Introduction There has been a rapid rise in infectious syphilis (IS) diagnoses in England since 2011 but congenital syphilis (CS) is rare. In 2016, 3 CS cases were diagnosed in geographically dispersed areas of England. Unusually, their mothers had tested negative at first trimester antenatal screen (screen-negative), indicating syphilis acquisition during pregnancy. Simulation modelling using historical CS cases indicated an event probability of 3%. We investigated the spatial and temporal relationship between screen-negative CS cases and IS epidemiology in the affected areas.
Methods Data from 01/2011-06/2016 were obtained from GUMCADv2, the national electronic surveillance system. England was divided into 3 syphilis epidemiological areas (SEAs): wider incident areas (WIAs; the 3 affected and immediate surrounding counties); endemic areas (with established epidemics in men who have sex with men-MSM) and non-incident non-endemic areas (NINEAs). Time-series analysis (TSA) was used to estimate IS outliers by gender, sexual orientation and SEA. Associations between IS characteristics and SEA (WIAs vs. NINEAs) were assessed using Pearson’s chi-square and Kruskal-Wallis tests. Mothers of CS cases were excluded from analyses.
Results In 2011–2016, IS rates/100,000 in WIAs rose in heterosexual women (1.3–3.0) and MSM (8.9–13.9) but fell in heterosexual men (3.7–3.0). In NINEAs, rates rose in heterosexual women (1.6–1.9), MSM (5.0–10.8) and heterosexual men (2.7–3.2). On TSA, IS cases significantly exceeded expected bounds in 2016 in heterosexual women in WIAs; no exceedance was seen in NINEAs. In 2016, heterosexual women with IS were more likely to be UK-born in WIAs than in NINEAs (78% vs. 39%; p<0.001). A greater proportion of MSM were bisexual in WIAs than in NINEAs (11% vs. 8%; p<0.001).
Conclusion Increased syphilis transmission in some sexual networks of MSM and a higher proportion of bisexual men in WIAs may have created more opportunities for IS acquisition in women. Efforts to raise awareness of the potential risk of acquiring syphilis during pregnancy are needed.