·The data of syphilis incidence in 31 provinces, municipalities and autonomous regions of the mainland of China in 2017 were obtained from the China Public Health Science Data Center, and the time distrbution characteristics of the incidence rates were described. The global Moran′s I index and Anselin local Moran′s I index were used to analyze the spatial cluster characteristics of the syphilis cases, and then space-time scan analysis based on Poisson distribution was used to explore the spatio-temporal distribution characteristics.

·In 2017, the number of syphilis cases in the 31 provinces, municipalities, and autonomous regions of the mainland of China was 475 860, and the incidence rate was 34.49/100 000. Latent syphilis accounted for most of the cases, reaching 76.78% (365 353/475 860). August had the highest incidence rate. For the spatial distribution, Xinjiang Uygur Autonomous Region was the provincial-level unit with the highest incidence rate of syphilis, reaching 91.80/100 000. The incidence rates of latent, secondary, tertiary, and congenital syphilis appeared with positive spatial autocorrelation (all P<0.05). The high-high clusters of secondary and tertiary syphilis appeared in Shanghai, Jiangsu, and Zhejiang (all P<0.05), respectively, while the high-high clusters of congenital syphilis appeared in Xinjiang and Tibet (P=0.000). The results of space-time scan analysis showed that the main cluster appeared from April to September in Fujian, Jiangxi, Zhejiang, Shanghai, Jiangsu, Hunan, Anhui, and Guangdong (P=0.000). Compared with the outside area, the relative risk of syphilis in this cluster was 1.59 times.

·The incidence rate of syphilis in China is relatively high. There are differences in the types and periods of syphilis prevention and control among provinces, municipalities and autonomous regions. From April to September, Fujian, Jiangxi, Zhejiang, Shanghai, Jiangsu, Hunan, Anhui and Guangdong are the key areas for syphilis prevention and control in the mainland of China.