Spatiotemporal trends and determinants of syphilis among heterosexual males and females in the Netherlands, 2011 to 2023

BACKGROUNDSyphilis is increasing among females and heterosexual males (heterosexuals) in Europe and other Western countries. In the Netherlands, there has been an increase in syphilis positivity and diagnoses over the last 10 years. Research on syphilis among heterosexuals and on spatiotemporal syphilis trends in the Netherlands is limited.AIMWe aimed to assess spatiotemporal trends and identify determinants of syphilis among heterosexuals in the Netherlands.METHODSThis study used national surveillance data of all sexual health centres (SHCs) and included consultations among heterosexuals tested for syphilis between 2011 and 2023. Syphilis was defined as an infectious syphilis diagnosis (primary, secondary or early latent). Spatiotemporal trends were assessed using SaTScan, adjusting for demographic and behavioural factors. We performed a multivariate logistic regression to identify demographic and behavioural determinants of syphilis.RESULTSWe analysed 694,698 STI consultations among heterosexuals and identified 686 syphilis diagnoses. We found an increase in syphilis positivity from 0.05% in 2011 to 0.23% in 2023. SaTScan identified two space-time clusters; one in the north (2020-23) and one in the south-west (2019-23) of the Netherlands. Living with HIV (adjusted odds ratio (aOR): 17.48; 95% CI: 11.75-25.08) and having symptoms (aOR: 2.73; 95% CI: 2.34-3.20) were most strongly associated with syphilis.CONCLUSIONWe found an increasing trend of syphilis among heterosexuals diagnosed at SHCs in the Netherlands. Syphilis was found in all regions. Since living with HIV was the strongest risk factor for syphilis, increased testing among heterosexuals living with HIV, both at SHCs and HIV treatment clinics, is recommended.