Adoption of universal prenatal syphilis rescreening recommendations across Ontario, Canada: a difference-in-differences analysis

Introduction Congenital syphilis rates increased sharply in Ontario, Canada, between 2018 and 2023, underscoring gaps in prenatal prevention. In response, public health units (PHUs) expanded recommendations for routine repeat syphilis screening (rescreening) during pregnancy. We examined the adoption and implementation of these rescreening recommendations and assessed their impact on prenatal syphilis screening rates. Methods We conducted an environmental scan of all Ontario PHUs to identify changes to local recommendations and implementation strategies for prenatal syphilis screening between 2018 and 2023. Based on this scan, we identified nine sociodemographically comparable PHUs: four that adopted universal rescreening recommendations (intervention), and five that did not modify recommendations (control). We leveraged this variation using a difference-in-differences analysis to evaluate whether local public health recommendations were associated with changes in prenatal syphilis screening rates. Results 28 PHUs (82%) responded to the survey, representing all of Ontario’s health regions. Prenatal syphilis screening recommendations varied over time and between PHUs. By December 2023, 36% (n=10) recommended rescreening for syphilis at mid-gestation and/or at delivery. The primary drivers of adopting rescreening recommendations included changes in local (n=9; 90%), provincial (n=8; 80%) and national (n=9; 90%) syphilis epidemiology. A total of 58 103 prenatal syphilis tests (28 887 from intervention PHUs and 29 216 from control) were analysed. Accounting for multiple intervention groups and staggered adoption, universal rescreening recommendations were associated with an average of 375 more tests per 1000 pregnancies per month (95% CI 321 to 430) across intervention PHUs. The effect varied by PHU, reflecting differences in local implementation strategies and contexts. Conclusions Repeat screening recommendations were associated with an increase in prenatal syphilis screening; however, inconsistent implementation between PHUs highlights the challenges of translating public health policies into clinical practice. Co-ordinated implementation strategies are essential to ensure equitable access to timely screening for all pregnant people.