Characterization of spatial distribution of syphilis in China, 2011

Abstract

Objective To characterize the spatial distribution pattern of syphilis at the county level in China,and to provide a new method for syphilis surveillance and control.Methods A national geographic information system (GIS) database was developed based on reported cases of syphilis from all counties in China,2011.Exploratory spatial data analysis (ESDA) methods were used to study the frequency distribution of incidence,global and local spatial autocorrelation,of syphilis.Results The median incidence rate of syphilis was 21.17/100 000 (range:0.00-515.34/100 000; 25th percentile 9.28/100 000,75th percentile 43.00/100 000) in 2 925 counties in the mainland of China in 2011,with a highly positively skewed distribution (skewness =3.11).The global spatial autocorrelation analysis showed a positive spatial autocorrelation of syphilis incidence at the county level in China (global Moran's index =0.576 2,P ＜ 0.001),with the type of correlation being high-high cluster (General G index =0.033 1,P ＜ 0.001).The local spatial autocorrelation analysis delineated hot spots of syphilis (including primary and secondary syphilis,latent syphilis) at the county level.Totally,117 counties,which were mainly distributed in the Yangtze River delta region,northwest,northeastern and south China,were identified as hot spots for syphilis,with the incidence rate of primary or secondary syphilis being higher than 50/100 000.Conclusions The GIS and exploratory spatial data analysis,with the advantages of visualization and accurate localization,may serve as an important novel tool for syphilis surveillance and control. Key words: Syphilis; Geographic information systems; Spatial analysis