| Background Syphilis is a classic sexually transmitted disease(STD) caused by treponema pallidum subsp. pallidum, severely damaged to health of individual, which was one of the huge dangerous infectious diseases that human civilization ever faced in history. In China, syphilis has remained being an important public health issue and ranked in the third place in the legal Category A and B Communicable Diseases. It was difficult for the traditional epidemiological analysis in intuitively and accurately finding the geographical distribution of syphilis and idenfitying its influenced factors. The geographic information systems(GIS) and spatial analysis methods, being rapidly developing in recent years, could fill the gaps and provide a new solution for syphilis surveillance in China. How to establish the geographic information systems and apply it to monitor and control syphilis in China, are the key scientific problems which should be discussed and resolved in this article.Objectives The objectives includes in this study:setting up the national GIS database of syphilis in China; exploring and revealing the spatial distribution characteristics and patterns of syphilis in order to intuitively and accurately identify the hot spots over this country; generating the spatial regression model of syphilis to determine the factors influencing spatial distribution pattern of syphilis so that we could put forward the suggestions and recommendations to syphilis control in China.Methods The GIS software Maplnfo10.0was employed to set up the national GIS database of syphilis at county level in China in2011. On the basis of the GIS database, GeoDa1.46and ArcGIS software were used to conduct exploratory spatial data analysis(ESDA), including frequency analysis, global trend analysis, the global and local spatial autocorrelation methods, so as to explore the spatial distribution characteristics and pattern of syphilis. Finally, we generate the spatial regression model of syphilis in China with confirmatory spatial analysis methods to analyze the causes of syphilis spatial pattern. Results The frequency analysis showed that the median of reported incidence of syphilis was21.17/100,000population(25%percentile and75%percentile were9.28and43.00/100,000population, respectively), minimum with0.00, maximum with515.34/100,000population in all2925counties of Chinese mainland in2011, and appeared significant positive skewing(skewness was3.11). There were126counties with syphilis incidence higher than101/100,100population, which were extreme outliers. The global trend analysis indicated that the whole distribution of syphilis from northwest to southeast appeared as "U" shape and suggested that the areas of high incidence of syphilis located in northwest and southeast coastal regions in China. The global spatial autocorrelation analysis revealed a positive spatial autocorrelation(Global Moran’s I is0.5762, P<0.001) and a high-high aggregation model(General G is0.0331, P<0.001) for syphilis epidemics at county level in China. The local spatial autocorrelation analysis was further used to output the hot-spot mapping of syphilis, including primary and secondary syphilis, latent syphilis at county level, and117hot-spots counties with high incidence of primary and secondary syphilis(higher than50/100,100population) were recognized and identified, mainly distributed in southwest of Xinjiang, middle east of Qinghai, Guangxi, southeastern coast and northeast of China(including Xilin Gol League area of Inner Mongolia), etc. Further ESDA was conducted in three provinces(Fujian, Guangdong, Xinjiang) with high incidence of syphilis to identify hot-spots counties. The spatial lag regression model generated at prefecture level was statistically significant (determination coefficient R2=0.48, spatial autoregressive coefficient=0.55, P<0.0001). Per Capita GDP, number of STD medical facilities, the syphilis prevalence of floating population, FSW and MSM population are significant factors influencing the spatial distribution of syphilis(spatial regressive coefficient=3.47,0.12,4.46,1.85,0.71, respectively.P<0.05).Conclusions The hot-spots counties of syphilis were mainly distributed in southwest of Xinjiang, middle east of Qinghai, Guangxi, southeastern coast and northeast of China(including Xilin Gol League area of Inner Mongolia). Limited resources should be focused on these key areas. The strong and effective measures must be taken to strengthen the prevention and control of syphilis in these areas, especially in minority areas. The areas with more economically developed, more higher syphilis prevalence of floating population and high risk population, reported higher syphilis incidences. It likely appeared that the syphilis prevalence of floating population and FSW population had more affection on the syphilis incidence than that of MSM population and male patients in STD clinics, which is worth further research in future. GIS and spatial statistic analysis, with the advantages of visualization and accurate location, should be as important tools to apply in syphilis surveillance and control. |
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