Global, regional, and national burden of syphilis, 1990-2021 and predictions by Bayesian age-period-cohort analysis: a systematic analysis for the global burden of disease study 2021

Objective To comprehensively assess the global burden of syphilis and related risk factors over 1990-2021, forecast future disease trends, and understand the impact of syphilis on global health. Methods Global Burden of Disease Study 2021 (GBD 2021) data were used for age-, sex-, and region-stratified analysis of the numbers and age-standardized rates (per 100,000 population) of syphilis incidence, prevalence, deaths, and disability-adjusted life years (DALYs). Next, a differential analysis of syphilis risk factors was performed. Finally, trends for years after 2021 were predicted using Bayesian age-period-cohort (BAPC) prediction models. Results In 2021, the total number of syphilis prevalence globally was 70,541,482.80 (95% uncertainty interval: 54,910,897.66-88,207,651.97), with the highest numbers noted in Central Sub-Saharan Africa [4,622.60 (95% uncertainty interval: 3,591.97-5,753.45)]. Over 1990-2021, the global age-standardized prevalence and incidence rates increased, whereas the age-standardized death and DALY rates decreased. Among all groups, infants aged <5 years demonstrated the highest age-standardized DALY rates. Moreover, the lower the sociodemographic index (SDI), the higher was the age-standardized rate. The primary factor contributing to syphilis disease burden was identified to be unsafe sex. BAPC analysis revealed an overall increase in age-standardized prevalence rate in the <5-year age group over 1990-2035, and the highest age-standardized prevalence rate occurred in the 25-34-year age group. Conclusion Between 1990 and 2021, syphilis occurrence and prevalence increased consistently. Projections indicated a continual increase in syphilis incidence in children aged <5 years, and age-standardized prevalence rates were the highest in adults aged 25-34 years. Our results regarding the epidemiological trends of syphilis and its variations across regions, age groups, and sexes may aid policymakers in addressing the global impact of the disease effectively.