Incidence and Epidemiological Features of Syphilis in Busan Metropolitan City, Ulsan Metropolitan City, and Gyeongsangnam-do, Republic of Korea, 2024.

Objectives: Following Republic of Korea's reintroduction of mandatory syphilis surveillance in 2024, this study aimed to characterize the reported syphilis cases in the Gyeongnam region (encompassing Busan, Ulsan, and Gyeongsangnam-do) during the initial year of this transition. Methods: We analyzed 383 syphilis cases reported to the Korea Disease Control and Prevention Agency's Integrated Disease Surveillance System from January 1 to December 31, 2024, among individuals whose registered residence was in the Gyeongnam region. Case reports and epidemiologic investigation records were summarized by sex, age group, administrative area, and disease stage. The incidence per 100,000 population was calculated using mid-year resident population data from Ministry of Data and Statistics. Results: Of the 383 reported cases, 244 (63.7%) occurred in Busan, 106 (27.7%) in Gyeongsangnam-do, and 33 (8.6%) in Ulsan. Males constituted 279 cases (72.8%). The most affected age group was 20-29 years (125 cases, 32.6%), followed by 30-39 years (96 cases, 25.1%) and 40-49 years (62 cases, 16.2%). Among respondents who answered the question on sexual contact in the past 12 months (300 cases, 79.0%), 174 (45.8%) reported having engaged in sexual contact. Conclusions: The overall patterns observed were consistent with national trends; however, the proportion of tertiary syphilis and the incidence rate were higher than the national averages. These findings may indicate the progression of previously acquired infections and delayed diagnoses rather than a recent increase in new infections. The limited response regarding risk factors constrains the interpretation of transmission routes, underscoring the necessity for enhanced investigations and the continuous accumulation of surveillance data.