Epidemiological Features and Temporal Trends of Five Common Sexually Transmitted Infections Excluding HIV, 1990–2021: Findings From the Global Burden of Disease Study

Sexually transmitted infections (STIs) remain a major global health threat. A comprehensive assessment of their epidemiological features and future trajectories is essential for informing targeted public health policies and achieving international control targets. Using data from the Global Burden of Disease (GBD) Study 2021, we evaluated the incidence of five common STIs (trichomoniasis, chlamydial infection, gonococcal infection, genital herpes, and syphilis). We applied hierarchical clustering to evaluate regional temporal trends, decomposition analysis to identify drivers of burden variations, and frontier analysis to assess burden reduction potential relative to development levels. A Bayesian age-period-cohort model with integrated nested Laplace approximation was employed to project future age-standardized incidence rates (ASIR) through 2035. In 2021, ~723 million new STIs cases were reported globally. Trichomoniasis accounted for the highest proportion of cases (46.60%), followed by chlamydial (32.70%) and gonococcal infections (12.40%). From 1990 to 2021, the global ASIR remained statistically stable (EAPC -0.02, 95% CI -0.07 to 0.03). Unsafe sex was the leading risk factor, accounting for 16.25% of global STIs-related DALYs in 2021, with the highest attribution observed in high Socio-Demographic Index (SDI) regions. Population growth drove 84.84% of the absolute burden increase. Notably, high STIs burdens persisted in regions like South Africa despite its relatively high SDI. While overall ASIR is projected to decline through 2035, a significant demographic shift is expected: the steepest decline is projected in the 20-24 age group, while increasing trends are predicted for the 40-44 age group and children aged < 5 and 10-14 years. Despite stable global incidence, the shifting age profile and persistent regional disparities indicate that "one-size-fits-all" strategies are insufficient. Public health interventions must be recalibrated to address the rising burden in middle-aged populations and the specific needs of high-burden regions to meet the WHO 2030 targets.