March and July in each year of 2010-2014, and the 5-year average infection rate was calculated. A grid system composed of 1 220 hexagons was built to spatially quantify the effect of the dams and the sluices on the risk of schistosomiasis and the infection rates among populations. A two-step clustering was used to analyze the grid system, and the areas of infection peak were identified. The centrifugal model was used to simulate the degree and scope of the influence of these infection peak areas on the surrounding regions. The correlation coefficient model was used to determine the correlation coefficients between the dams and sluices and the spatial distribution of schistosomiasis. The correlation coefficients were then weighted, the integrated weighted risk of all grid cells calculated, and the weighted distribution figure for schistosomiasis risk produced.


RESULTS
The results of two-step clustering revealed 15 areas of infection peak in the Region. The results of centrifugal model showed that the areas of infection peak significantly promoted the effect of the surrounding regions on the risk of infection. The correlation coefficients of the dams and the sluices with the infection rate among populations were 0.82 and 0.86, with the weights being 0.488 1 and 0.511 9, respectively. The areas with high and relatively high risks of infection had a Crescent-shaped distribution along the Lishui River, West Dongting Lake, South Dongting Lake, East Dongting Lake and Chenglingji. The results were further verified by MAE testing.


CONCLUSION
The dams and sluices correlated strongly and positively with the risk of schistosomiasis. Fifteen areas of infection peak are identified to be determinant for schistosomiasis infection and spread, and have significant gradient spatial effect on schistosomiasis risk in surrounding areas.