Syphilis clustering among young pregnant women in Kampala, Uganda

Introduction In Uganda, the spatial distribution of syphilis varies by age, gender, and region. Identifying clusters (subsets of administrative subdivisions) with high syphilis prevalence could boost efforts to eliminate mother-to-child transmission of syphilis. We examined spatial variations and clustering of syphilis prevalence among pregnant young women in Central Uganda.

We analysed secondary data from a randomised trial that evaluated the effectiveness of three antenatal syphilis partner notification approaches (NCT02262390). This study analysed clustering of syphilis prevalence by administrative division in Kampala and Wakiso districts, using Moran’s I tests and Local Indicator of Spatial Association (LISA). We used the Kulldorff Spatial-Scan Poisson model to classify divisions with high or low syphilis prevalence (HP/LP) based on 95% statistical significance. We estimated prevalence ratios for sociodemographic and bio-behavioural HIV risk factors associated with clustering, stratified by HIV status, using modified Poisson regression.

Of 422 young women diagnosed with syphilis, 26 (6%) had HIV and syphilis. The median age was 26 years (IQR 24-29). Most (314, 74%) were in monogamous marriages, and half (50%) had ≤13 years of schooling. Syphilis prevalence clustering was negatively correlated with being in a polygamous marriage (adjusted prevalence ratio [APR]=0.64; 95%: 0.47-0.88), having an unplanned pregnancy (APR=0.78; 95% CI: 0.64-0.93) and HIV testing >3 months prior (APR=0.83, 95% CI: 0.72-0.95). Syphilis prevalence was significantly higher in 3 of 12 clusters–Kasangati Town Council (Relative Risk [RR]=2.79, p<0.0001), Kawempe (RR=2.52, p<0.0001), and Nabweru (RR=1.95, p=0.0002), and lower in one cluster–Kyengera Town Council (RR=0.12, p0.05). Random patterns of syphilis prevalence were detected across all divisions (Moran’s I=0.08, p=0.19). However, some neighbouring divisions had similar prevalence: Kawempe (1.06, p=0.02) and Nabweru (0.54, p=0.045). LISA analysis confirmed high syphilis prevalence in northern divisions (Kawempe and Nabweru; p=0.01). By contrast, Central Region had neighbouring low and high prevalence divisions (Kawempe and Central; p=0.001).

Syphilis prevalence was similar within neighbouring divisions, but highest in Kasangati Town Council and Kawempe. Scaling up spatial analysis application tools enables the detection of clusters where interventions can be targeted to eliminate congenital syphilis. Competing Interest Statement The authors have declared no competing interest. Clinical Trial NCT02262390 Funding Statement Yes Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Not Applicable The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The STOP trial was approved by the Joint Clinical Research Centre Research Ethics Committee (JC1214), the Uganda National Council for Science and Technology (HS1681), and the Johns Hopkins IRB (NA_00012998/CR00015330). All study participants provided written informed consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Not Applicable I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Not Applicable I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Not Applicable Data Availability The dataset is publicly available on the repository with this DOI: https://doi.org/10.5281/zenodo.16874894.