Abstract: 【Abstract】 Objective To investigate the epidemiological trends and spatio-temporal distribution characteristics of syphilis in China from 2010 to 2023. Methods Data on syphilis cases reported from 31 provinces, autonomous regions or municipalities from 2010 to 2023 were collected from the Infectious Diseases Surveillance System of Chinese Disease Prevention and Control Information System. Joinpoint 5.2.0 software was used to analyze the epidemiological trends of syphilis, ArcGIS 10.5 software was used for spatial autocorrelation analysis at the county level, and SaTScan 10.2.3 software was used for space-time scan analysis. Results The national reported incidence rates of syphilis increased from 26.86 per 100 000 in 2010 to 37.60 per 100 000 in 2023, with an average annual percent change of 1.82% （95% CI: 0.81% - 2.89%）, and the upward trend in the reported incidence rates was statistically significant （P = 0.002）. There was a positive spatial autocorrelation in the reported incidence rates of syphilis at the county level in China （Moran's Ⅰ range: 0.47 - 0.60, all P < 0.001）, and all of the Getis-Ord general test statistic Z（G）values were > 1.96, indicating a high-value clustering pattern in the reported incidence rates of syphilis. The local spatial autocorrelation analysis showed that the annual number of hotspot areas ranged from 180 to 294, which were mainly located in Xinjiang, Qinghai, Guizhou, Sichuan and Yunnan. A total of 92 spatio-temporal clusters were identified by space-time scan analysis, which were mainly distributed in Zhejiang, Guangxi, Guangdong and Fujian from 2010 to 2012, in Xinjiang from 2013 to 2017, and in Sichuan, Guizhou, Chongqing, etc., from 2019 to 2023. Conclusions From 2010 to 2023, the reported incidence rates of syphilis in China exhibited a fluctuating increase on the whole, with obvious spatio-temporal clustering characteristics. The hotspot areas were basically consistent with the spatio-temporal clusters, and were mainly distributed in the northwestern, southeastern coastal and southwestern areas. Over time, the spatio-temporal clusters gradually changed from the southeast coastal and northwestern areas to the southwestern areas.

Key words: Syphilis, Incidence rate, Epidemiological trend, Spatio-temporal analysis