The burden of sexually transmitted infections excluding HIV in China: trends from 1990 to 2021 and exploratory Bayesian projections to 2035

Background Sexually transmitted infections (STIs) excluding HIV remain a substantial public health concern worldwide. This study aimed to assess the burden and long-term epidemiological trends of STIs excluding HIV in China from 1990 to 2021 and project their burden through 2035. Methods Using Global Burden of Disease (GBD) 2021 data, we analyzed prevalence, incidence, deaths, and disability-adjusted life years (DALYs) attributable to STIs excluding HIV in China, with sex-specific and geographic comparisons. Age-period-cohort (APC) analysis was performed to evaluate age, period, and cohort effects. Decomposition analysis was used to quantify the contributions of population aging, population growth, and epidemiological changes to disease burden. A Bayesian age-period-cohort (BAPC) model was applied to project the disease burden through 2035. Results From 1990 to 2021, prevalent cases of STIs excluding HIV in China increased from 152.25 million to 235.36 million, while incident cases rose from 123.88 million to 148.27 million. In contrast, deaths decreased from 4,893 to 2,235, and DALYs declined from 559,483 to 377,058. Age-standardized prevalence and incidence rates remained relatively stable, whereas age-standardized mortality and DALY rates declined. Genital herpes accounted for the largest number of prevalent cases, while the leading cause of incident cases shifted from chlamydial infection in 1990 to trichomoniasis in 2021. Syphilis contributed the greatest mortality and DALY burden. Prevalent and incident cases were concentrated among adults, whereas deaths and DALYs were predominantly observed in children younger than 5 years. Decomposition analysis identified population growth as the main contributor to increases in prevalent and incident cases in China. The BAPC model projected 247.54 million prevalent cases, 125.41 million incident cases, and 224648 DALYs in 2035. Corresponding age-standardized rates were projected to be 13,574.66, 9,105.25, and 20.48 per 100,000 population, respectively. Mortality projections showed substantial uncertainty and limited predictive reliability in temporal validation. Conclusion From 1990 to 2021, China experienced an increasing burden of STIs excluding HIV in terms of prevalent and incident cases, despite declining mortality and DALYs. Exploratory projections suggest a substantial burden through 2035, although mortality forecasts remain uncertain. These findings underscore the need for targeted STI prevention and control, particularly for high-burden infections and priority populations.