Re-emerging syphilis among women of reproductive age: temporal dynamics, demographic drivers, inequalities and projections to 2046.

BACKGROUND

Syphilis is a re-emerging sexually transmitted infection and a major threat to reproductive and maternal health. Previous studies have described the burden among women of reproductive age (WRA), but have not quantified the demographic drivers of rising case numbers or compared changes in absolute and relative socioeconomic inequality. We examined these questions from 1990 to 2021 and projected trends to 2046.

METHODS

We analyzed Global Burden of Disease Study 2021 estimates of syphilis incidence and prevalence among women aged 15-49 years in 204 countries and territories. Temporal patterns were assessed using Joinpoint regression and age-period-cohort analysis. Decomposition analysis quantified demographic and epidemiological drivers. Socio-demographic Index (SDI)-related inequalities were measured using the slope index of inequality and relative concentration index, and future burden was projected using Nordpred models.

RESULTS

In 2021, the global age-standardized incidence and prevalence rates were 279.2 and 1057.3 per 100,000 women, corresponding to 5.36 million incident and 20.5 million prevalent cases. Burden remained concentrated in lower-SDI regions and among women aged 20-29 years. Population growth accounted for 97.97% of the increase in incident cases and 99.90% of the increase in prevalent cases, while population aging partly offset both increases. Absolute socioeconomic gaps narrowed, whereas relative inequality changed little. Period rate ratios increased again during 2017-2021, and annual incident cases were projected to reach 6.95 million by 2046.

CONCLUSIONS

Stable age-standardized rates did not translate into fewer women affected. Demographic growth and persistent relative inequality should be considered in surveillance and service planning, particularly in lower-SDI settings.