In the study, exploratory spatial data analysis and spatial cluster analysis of HFRS were conducted at county level of mainland China. We mapped HFRS from different aspects such as crude incidence, excess risk, spatial smoothed incidence, and incidence with IDW, evaluated the spatial pattern and highlighted geographic areas with significant high incidence of HFRS in mainland China. Furthermore, this study demonstrated that additional tools necessary for disease surveillance could be provided for public health officials using existing health data, GIS and spatial scan statistics.
The study showed that the spatial distribution of HFRS in mainland China was nonrandom and clustered with a Moran's I of 0.5044 (p = 0.001) from 1994 through 1998. Spatial cluster analysis identified 16.51% total population and 26 areas increased HFRS risk when a maximum spatial cluster size of ≤ 20% total population was used. Additional cluster analysis based on a maximum spatial cluster size of ≤ 10% total population identified 39 subclusters occupied by 18.42% of the total population, which had statistically significant (p < 0.01) increased HFRS risk. The results suggest that there were "hot-spots" of HFRS in a number of areas in China, which were also the priority areas of public health planning and resource allocation for preventing HFRS. For instance, there were large areas (> 10,000 km2) of increased HFRS risk existed in Shandong, Hebei, Heilongjiang, Hunan, Zhejiang, Jiangxi, and Guangxi provinces, and some small areas (≤ 10,000 km2) with increased HFRS risk in some other provinces of central, eastern and north-eastern China.
The spatial distribution of HFRS was correlated with density, species and infection rate of rodents as the major animal reservoirs, which were influenced possibly by natural and social-economic environmental conditions such as the elevation, land use, soil type, vegetation, precipitation, atmospheric temperature, et al [21, 22]. To identify and measure quantitatively the most important determinants of HFRS distribution, and to assess the burden of illness due to HFRS, more detailed epidemiological investigations need to be carried out. Clusters with significantly high incidence of HFRS identified will be helpful of investigating the underlying causes of increased risk in the identified areas, landscape attributes and identification of the environmental variables characteristic of high-risk areas with different acreage. Environmental and landscape characteristics, socio-economic factors associated with increased risk for HFRS infections need to be studied.