Background The World Health Organization (WHO) periodically estimates global and regional prevalence and incidence of four curable sexually transmitted infections (STIs): chlamydia, gonorrhoea, trichomoniasis and syphilis.

Methods For chlamydia, gonorrhoea, and trichomoniasis, WHO estimates for 2012 were based upon literature reviews of prevalence data from 2005 through 2012 among general populations. For syphilis, nationally reported data on syphilis seroprevalence among antenatal care attendees were used. Data were adjusted for laboratory test type, geography, age, and high risk subpopulations, and combined using a Bayesian meta-analytic approach. Regional incidence estimates were generated from prevalence estimates by adjusting for average duration of infection.

Results In 2012 the estimated global prevalence among women aged 15–49 years of chlamydia was 4.2% (95% uncertainty interval (UI): 3.7–4.7%), gonorrhoea 0.8% (0.6–1.0%), trichomoniasis 5.0% (4.0–6.4%), and syphilis 0.5% (0.4–0.6%); among men, estimated chlamydia prevalence was 2.7% (2.0–3.6%), gonorrhoea 0.6% (0.4–0.9%), trichomoniasis 0.6% (0.4–0.8%), and syphilis 0.48% (0.3–0.7%). These figures correspond to an estimated 131 million new cases of chlamydia (100–166 million), 78 million of gonorrhoea (53–110 million), 143 million of trichomoniasis (98–202 million), and 6 million of syphilis (4–8 million) in 2012. Prevalence and incidence estimates varied by region and sex.

Conclusions Estimated global prevalence and incidence of chlamydia, gonorrhoea, trichomoniasis, and syphilis in adult women and men remain high, with nearly one million new infections each day. These estimates highlight the urgent need for well-recognized effective interventions for STI prevention, screening, diagnosis, and treatment to be made more widely available. Improved estimation methods are needed to allow use of more varied data and to generate national-level estimates.