Elimination of congenital syphilis: a nationwide register-based study, Denmark, 2010 to 2024

BACKGROUNDCongenital syphilis is a potentially serious, but preventable infection. Several European countries have recently reported increasing trends.AIMThis study assessed national incidence and temporal trends of congenital syphilis and prevalence of pregnancies with active syphilis in Denmark between 2010 and 2024.METHODSUsing nationwide individual-level data linked through civil registration numbers across Danish health and population registers, we identified all maternal and congenital syphilis cases among live-born children born in Denmark from 2010 to 2024. We calculated annual incidence per 10,000 live births and analysed temporal trends and annual percent change (APC) with 95% confidence intervals (CI), using Poisson or negative binomial regression models.RESULTSFive infants with confirmed congenital syphilis were recorded among 894,345 live births, corresponding to an incidence of 0.6 per 100,000 (95% CI: 0.2-1.4). No infants with congenital syphilis were identified after 2016. For each infant, a plausible explanation for screening failure was identified: two women arrived in Denmark late in pregnancy, two were infected late in pregnancy. None of these events reflected failure of the first-trimester screening algorithm itself. One event was due to a reporting irregularity. Poisson regression showed a decreasing trend (APC = -21.7%; 95% CI: -43.4 to -1.0). Active syphilis infection occurred in 172 pregnancies, amounting to 20.0 per 100,000 live births (95% CI: 17.2-23.2) with no temporal changes.CONCLUSIONSCongenital syphilis is now eliminated in Denmark. The incidence of pregnancies with active syphilis infection remained stable despite increasing syphilis prevalence in the general population, confirming the continued effectiveness of the Danish national antenatal syphilis screening programme.