Introduction In past twenty years, incidence of syphilis has been increasing and remained a public issue in China. In order to precisely control syphilis epidemic in the country, it was very important to explore and understand the spatial distribution pattern of syphilis in county level in China.

Methods We used the software of ArcGIS(version 10) to set up the national geographic information system(GIS) database of syphilis of all counties in China in 2015. The exploratory spatial data analysis(ESDA), including frequency, the global and local spatial autocorrelation methods were used to explore the spatial distribution characteristics of syphilis.

Results The median of incidence of syphilis was 26.05/100,000 population (25% percentile and 75% percentile were 15.70 and 44.77/100,000 population, respectively), minimum with 0.84, maximum with 433.28/100,000 population in all 2925 counties of Chinese mainland in 2015, and appeared significant positive skewing (skewness was 3.19). 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 showed a positive spatial autocorrelation (Global Moran’s I is 0.5962, p<0.001) and a high-high aggregation model (General G is 0.0441, p<0.001) for syphilis epidemics in 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 in county-level, and 117 hot-spots counties with high incidence of primary and secondary syphilis were recognised and identified, mainly distributed in Yangtze River delta, north-west, north-eastern and south China.

Conclusion GIS and exploratory spatial data analysis, with the advantages of visualisation and accurate location, should be as an important tool to apply in syphilis surveillance and control.