Clinical Characteristics and Risk Factors for Syphilis Among People Living With Human Immunodeficiency Virus: A Nationwide Population-Based Cohort Study in Korea

Background:The incidence of syphilis, a re-emerging infection linked to human immunodeficiency virus (HIV) through shared transmission routes, is increasing among people living with human immunodeficiency virus (PLH) in Korea.We aimed to evaluate the prevalence, temporal trends, and risk factors for syphilis among PLH in the Republic of Korea.Methods: Data from the National Health Insurance Service of Korea between 2002 and 2021 were analyzed to determine the incidence of syphilis in PLH.Syphilis was defined by the assigned Korean Standard Classification of Diseases code, with prescription codes for benzathine penicillin G, ceftriaxone, and doxycycline.Syphilis was classified as early or late based on the antibiotic dose.Multivariable logistic regression analysis was performed to assess risk factors for syphilis among PLH.Results: The prevalence of syphilis in PLH was 25.53% (4,193/16,422 patients).Early syphilis accounted for 85.19% (3,572/4,193) of cases, and 34.80% of PLH with syphilis experienced multiple episodes.Additionally, 23.73% of PLH with syphilis received treatment for syphilis before HIV diagnosis.In the multivariable analysis, male sex (adjusted odds ratio [aOR], 10.78; 95% confidence interval [CI], 7.87-14.78),living in the Seoul metropolitan area (comprising Seoul, Incheon, and Gyeonggi-do) (aOR, 1.24; 95% CI, 1.15-1.34),the presence of acquired immunodeficiency syndrome-related cancer (aOR, 1.36; 95% CI, 1.24-1.48),longer duration of HIV diagnosis (pre-2009 vs. 2019-2021: aOR, 1.94; 95% CI, 1.71-2.20),and the lowest economic status (aOR, 1.35; 95% CI, 1.18-1.54)were associated with higher risks of syphilis.New PLH cases and early syphilis among PLH revealed correlated trends over the study period (rho = 0.71, P < 0.01).