Abstract
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.
Keywords: Public Health, Sexually Transmitted Diseases, Epidemiology, Public Health Practice
WHAT IS ALREADY KNOWN ON THIS TOPIC
Congenital syphilis is a reemerging public health crisis worldwide; routine rescreening for syphilis during pregnancy has been adopted in some jurisdictions with varying success.
Despite a steep rise in congenital syphilis rates across Canada between 2018 and 2023, no provincial policies have been implemented in Ontario, Canada, to increase prenatal syphilis screening.
WHAT THIS STUDY ADDS
Despite limited guidance from provincial authorities, several local Ontario public health units recommended increasing the number of routine prenatal syphilis screens.
Shifting syphilis epidemiological trends were identified as a significant driver for adopting rescreening recommendations.
Challenges and structural barriers, including healthcare provider knowledge gaps, limited capacity for client follow-up and lack of resources to conduct testing, were encountered during implementation.
Using a quasi-experimental design that controlled for secular trends and staggered adoption, we found that changes to recommendations, on average, significantly increased monthly prenatal syphilis screening rates; however, the magnitude of this increase varied by local implementation practices and contexts.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
Our findings demonstrate local adoption of universal prenatal syphilis rescreening as a public health strategy in the absence of provincial-level recommendations.
Our research highlights the importance of investing in implementation infrastructure and leadership to promote screening uptake and to maximise the population-level benefits of routine rescreening for syphilis during pregnancy.
Introduction
Congenital syphilis is caused by vertical transmission of Treponema pallidum during pregnancy or delivery and can result in severe adverse outcomes, including stillbirth and neonatal death.1 2 Fortunately, timely diagnosis and treatment during pregnancy can cure maternal infection and virtually eliminate the risk of vertical transmission.2
In 2022, the World Health Organization (WHO) estimated 700 000 congenital syphilis infections globally, which were associated with 390 000 adverse birth outcomes, including approximately 150 000 early fetal deaths and stillbirths.3 Historically, low-income and middle-income countries and low-resource settings have been disproportionately affected by a high burden of infectious syphilis and congenital syphilis.4 5 However, more recently, high-income countries in the Americas, Europe and Western Pacific have experienced a rapid resurgence in infectious syphilis and concerning rises in congenital syphilis infections.4 5
In 2016, member states of the Pan American Health Organization (PAHO), including Canada, reaffirmed their commitment to eliminating congenital syphilis as a public health problem by 2030.6 7 Since then, 11 countries in the Americas have become certified for the elimination of mother-to-child transmission of syphilis.7 Despite this progress, the incidence of syphilis in the Americas has surged, rising by 30% between 2020 and 2022, with a nearly twofold increase in syphilis rates among pregnant women between 2016 and 2022.6 In 2022, the estimated congenital syphilis rate in the Americas was 4.98 cases per 1000 live births, nearly ten times the PAHO 2030 elimination target of 0.5 cases per 1000 live births.6 Canada is among PAHO member states currently facing alarming increases in congenital syphilis, with a 5200% rise (from 1 to 53 reported cases) between 2014 and 2023.8
The WHO recommends that all pregnant women be screened for syphilis at least once, ideally at their first prenatal visit.6 Additional screening during pregnancy is typically advised for individuals at high risk of infection or those living in areas with syphilis outbreaks.9 10 However, risk-based screening approaches can be insufficient when risk factors are subtle, stigmatised or undisclosed, and adherence to risk-based screening recommendations has been found to be suboptimal.9 11 Insufficient screening frequency has been identified as a primary missed opportunity for congenital syphilis prevention.12 13 In 2024, the American College of Obstetricians and Gynecologists updated its recommendations to suggest abandoning a risk-based approach in favour of universal syphilis rescreening in the third trimester and at delivery.14 Currently, 18 of 50 states in the USA have a legal requirement for universal syphilis rescreening in the third trimester and/or at delivery.15 16 As of 2023, guidelines in seven of Canada’s thirteen provinces and territories include universal rescreening for syphilis at mid-gestation and/or at delivery.17 Despite the presence of legal or policy-based mandates, limited research has shown variable adherence to universal rescreening across jurisdictions.916 18,21
Ontario, Canada’s most populous province, experienced a 1188% rise in congenital syphilis rates between 2018 and 2023.8 17 Yet, no provincial policy has been introduced to recommend universal rescreening in pregnancy. Anecdotal reports from local public health units (PHUs) suggested that some jurisdictions may have independently adopted universal rescreening protocols. To better understand Ontario’s public health response to the rising syphilis burden, we examined syphilis screening practices across local PHUs and identified drivers of local public health decision-making that led to the adoption of universal rescreening strategies. Then we leveraged the heterogeneity in recommendations between local PHUs to examine whether adoption of universal rescreening was associated with increases in prenatal syphilis screening rates.
Materials and methods
Our research process was grounded in an integrated knowledge translation (iKT) approach, which involved collaborating with public health knowledge users at each stage. First, an environmental scan was designed to identify Ontario PHUs that had implemented universal prenatal syphilis rescreening recommendations and to contextualise local policy and practice. Second, we used a quasi-experimental design to evaluate the real-world adoption of universal prenatal syphilis rescreening recommendations. A schematic of the overall study methodology is presented in the online supplemental figure S1.
Setting: the Ontario public health system
Canada has a universal, publicly funded healthcare system administered by its ten provinces and three territories.22 Ontario, the country’s most populous province, had an estimated population of 15.8 million at the end of 2023.23 The province’s public health system is decentralised, comprising 34 local PHUs as of December 2023, each responsible for planning and delivering public health programmes and services within its municipal or regional jurisdiction.24 These responsibilities are carried out in accordance with the Health Protection and Promotion Act, R.S.O. 1990, c. H.7, and the Ontario Public Health Standards.24 25 The Ontario Ministry of Health provides strategic direction and oversight through the development of policies and legislation, administration of accountability agreements and monitoring of compliance with the Ontario Public Health Standards.24 25 Each PHU, in collaboration with partners, is then responsible for infectious disease prevention and control, including developing local prevention recommendations and interventions, as well as managing outbreaks of diseases of public health significance, including infectious and congenital syphilis.24 25
Stage I: describe prenatal syphilis screening practices across Ontario’s PHUs
We developed a web-based survey using Qualtrics to collect respondent demographics and PHU-level information related to prenatal syphilis screening practices, changes to prenatal syphilis screening recommendations, implementation practices, barriers to implementation and prenatal syphilis screening promotion strategies across Ontario’s PHUs between 2018 and 2023. The survey consisted of 15 items, including multiple-choice, short-answer and open-ended questions (survey questionnaire available in online supplemental appendix 1). Two researchers on the study team developed the survey, and it was then iterated based on feedback from a multidisciplinary team, including a senior public health decision-maker, an epidemiologist, a sexual health programme manager and a registered public health nurse. The survey was then piloted by knowledge users to ensure clarity and flow. We disseminated the survey through an established internal organisational network of PHU infectious disease and/or sexual health department managers across all 34 PHUs between September 2024 and April 2025. The target response rate was one response per PHU.
To contextualise survey findings, we synthesised publicly available data sources, including provincial infectious disease reports, provincial public health surveillance reports, and local medical advisories. These sources were used to extract annual provincial and PHU-specific infectious syphilis rates in females aged 15 to 49 years per 100 000 population and congenital syphilis rates per 100 000 live births. Details on data sources and rate calculations are available in online supplemental appendix 2. Demographic and structural information for each PHU, including Ontario health region designation, urban or rural classification and governance model, was obtained from publicly available provincial and national datasets.24 26 27
Analysis
Syphilis epidemiology and PHU demographic data were summarised at both the provincial and PHU levels. Quantitative survey responses were aggregated at the PHU level by combining data from respondents affiliated with the same PHU. Characteristics were compared between PHUs using Cohen’s d (continuous variables) and Fisher’s exact tests (categorical variables). Qualitative data from open-ended survey responses and comments were extracted into Microsoft Excel and analysed using inductive thematic analysis. Two researchers independently and iteratively coded the data to identify key subthemes.28 Emerging subthemes were reviewed collaboratively and organised into overarching thematic categories to capture common patterns across PHUs.
Stage II: examine the adoption of universal prenatal syphilis rescreening recommendations
Data source
Data on prenatal syphilis screening, maternal demographics and neighbourhood-level indicators of social determinants of health were obtained from the provincial public health laboratory (Public Health Ontario Laboratory (PHOL)) for 1 January 2019 to 31 December 2023. Laboratory serological testing of whole blood samples is the standard for routine syphilis screening in Canada.10 In Ontario, the PHOL employs a three-stage reverse algorithm for serological testing, consisting of (1) an initial qualitative chemiluminescent microparticle immunoassay (CMIA) screen for syphilis-specific antibodies, followed by (2) a semi-quantitative non-treponemal rapid plasma reagin test for reactive specimens, and (3) a confirmatory qualitative Treponema pallidum particle agglutination assay.29 We extracted records for prenatal specimens submitted to PHOL for CMIA screening for females aged 15 to 49 years. Records were excluded if individuals resided in more than one Ontario PHU during the study period. We approximated the number of monthly pregnancies in each PHU based on the annual number of live births, stillbirths and therapeutic and surgical abortions occurring per PHU, sourced from publicly available reproductive health data from Public Health Ontario (detailed in online supplemental appendix 2). Maternal age, grouped in 5-year intervals, was obtained from laboratory requisition forms. Two dimensions of neighbourhood-level marginalisation quintiles (material resources and racialised and newcomer populations) from the Ontario Marginalization Index (ON-Marg) were estimated using 2021 Canadian Census data and assigned based on residential postal codes; technical details on ON-Marg have been published elsewhere.30
Study population
Nine PHUs that participated in the survey agreed to release prenatal syphilis screening data from the PHOL. These nine PHUs are classified as peer group E (n=2) and I (n=7) health regions based on the Statistics Canada 2023 Peer Group Classification. The Peer Group Classification was developed to facilitate comparisons of health-related outcomes between and within Canadian health regions that share similar population-level socio-economic characteristics, including demographic structure, housing and urbanisation.27 Peer groups were created using a non-hierarchical cluster analysis using 23 variables from the 2021 Canadian Census; key variables for clustering included: Indigenous identity, population density, proportion of immigrants arriving between 2011 and 2021, average dwelling value and long-term unemployment rate.27 Peer groups E and I are the nearest neighbour clusters of all nine peer groups, suggesting a high level of similarity between health regions within the two groups.27 Technical details on peer group classifications have been published elsewhere.27
Intervention
Based on our environmental scan, we identified PHUs that issued a recommendation to rescreen all pregnant persons for syphilis during pregnancy. Ontario PHUs are designed to meet the needs of specific geographic designations (ie, municipalities, townships, districts, counties and/or cities); the Statistics Canada Postal Code Conversion File Plus (PCCF+) is commonly used to assign postal codes to Census dissemination areas within PHU boundaries.31 32 The PCCF+ was used to assign screened individuals to either intervention or control PHUs based on their residential postal code indicated on the test requisition at the time of prenatal testing. Four of the nine PHUs adopted universal rescreening recommendations between 2019 and 2023; PHUs were considered first exposed to the policy change in the month following adoption. Online supplemental figure S2 illustrates staggered adoption of recommendations across PHUs. The environmental scan captured how PHUs communicated rescreening recommendations to healthcare providers within their jurisdictions. The remaining five PHUs did not change recommendations, which aligned with Canadian guidelines (one screen for all pregnant people in the first trimester or at the initial prenatal visit) throughout the study period and formed the control comparison group.
Outcome
The primary outcome of interest was the overall monthly prenatal syphilis screening rate, calculated as the number of laboratory-performed CMIA screening tests conducted per PHU per month divided by the estimated number of pregnancies per PHU per month.
Statistical analysis
Maternal age (5-year intervals) and neighbourhood-level social determinants of health were summarised for tested individuals in intervention and control PHUs, before and after the adoption of rescreening recommendations. We used a difference-in-differences (DiD) approach to estimate the impact of adopting universal prenatal syphilis rescreening recommendations at the PHU level. This quasi-experimental method allowed us to compare changes in screening rates over time between intervention and control PHUs, isolating the effect of the policy change from secular trends.33 To account for multiple groups and staggered policy adoption in our study, we employed the analytical approach developed by Callaway and Sant’Anna.34 35 This approach estimated group-time average treatment (policy) effects using PHUs not exposed to policy changes as controls; the group-time average policy effects were aggregated across intervention PHUs to estimate the average effect of adopting prenatal syphilis rescreening recommendations during the study period.35 We also present group-specific estimates.34 35 We implemented the approach using the did package in R; doubly robust estimation was used, and standard errors were clustered to the PHU level using the multiplier bootstrap.34 36 Additional details on the DiD approach can be found in online supplemental appendix 2. As standard practice, we assessed the parallel trends assumption for the DiD design, graphically, by inspecting preintervention prenatal syphilis screening rates, and statistically, by evaluating whether preintervention prenatal syphilis screening rates differed significantly between intervention groups.33
All analyses were performed using R V.4.5.2.37
Patient and public involvement
Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of our research.
Results
Stage I
28 of Ontario’s 34 PHUs responded to the survey (82% response rate), representing all Ontario health regions (online supplemental figure S3). Respondents included public health decision-makers (13%), upper-level/middle-level managers of sexual health or infectious disease programmes (50%), and registered public health nurses (38%). Overall, survey respondent PHUs were broadly representative of all Ontario PHUs (table 1). As of December 2023, 10 of the 28 participating PHUs (36%) reported recommending two or three universal prenatal syphilis screens per pregnancy, 17 (61%) followed Canadian guidelines recommending a single universal screen, and one PHU (4%) had no specific local recommendations. PHUs that recommended universal rescreening had significantly higher average annual rates of infectious syphilis among females aged 15–49, from 2021 to 2023, and early congenital syphilis, from 2019 onwards, compared with PHUs following standard universal screening guidelines.
Table 1. Landscape of prenatal syphilis screening across Ontario public health units.
| Sample characteristic* | Ontario (n=34 PHUs) |
Survey respondents (n=28 PHUs) |
Universal rescreening† (n=10 PHUs) |
Universal screening‡ (n=18 PHUs) |
||||
|---|---|---|---|---|---|---|---|---|
| Syphilis epidemiology | ||||||||
| Average annual infectious syphilis rate in females aged 15–49 per 100 000 population (total number of cases) | ||||||||
| 2018 | 2.8 | (92) | 1.7 | (77) | 2.0 | (17) | 1.5 | (60) |
| 2019 | 4.5 | (150) | 3.0 | (127) | 2.5 | (18) | 3.3 | (109) |
| 2020 | 6.6 | (222) | 5.0 | (186) | 5.3 | (40) | 4.9 | (146) |
| 2021 | 12.7 | (426) | 12.6 | (374) | 20.4 | (136) | 8.3 | (238) |
| 2022 | 15.5 | (538) | 17.7 | (463) | 31.1 | (174) | 10.2 | (289) |
| 2023 | 15.1 | (546) | 21.2 | (479) | 34.7 | (176) | 13.7 | (303) |
| Average early congenital syphilis rate per 100 000 live births (total number of cases) | ||||||||
| 2018 | 0.7 | (1) | 0.6 | (1) | 0.0 | (0) | 1.0 | (1) |
| 2019–2022 | 7.6 | (41) | 12.4 | (38) | 20.0 | (15) | 8.1 | (23) |
| 2023§ | 9.7 | (13) | 12.5 | (10) | 29.5 | (6) | 3.0 | (4) |
| Demographics | ||||||||
| Ontario health region | ||||||||
| Central East or Toronto | 7 | (21%) | 5 | (18%) | 1 | (8%) | 4 | (25%) |
| Central West | 7 | (21%) | 6 | (21%) | 3 | (25%) | 3 | (19%) |
| Eastern | 6 | (18%) | 6 | (21%) | 1 | (8%) | 5 | (31%) |
| North West or North East | 7 | (21%) | 6 | (21%) | 3 | (25%) | 3 | (19%) |
| South West | 7 | (21%) | 5 | (18%) | 2 | (17%) | 3 | (19%) |
| Urban/rural region | ||||||||
| Large urban | 5 | (15%) | 5 | (18%) | 0 | (0%) | 5 | (28%) |
| Urban | 6 | (18%) | 6 | (21%) | 3 | (30%) | 3 | (17%) |
| Urban-rural | 18 | (53%) | 13 | (46%) | 5 | (50%) | 8 | (44%) |
| Northern or rural | 5 | (15%) | 4 | (14%) | 2 | (20%) | 2 | (11%) |
| PHU organisational structure¶ | ||||||||
| Autonomous | 24 | (71%) | 18 | (64%) | 8 | (80%) | 10 | (56%) |
| Prenatal syphilis screening practices | ||||||||
| Universal screening recommendations** | ||||||||
| First trimester (or initial prenatal visit) | -- | -- | 17 | (61%) | 0 | (0%) | 17 | (94%) |
| First trimester and at mid-gestation | -- | -- | 2 | (7%) | 2 | (20%) | 0 | (0%) |
| First trimester and at delivery | -- | -- | 1 | (4%) | 1 | (10%) | 0 | (0%) |
| First trimester, mid-gestation and at delivery | -- | -- | 7 | (25%) | 7 | (70%) | 0 | (0%) |
| None specified | -- | -- | 1 | (4%) | 0 | (0%) | 1 | (6%) |
| Promotion of risk-based screening | -- | -- | 24 | (86%) | 9 | (90%) | 15 | (83%) |
| Implementation of strategies to increase prenatal syphilis screening uptake | -- | -- | 20 | (71%) | 8 | (80%) | 12 | (67%) |
| Reasons (rescreening) or anticipated reasons (screening) for recommending universal rescreening | ||||||||
| Local syphilis epidemiology | -- | -- | 22 | (79%) | 9 | (90%) | 13 | (72%) |
| Neighbouring PHU syphilis epidemiology | -- | -- | 12 | (43%) | 5 | (50%) | 7 | (39%) |
| Provincial syphilis epidemiology | -- | -- | 16 | (57%) | 8 | (80%) | 8 | (44%) |
| National syphilis epidemiology | -- | -- | 14 | (50%) | 9 | (90%) | 5 | (28%) |
| Screening guidelines or guidance | -- | -- | 7 | (25%) | 1 | (10%) | 6 | (33%) |
Variable distributions are reported as n (%) unless otherwise specified.
PHUs recommending two or more prenatal syphilis screens for all pregnant persons (as of December 2023).
PHUs recommending one prenatal syphilis screen for all pregnant persons (following Canadian guidelines).
Rates for 2023 for nine PHUs were based on live birth data from 2022.
Autonomous PHUs operate independently from any municipality; non-autonomous PHUs are integrated into the administrative structure of a municipality.24
Recommendations as of December 2023.
PHU, public health unit.
There was a shift in recommendations between 2018 and 2023 (figure 1). In 2018, five PHUs recommended two screens per pregnancy, and none recommended three screens per pregnancy. By 2023, seven PHUs were recommending three universal screens per pregnancy with an additional three recommending two universal screens per pregnancy (figure 1). The proportion of PHUs promoting risk-based screening and those implementing at least one strategy to increase prenatal syphilis screening uptake was similar between PHUs recommending rescreening and those following standard screening (table 1). We found that PHUs recommending universal rescreening tended to adopt a broader set of risk-based screening criteria and use more strategies to promote prenatal syphilis screening uptake (online supplemental table S1). Among PHUs recommending universal rescreening, the most common drivers for adoption included changes in syphilis epidemiology at the local, national and provincial levels (table 1). While most PHUs not recommending rescreening also cited evolving syphilis epidemiology at the local level as an anticipated reason to change policy, one-third indicated that updates to formal screening guidelines or guidance would be necessary.
Figure 1. Adoption of universal prenatal syphilis rescreening recommendations by Ontario public health units, 2018–2023. Universal rescreening includes ≥2 syphilis tests during pregnancy (eg, at mid-gestation and/or delivery, in addition to first trimester screening).
Three overarching themes, based on 36 open-ended survey responses from 21 PHUs, were identified through thematic analysis and highlight both the opportunities and challenges in scaling up universal prenatal syphilis rescreening across Ontario (online supplemental table S2). Facilitators to enhancing universal prenatal syphilis screening included subthemes such as the importance of clear direction or guidance from provincial or national authorities, and a general openness among some PHUs to adapt practices in response to evolving syphilis epidemiology. Barriers to prenatal syphilis screening and prevention included concerns about limited access to prenatal care and strained primary care resources, as well as the need for increased education among healthcare providers and community members. Variation in PHU scope reflected differences in perceived responsibilities related to prenatal screening and infectious disease prevention, as well as variability in the extent to which PHUs actively promote prenatal syphilis screening.
Stage II
A total of 58 886 CMIA screens were conducted on prenatal specimens from 42 535 pregnant individuals aged 15 to 49 years across the nine PHUs from 2019 to 2023. After applying the eligibility criteria, 58 103 CMIA screening records from 42 227 pregnant individuals were included in the analysis, with 28 887 records from intervention PHUs and 29 216 from control PHUs (online supplemental figure S4). Neighbourhood-level social determinants of health data were missing for 2.8% (n=1618) of the final study population due to limitations in census coverage.
Overall, based on neighbourhood-level indicators of social determinants of health, the individuals screened were somewhat more marginalised in terms of material resources and lived in areas with fewer racialised and newcomer populations than the province of Ontario (table 2). Observed characteristics were similar between screened individuals in the intervention and control PHUs during the preintervention period, except for individuals in the intervention group having higher levels of marginalisation related to racialised and newcomer populations (table 2). In the postintervention period, tested individuals in the intervention group were somewhat more marginalised in the racialised and newcomer populations dimension.
Table 2. Characteristics of tested individuals, stratified by assignment to public health units that did (intervention) or did not (control) recommend universal prenatal syphilis rescreening.
| Sample characteristics* | Intervention (universal rescreening) | Control (universal screening‡) | ||||||
|---|---|---|---|---|---|---|---|---|
| Preintervention (n=22 703 tests) |
Postintervention (n=6184 tests) |
Preintervention (n=22 903 tests) |
Postintervention (n=6313 tests) |
|||||
| Demographics | ||||||||
| Maternal age, years | ||||||||
| 15–19 | 649 | (3%) | 126 | (2%) | 646 | (3%) | 178 | (3%) |
| 20–24 | 2874 | (13%) | 642 | (10%) | 3545 | (16%) | 874 | (14%) |
| 25–29 | 7186 | (32%) | 1871 | (30%) | 7862 | (34%) | 2030 | (32%) |
| 30–34 | 7830 | (35%) | 2263 | (37%) | 7359 | (32%) | 2147 | (34%) |
| 35–39 | 3495 | (15%) | 1049 | (17%) | 2948 | (13%) | 904 | (14%) |
| 40–44 | 639 | (3%) | 222 | (4%) | 508 | (2%) | 170 | (3%) |
| 45–49 | 30 | (<1%) | 11 | (<1%) | 35 | (<1%) | 10 | (<1%) |
| Material resources | ||||||||
| Quintile 1 (least marginalised) | 3177 | (14%) | 1002 | (16%) | 4340 | (19%) | 1189 | (19%) |
| Quintile 2 | 4330 | (19%) | 1384 | (22%) | 4106 | (18%) | 1111 | (18%) |
| Quintile 3 | 4125 | (18%) | 1206 | (20%) | 4413 | (19%) | 1192 | (19%) |
| Quintile 4 | 4734 | (21%) | 1088 | (18%) | 4148 | (18%) | 1134 | (18%) |
| Quintile 5 | 5449 | (24%) | 1436 | (23%) | 5373 | (24%) | 1548 | (25%) |
| Missing | 888 | (4%) | 68 | (1%) | 523 | (2%) | 139 | (2%) |
| Racialised and newcomer populations | ||||||||
| Quintile 1 (least marginalised) | 8651 | (38%) | 1999 | (32%) | 11 540 | (50%) | 3184 | (50%) |
| Quintile 2 | 6797 | (30%) | 1747 | (28%) | 7455 | (33%) | 1960 | (31%) |
| Quintile 3 | 4902 | (22%) | 1635 | (26%) | 2724 | (12%) | 861 | (14%) |
| Quintile 4 | 1330 | (6%) | 671 | (11%) | 546 | (2%) | 150 | (2%) |
| Quintile 5 | 135 | (1%) | 64 | (1%) | 115 | (1%) | 19 | (<1%) |
| Missing | 888 | (4%) | 68 | (1%) | 523 | (2%) | 139 | (2%) |
Variable distributions are reported as n (%).
Recommending two or more prenatal syphilis screens for all pregnant persons.
Recommending one prenatal syphilis screen for all pregnant persons.
Intervention PHUs were followed for a median of 48 months (IQR: 47–52) before the adoption of universal rescreening and 11 months (IQR: 7–12) after adoption (figure 2a). Following the examination of the parallel trends assumption (online supplemental figure S5 and table S3), on average, prenatal syphilis screening rates increased by 375.5 tests per month per 1000 pregnancies (95% CI 320.7 to 430.3) postadoption across intervention PHUs (table 3). There was heterogeneity in screening rates across the four intervention PHUs (figure 2; table 3). PHU 1 showed fluctuation with a moderate increase in screening rates of 139.6 tests per month per 1000 pregnancies (95% CI 36.4 to 242.9). PHU 2 had an immediate and sustained effect with an increase of 1162.7 tests per month per 1000 pregnancies (95% CI 1049.5 to 1275.9). PHU 3 had a lagged but moderate rise of 199.9 more tests per month per 1000 pregnancies (95% CI 149.8 to 250.1). PHU 4 showed no significant change in screening rates following adoption. When comparing implementation practices between intervention PHUs, PHU 2 implemented the most comprehensive dissemination approach, including communicating changes to the widest range of healthcare providers and community partners, using the highest number of communication channels, and was the only PHU with a process to actively monitor implementation of recommendations (online supplemental table S4). Intervention PHUs 1, 2 and 4 reported challenges during implementation (online supplemental table S4).
Figure 2. Prenatal syphilis screening tests per 1000 pregnancies. (a) Screening rates in intervention PHUs (n=4) compared with the average of control PHUs (n=5). Vertical dashed lines indicate staggered adoption of universal rescreening recommendations. Trends are smoothed using locally estimated scatterplot smoothing; data for December 2022 were unavailable. (b) Average PHU-specific change in screening rates following policy adoption in intervention PHUs relative to controls. PHU, public health unit.
Table 3. Difference-in-differences model estimates for monthly prenatal syphilis screening tests performed per 1000 pregnancies*.
| Monthly number of tests | 95% CI† | |
|---|---|---|
| Overall average policy effect | 375.5 | 320.7 to 430.3 |
| Group effects | ||
| Intervention PHU 1 | 139.6 | 36.4 to 242.9 |
| Intervention PHU 2 | 1162.7 | 1049.5 to 1275.9 |
| Intervention PHU 3 | 199.9 | 149.8 to 250.1 |
| Intervention PHU 4 | −0.3 | −83.8 to 83.2 |
The model was specified usingPHUs not exposed to policy changes as control group, no anticipation periods, doubly robust estimation and cluster-robust SEs to account for clustering at the PHU level. The overall average policy effect is based on PHU aggregation. Group effects represent PHU-specific average policy effects.
95% pointwise confidence bands are presented for group-specific estimates.
PHU, public health unit.
Discussion
This study offers the first provincial-level examination of prenatal syphilis screening practices in Ontario during a period of rapidly evolving syphilis epidemiology. We observed substantial heterogeneity across Ontario’s PHUs in terms of screening recommendations, implementation strategies and universal rescreening uptake. Several PHUs emphasised the need for clearer and more consistent guidance from provincial or national authorities, underscoring the importance of top-down policy leadership to enable timely and coordinated public health responses. While heightened awareness of changing epidemiology facilitated changes in local recommendations, this did not consistently translate into increased prenatal syphilis screening by providers, with marked variability across intervention PHUs. Together, these findings emphasise that the impact of public health policy depends not only on adoption but also on how policies are implemented in practice.
The burden of congenital syphilis remains a critical concern for global neonatal health, and data from the WHO has identified it as the second leading cause of preventable stillbirth worldwide.3 Resurgences of congenital syphilis have occurred in high-income countries, including those with publicly funded universal healthcare access, despite long-standing prenatal screening recommendations, effective treatment strategies and case management protocols.38 39 In Canada, the national public health agency guides clinicians on prenatal syphilis screening as well as treatment and follow-up for syphilis in pregnancy; the Canadian Paediatric Society has outlined recommendations for the care of infants with congenital syphilis and syphilis-exposed infants.10 40 Rises in congenital syphilis in high-resourced settings, such as Canada and the USA, have been attributed to missed opportunities for prevention in prenatal care pathways and systemic inequities linked to structural and social determinants of health.38 39 Routine rescreening for syphilis during pregnancy can reduce the risk of undetected seroconversion, facilitate the diagnosis of infections or re-infections later in pregnancy, and ensure that infections are not missed in pregnant individuals without identifiable risk factors.11 12 19 20 The recommendation of routine rescreening has become a common public health strategy across various high-income jurisdictions. Notable examples include Australia replacing a single universal first-visit screen with three universal screenings (first prenatal visit, 26–28 weeks and 36 weeks or at birth) at the national level in 2024.41 Additionally, universal rescreening has been increasingly incorporated into US state laws and Canadian provincial and territorial screening guidelines over time.1 15 17 Similarly, we observed increased adoption of rescreening recommendations across Ontario PHUs between 2018 and 2023.
The utility of population-level screening interventions largely depends on effective implementation. Previous studies examining adherence to universal rescreening guidelines have shown limited changes in screening rates. Among eight studies measuring adherence to recommendations for routine rescreening in Canada or the USA, seven found between 4% and 29% of pregnant people received recommended screens at appropriate time points, and one study reported 79% adherence.916 18,21 42 43 In comparison, we examined changes in screening volume rather than adherence. Our use of a control group within our quasi-experimental design enabled us to account for secular changes and identify the significant impact of changing recommendations on prenatal syphilis screening rates in Ontario PHUs.
Research from the USA has revealed varied screening practices among racialised populations, such as lower screening rates due to inadequate prenatal care access or higher rates resulting from risk profiling.9 16 20 42 In our study, tested individuals in intervention PHUs had a higher proportion of neighbourhood-level racialised and newcomer populations marginalisation before policy implementation, with this difference increasing somewhat postimplementation. This could suggest that universal rescreening policies helped improve access for individuals living in areas with higher proportions of racialised and newly migrated populations; however, it may also reflect provider-driven profiling. Further research is needed to assess whether this trend represents equity-oriented outreach or differential application of screening practices.
We found considerable heterogeneity across PHUs regarding their perceived responsibility and scope with respect to syphilis screening in pregnancy. The Ontario Public Health Standards define a broad mandate for local PHUs; differences in geography (from large urban centres to rural northern communities), populations served, local governance structures and resource availability may contribute to additional variation in PHU activities.24 44 Belon et al found that more robust health equity programme implementation approaches were observed in urban areas compared with rural areas across Ontario.44 Variability in programme implementation was attributed to differences in infrastructure and capacity, with more limitations for small and rural PHUs.44 In contrast, we observed adoption of universal rescreening recommendations in urban, urban–rural and northern or rural, but not large urban PHUs. This could suggest that local needs or concerns surrounding shifting syphilis epidemiology could supersede resource or capacity constraints in smaller or rural PHUs. Differences in governance and lack of provincial guidance have also been identified as potential contributors to observed variation in PHU activity.44 45 We found that top-down influences, specifically a lack of national or provincial guidance, characterised the differing practices of PHUs.
Although we found a significant increase in monthly prenatal syphilis screening rates following adoption of universal rescreening recommendations, there was substantial heterogeneity across intervention PHUs. Similar regional variations in prenatal syphilis screening rates have been observed in other settings.11 18 In our study, all PHUs (irrespective of adopting rescreening recommendations) experienced substantial increases in infectious syphilis rates between 2019 and 2023—that is, at least a 100% increase.46 Intervention PHUs 1 and 3 recommended increasing from two to three tests and experienced moderate changes in screening; this preimplementation policy could have resulted in a smaller relative change in screening compared with PHU 2 which recommended increasing from one to three tests. However, as the magnitude of preintervention screening rates was similar across all intervention PHUs, we expect that the impact of differences in prepolicies would have been minimal. We believe that the change in prenatal syphilis screening rates in our study are mainly attributable to variations in implementation strategies and infrastructure between PHUs. Notably, PHU 2, which experienced the most significant and sustained increase in screening, reported the most comprehensive implementation strategy and was the only PHU with a mechanism in place to monitor implementation. Intervention PHUs 1 and 4 experienced moderate and no changes in screening rates, respectively, and cited a lack of resources to conduct testing as a challenge to implementation. Both these PHUs are located in rural areas and prior research has observed that Ontario PHUs serving rural or sparsely populated communities may face structural barriers to developing and/or implementing public health programmes, such as limited resource availability.44 Limited provider knowledge of syphilis infections or screening recommendations, also previously observed among US providers,9 47 and client loss to follow-up were identified as additional challenges to implementation. Continuing medical education serves as an important platform to expand physician familiarity with evolving public health issues and systematic promotion of educational resources within primary and maternal care networks could improve provider adherence to recommendations and contribute to control of the ongoing syphilis epidemic.
Globally, researchers have investigated other approaches to improve syphilis disease prevention and control, including initiatives to support public health infrastructure, mass education campaigns to expand public awareness, and behavioural interventions to improve prenatal screening coverage.48,51 Regions facing a resurgence of infectious syphilis and congenital syphilis can learn from countries like Brazil, where national roll-out of targeted public health efforts, including the adoption of point-of-care testing (POCT), contributed to a reduction in syphilis rates.48 49 52 POCT has the potential to improve testing and treatment coverage among underserved populations, including pregnant persons, facing barriers accessing traditional care pathways.53,55 While the first POCT was approved for use in Canada in March 2023, adoption has been limited.53 Overall, population-level control of infectious syphilis and prevention of congenital syphilis will require widespread, multipronged interventions.
A main strength of this study was the use of an iKT approach that prioritised relevance for public health decision-makers. The combination of a quasi-experimental design with an environmental scan provided both quantitative evidence of policy effectiveness and qualitative insight into the drivers and barriers to adoption and implementation. Finally, by using a robust DiD analysis, accounting for multiple groups and staggered adoption, we were able to examine changes in screening rates while accounting for secular trends during a period of dynamic syphilis epidemiology.
Several limitations must also be acknowledged. First, we were unable to quantify the proportion of pregnant individuals who did not receive any prenatal syphilis screening. Laboratory serology data were not linked to birth admission records, which limited our ability to distinguish pregnancies, assess trimester-specific screening timing and statistically account for repeated observations at the individual level. Additionally, while the vast majority of CMIA screening is conducted at the provincial public health laboratory, a small proportion of specimens (<1%) may have been sent to other laboratories (to which we did not have access). Postal codes are not a perfect measure of assignment to PHUs, as not all postal codes, particularly those in rural areas, respect geographic boundaries; however, we would expect the likelihood of misclassification to PHUs to be minimal. We had limited postintervention follow-up time for some intervention PHUs, which may mean insufficient follow-up to assess sustained changes in screening rates. We also acknowledge that certain assumptions (exchangeability, consistency and positivity) of our DiD analysis must be met for causal inference.56 However, in practice, the roll-out of public health policies and programmes most often occurs in response to a growing or pressing need and seldom meets the criteria for causal inference. Quasi-experimental approaches are often applied to the study of public health interventions and allow for a more robust estimate of the intervention’s impact than other designs.57 58 Furthermore, our findings are likely more generalisable to areas with similar resources and geographic characteristics to those of our study population. Finally, while the focus of this work was on the adoption of repeat screening among PHUs in Ontario, we recognise the clinical utility of understanding the impact of such recommendations on improving diagnosis of syphilis in pregnancy to minimise risks of vertical transmission; future studies should explore the effectiveness of universal rescreening recommendations on clinical outcomes over a longer follow-up period.
In response to local syphilis outbreaks and rising rates of congenital syphilis, several Ontario PHUs independently implemented universal rescreening strategies with considerable variability in uptake. These findings underscore the importance of not only adopting evidence-informed policies, but also investing in implementation infrastructure and leadership, as without adequate uptake, the population-level benefits of universal prenatal syphilis rescreening will be limited. PHUs may need to incorporate deliberate strategies such as targeted provider education, intersectoral collaboration and ongoing monitoring systems, in order to effectively translate policy into meaningful public health outcomes.
Supplementary material
Acknowledgements
This work would not have been possible without access to syphilis serology data from Public Health Ontario. The authors thank participating Ontario public health unit staff for their time and contributions. Grammarly was used by some authors during the review and editing of this work. Elements of this work were previously presented at three national conferences in Canada.
The funder had no role in the study design, data collection, analysis or interpretation, nor in the writing of the report or the decision to submit the paper for publication. Parts of this material are based on data provided by Public Health Ontario. No endorsement by Public Health Ontario is intended or should be inferred. Parts of this material are based on publicly available information compiled and adapted from Statistics Canada. This does not constitute an endorsement by Statistics Canada of this study.
Footnotes
Funding: This work was supported by the Canadian Institutes of Health Research (CIHR) through a Catalyst Grant (STBBI Research in Canada: Beyond HIV/AIDS and Hepatitis C; Application No. 523705; Competition Code 202405SRC; Funding Reference No. SR7 – 196517) awarded to SS (NPA). AF received a CIHR Canada Graduate Scholarship–Master’s (CGS-M) program award (grant/award number: not applicable).
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Not applicable.
Ethics approval: This study was approved by the Health Sciences and Affiliated Teaching Hospitals Research Ethics Board at Queen’s University (HSREB #6041941; HSREB #6040819). All survey participants provided informed consent.
Data availability free text: Specimen level line-list prenatal syphilis testing data may be available on request to Public Health Ontario, an agency of the Government of Ontario. Survey data are not available to be released due to respondent/public health unit privacy and confidentiality.
Map disclaimer: The depiction of boundaries on this map does not imply the expression of any opinion whatsoever on the part of BMJ (or any member of its group) concerning the legal status of any country, territory, jurisdiction or area or of its authorities. This map is provided without any warranty of any kind, either express or implied.
Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Data availability statement
Data may be obtained from a third party and are not publicly available.
References
- 1.Aho J, Lybeck C, Tetteh A, et al. Rising syphilis rates in Canada, 2011-2020. Can Commun Dis Rep . 2022;48:52–60. doi: 10.14745/ccdr.v48i23a01. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Dionisopoulos Z, Kakkar F, Blanchard AC. Delayed diagnosis of maternal and congenital syphilis: An unrecognized epidemic? Can Commun Dis Rep. 2022;48:115–8. doi: 10.14745/ccdr.v48i23a10. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.World Health Organization Global Sexually Transmitted Infections Programme: Mother-to-child transmission of syphilis. [-Dec-2025]. https://www.who.int/teams/global-hiv-hepatitis-and-stis-programmes/stis/prevention/mother-to-child-transmission-of-syphilis Available. Accessed.
- 4.Moseley P, Bamford A, Eisen S, et al. Resurgence of congenital syphilis: new strategies against an old foe. Lancet Infect Dis. 2024;24:e24–35. doi: 10.1016/S1473-3099(23)00314-6. [DOI] [PubMed] [Google Scholar]
- 5.Moore A, Freyne B, Nourse C. The Global Crisis of Congenital Syphilis: Vulnerable and Disenfranchised Women Most at Risk. RRN. 2023;13:65–79. doi: 10.2147/RRN.S428322. [DOI] [Google Scholar]
- 6.Pan American Health Organization (PAHO) Technical note: Guidance for the elimination of syphilis and congenital syphilis in the Americas. 2024. [-Jun-2025]. https://iris.paho.org/bitstream/handle/10665.2/61824/PAHOCDEHT240014_eng.pdf?sequence=1&isAllowed=y Available. Accessed.
- 7.Pan American Health Organization (PAHO) Belize, Jamaica and St. Vincent and the Grenadines eliminate mother-to-child transmission of HIV and syphilis. 2024. [-Jun-2025]. https://www.paho.org/en/news/7-5-2024-belize-jamaica-and-st-vincent-and-grenadines-eliminate-mother-child-transmission-hiv Available. Accessed.
- 8.The Public Health Agency of Canada . Canadian Communicable Disease Report; 2025. Infectious syphilis and congenital syphilis in Canada, 2023; p. 51-2/3. [Google Scholar]
- 9.Trepka MJ, Bloom SA, Zhang G, et al. Inadequate syphilis screening among women with prenatal care in a community with a high syphilis incidence. Sex Transm Dis . 2006;33:670–4. doi: 10.1097/01.olq.0000216032.52731.ea. [DOI] [PubMed] [Google Scholar]
- 10.Public Health Agency of Canada Sexually transmitted and blood-borne infection guides: syphilis. [-Aug-2025]. https://www.canada.ca/en/public-health/services/infectious-diseases/sexual-health-sexually-transmitted-infections/canadian-guidelines/syphilis.html Available. Accessed.
- 11.Schrag SJ, Arnold KE, Mohle-Boetani JC, et al. Prenatal screening for infectious diseases and opportunities for prevention. Obstet Gynecol . 2003;102:753–60. doi: 10.1016/s0029-7844(03)00671-9. [DOI] [PubMed] [Google Scholar]
- 12.McDonald R, O’Callaghan K, Torrone E, et al. Vital Signs: Missed Opportunities for Preventing Congenital Syphilis - United States, 2022. MMWR Morb Mortal Wkly Rep . 2023;72:1269–74. doi: 10.15585/mmwr.mm7246e1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Rahman MM-U, Hoover A, Johnson C, et al. Preventing Congenital Syphilis-Opportunities Identified by Congenital Syphilis Case Review Boards. Sex Transm Dis . 2019;46:139–42. doi: 10.1097/OLQ.0000000000000909. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.The American College of Obstetricians and Gynecologists (ACOG) Practice advisory – Screening for syphilis in pregnancy. 2024. [-Jun-2025]. https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2024/04/screening-for-syphilis-in-pregnancy Available. Accessed.
- 15.Centers for Disease Control and Prevention: Division of STD Prevention State statutory and regulatory language regarding prenatal syphilis screenings in the United States. 2024. [-Jun-2025]. https://www.cdc.gov/syphilis/media/pdfs/2024/07/Prenatal-Syphilis-Screening-Laws-Web-Document-25-July-2024-final.pdf Available. Accessed.
- 16.Clement AC, Fay KE, Yee LM. Disparities in state-mandated third-trimester testing for syphilis. Am J Obstet Gynecol MFM. 2022;4:100595. doi: 10.1016/j.ajogmf.2022.100595. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Ontario Agency for Health Protection and Promotion (Public Health Ontario) Evidence brief: Universal prenatal syphilis screening and congenital syphilis. 2023. [-Jun-2025]. https://www.publichealthontario.ca/-/media/Documents/U/2023/universal-prenatal-screening-congenital-syphilis.pdf?rev=dd1dc37fd58441b0b882bc320f10d9a5&sc_lang=en Available. Accessed.
- 18.Shaw S, Plourde P, Klassen P, et al. A descriptive study of syphilis testing in Manitoba, Canada, 2015-2019. Can Commun Dis Rep . 2022;48:95–101. doi: 10.14745/ccdr.v48i23a07. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Plitt SS, Osman M, Sahni V, et al. Examination of a prenatal syphilis screening program, Alberta, Canada: 2010-2011. Can J Public Health. 2016;107 doi: 10.17269/CJPH.107.5320. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Dude AM, Drexler K, Yee LM, et al. Adherence to Sexually Transmitted Infection Screening in Pregnancy. J Womens Health (Larchmt) 2023;32:652–6. doi: 10.1089/jwh.2022.0409. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Wilson EK, Gavin NI, Adams EK, et al. Patterns in prenatal syphilis screening among Florida Medicaid enrollees. Sex Transm Dis . 2007;34:378–83. doi: 10.1097/01.olq.0000245908.23629.b8. [DOI] [PubMed] [Google Scholar]
- 22.Martin D, Miller AP, Quesnel-Vallée A, et al. Canada’s universal health-care system: achieving its potential. Lancet. 2018;391:1718–35. doi: 10.1016/S0140-6736(18)30181-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Statistics Canada Table 17-10-0009-01 Population estimates, quarterly. n.d. Available. [DOI]
- 24.Smith RW, Allin S, Rosella L, et al. Profiles of public health systems in Canada: Ontario. 2021. [-May-2025]. https://ccnpps-ncchpp.ca/docs/2021-Profiles-of-Public-Health-Systems-in-Canada-Ontario.pdf Available. Accessed.
- 25.Ontario Ministry of Health and Long-Term Care Ontario Public Health Standards: Requirements for Programs, Services and Accountability. 2021. [-May-2025]. https://files.ontario.ca/moh-ontario-public-health-standards-en-2021.pdf Available. Accessed.
- 26.Public Health Ontario Easy Maps v2.0. https://www.publichealthontario.ca/en/data-and-analysis/commonly-used-products/maps/easy-map n.d. Available.
- 27.Statistics Canada Health region peer groups – Working paper, 2023. Catalogue no. 82-622-X. 2024. Reproduced and distributed on an “as is” basis with the permission of Statistics Canada. [-May-2025]. https://www150.statcan.gc.ca/n1/en/pub/82-622-x/82-622-x2024001-eng.pdf?st=6Cp4yOQh Available. Accessed.
- 28.Nowell LS, Norris JM, White DE, et al. Thematic Analysis: Striving to Meet the Trustworthiness Criteria. Int J Qual Methods. 2017;16:1609406917733847. doi: 10.1177/1609406917733847. [DOI] [Google Scholar]
- 29.Public Health Ontario Syphilis – Serology. [-Jul-2025]. https://www.publichealthontario.ca/en/Laboratory-Services/Test-Information-Index/Syphilis-Serology#:~:text=Testing%20Indications&text=Screening%20is%20recommended%20for%20individuals,with%20ongoing%20or%20high%20risk Available. Accessed.
- 30.Matheson FI, Moloney G, van Ingen T. Joint Publication with Public Health Ontario; 2023. [-May-2025]. 2021 Ontario marginalization index: user guide. St. Michael’s Hospital (Unity Health Toronto)https://www.publichealthontario.ca/-/media/documents/o/2017/on-marg-userguide.pdf Available. Accessed. [Google Scholar]
- 31.Ontario Agency for Health Protection and Promotion (Public Health Ontario) Toronto, ON: Queen’s Printer for Ontario; 2018. Small area analysis: A primer for public health units.https://www.publichealthontario.ca/-/media/documents/S/2018/saa-guidance.pdf Available. [Google Scholar]
- 32.Statistics Canada Data from: Statistics Canada Postal Code Conversion File Plus (PCCF +) version 8B
- 33.Saeed S, Moodie EEM, Strumpf EC, et al. Evaluating the impact of health policies: using a difference-in-differences approach. Int J Public Health . 2019;64:637–42. doi: 10.1007/s00038-018-1195-2. [DOI] [PubMed] [Google Scholar]
- 34.Callaway B, Sant’Anna PHC. Difference-in-Differences with multiple time periods. J Econom. 2021;225:200–30. doi: 10.1016/j.jeconom.2020.12.001. [DOI] [Google Scholar]
- 35.Callaway B, Sant’Anna PHC. Introduction to DiD with Multiple Time Periods. [-Dec-2025]. https://bcallaway11.github.io/did/articles/multi-period-did.html Available. Accessed.
- 36.Callaway B, Sant’Anna PHC. Difference-in-differences methods: Group-time average treatment effects. [-Dec-2025]. https://bcallaway11.github.io/did/reference/att_gt.html Available. Accessed.
- 37.R Core Team . Vienna, Austria: R Foundation for Statistical Computing; 2024. R: A language and environment for statistical computing.https://www.R-project.org/ Available. [Google Scholar]
- 38.Singh AE, Wong T, Robinson J. Syphilis screening in pregnancy: no time for complacency. Curr Opin Obstet Gynecol . 2025;37:332–9. doi: 10.1097/GCO.0000000000001049. [DOI] [PubMed] [Google Scholar]
- 39.Zink AB, McCann NC, Walensky RP. From Crisis to Action - Policy Pathways to Reverse the Rise in Congenital Syphilis. N Engl J Med . 2025;393:2388–91. doi: 10.1056/NEJMp2513438. [DOI] [PubMed] [Google Scholar]
- 40.Fanella S, Bitnun A, Barton M, et al. Diagnosis and management of congenital syphilis – Avoiding missed opportunities. 2024. [-Jun-2024]. https://cps.ca/en/documents/position/congenital-syphilis Available. Accessed. [DOI] [PMC free article] [PubMed]
- 41.Department of Health Victoria Changes to syphilis testing during pregnancy. 2025. [-Jun-2025]. https://www.health.vic.gov.au/health-advisories/congenital-syphilis-in-victoria Available. Accessed.
- 42.Fowler CI, Gavin NI, Adams EK, et al. Racial and ethnic disparities in prenatal syphilis screening among women with Medicaid-covered deliveries in Florida. Matern Child Health J . 2008;12:378–93. doi: 10.1007/s10995-007-0247-7. [DOI] [PubMed] [Google Scholar]
- 43.Liao C, Golden WC, Anderson JR, et al. Missed Opportunities for Repeat HIV Testing in Pregnancy: Implications for Elimination of Mother-to-Child Transmission in the United States. AIDS Patient Care STDS. 2017;31:20–6. doi: 10.1089/apc.2016.0204. [DOI] [PubMed] [Google Scholar]
- 44.Belon AP, Chew JL, Schwartz N, et al. Variability in public health programming and priorities to address health inequities across public health units in Ontario, Canada. Can J Public Health . 2024;115:813–24. doi: 10.17269/s41997-024-00896-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 45.Lyons J. The Independence of Ontario’s Public Health Units: Does Governing Structure Matter? Healthc Policy. 2016;12:71–83. doi: 10.12927/hcpol.2016.24777. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 46.Ontario Agency for Health Protection and Promotion (Public Health Ontario) Infectious syphilis and early congenital syphilis in Ontario: focus on 2022. 2024. [-Aug-2025]. https://www.publichealthontario.ca/-/media/Documents/S/2023/syphilis-ontario-focus-2022.pdf?rev=65558c76d7df4a13addbc19c16565dab&sc_lang=en#:~:text=Between%202020%20and%202022%2C%20eight Available. Accessed.
- 47.Collier MG, Taylor MM, Winscott MM, et al. Assessing compliance with a county board order for third trimester syphilis screening in Maricopa County, Arizona. Sex Reprod Healthc . 2011;2:125–8. doi: 10.1016/j.srhc.2011.05.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 48.Pinto R, Valentim R, Fernandes da Silva L, et al. Use of Interrupted Time Series Analysis in Understanding the Course of the Congenital Syphilis Epidemic in Brazil. Lancet Reg Health Am . 2022;7:100163. doi: 10.1016/j.lana.2021.100163. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 49.de Morais Pinto R, de Medeiros Valentim RA, Fernandes da Silva L, et al. Analyzing the reach of public health campaigns based on multidimensional aspects: the case of the syphilis epidemic in Brazil. BMC Public Health . 2021;21:1632. doi: 10.1186/s12889-021-11588-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 50.Cao G, Jing H, Jie C, et al. The changing epidemiology of syphilis: new strategies for new challenges in China. Lancet Reg Health West Pac. 2025;65:101752. doi: 10.1016/j.lanwpc.2025.101752. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 51.Althabe F, Chomba E, Tshefu AK, et al. A multifaceted intervention to improve syphilis screening and treatment in pregnant women in Kinshasa, Democratic Republic of the Congo and in Lusaka, Zambia: a cluster randomised controlled trial. Lancet Glob Health. 2019;7:e655–63. doi: 10.1016/S2214-109X(19)30075-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 52.Paiva JC de L, Dias-Trindade S, Gonzalez MOA, et al. Analysis of the Impact of Communication Campaigns under the Project “Syphilis No”: A National Tool for Inducing and Promoting Health. Int J Environ Res Public Health . 2022;19:15884. doi: 10.3390/ijerph192315884. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 53.Chittle AD, Sandstrom P, Cox J, et al. Treponemal point-of-care tests for syphilis. CMAJ . 2024;196:E702–3. doi: 10.1503/cmaj.231548. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 54.Eliopoulos A, Rivera B, McCullough E, et al. Performance of the bioLytical Multiplex HIV 1/2 and Syphilis rapid test on serum in a laboratory evaluation for syphilis. Microbiol Spectr. 2025;13:e00132-25. doi: 10.1128/spectrum.00132-25. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 55.Mackrell L, Carter M, Hoover M, et al. Syphilis Point of Care Rapid Test and Immediate Treatment Evaluation (SPRITE) study: a mixed-methods implementation science research protocol of eight public health units in Ontario, Canada. BMJ Open . 2024;14:e089021. doi: 10.1136/bmjopen-2024-089021. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 56.Hernán M, Robins J. Causal Inference: What If. Boca Raton: Chapman & Hall/CRC; 2020. [Google Scholar]
- 57.de Vocht F, Katikireddi SV, McQuire C, et al. Conceptualising natural and quasi experiments in public health. BMC Med Res Methodol . 2021;21:32. doi: 10.1186/s12874-021-01224-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 58.Centre for Epidemiology and Evidence . Sydney: NSW Ministry of Health; [-Dec-2025]. Study design for evaluating population health and health service interventions: A guide. 2023. Evidence and Evaluation Guidance Series, Population and Public Health Division.https://www.health.nsw.gov.au/research/Publications/study-design-guide.pdf Available. accessed. [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Data may be obtained from a third party and are not publicly available.