Introduction: Mongolia's health ministry prioritizes control of Sexually Transmitted Infections, including syphilis screening and treatment in antenatal care (ANC).
Methods: Adult syphilis prevalence trends were fitted using the Spectrum-STI estimation tool, using data from ANC surveys and routine screening over 1997-2016. Estimates were combined with programmatic data to estimate numbers of treated and untreated pregnant women with syphilis and associated incidence congenital syphilis (CS) and CS-attributable adverse birth outcomes (ABO), which we compared with CS case reports.
Results: Syphilis prevalence in pregnant women was estimated at 1.7% in 2000 and 3.0% in 2016. We estimated 652 CS cases, of which 410 ABO, in 2016. Far larger, annually increasing numbers of CS cases and ABO were estimated to have been prevented: 1654 cases, of which 789 ABO in 2016 - thanks to increasing coverages of ANC (99% in 2016), ANC-based screening (97% in 2016) and treatment of women diagnosed (81% in 2016). The 42 CS cases reported nationally over 2016 (liveborn infants only) represented 27% of liveborn infants with clinical CS, but only 7% of estimated CS cases among women found syphilis-infected in ANC, and 6% of all estimated CS cases including those born to women with undiagnosed syphilis.
Discussion/conclusion: Mongolia's ANC-based syphilis screening program is reducing CS, but maternal prevalence remains high. To eliminate CS (target: <50 cases per 100,000 live births), Mongolia should strengthen ANC services, limiting losses during referral for treatment, and under-diagnosis of CS including still-births and neonatal deaths, and expand syphilis screening and prevention programs.
Keywords: ABO, Adverse Birth Outcome; ANC, antenatal care; ANC-1, attendance of antenatal care at least once during a pregnancy; Antenatal care; CI, confidence interval; CS, Congenital Syphilis; Congenital syphilis; Epidemiological modelling; F, women; N, sample size tested; NCCD, Mongolia National Center for Communicable Diseases; RPR, Rapid Plasma Reagin test; STI, sexually transmitted infection; Screening; Surveillance; Syphilis; TP, Treponema pallidum; WHO, World Health Organization.