Conditional cash transfer interventions to support syphilis treatment in vulnerable populations: a quasi-experimental study among displaced and host communities in a border city of Colombia.

Background: Syphilis incidence is increasing globally; however, cost and time are significant barriers to treatment completion rates among vulnerable populations, including displaced populations and host communities. To inform public health strategies, we aimed to test whether conditional cash transfers (CCT) increased completion of syphilis treatment among a community sample in a border city of Colombia. Methods: We embedded a quasi-experimental trial of a CCT intervention in a community sexual health program serving participants aged 14 years and older in low-income settlements around Cúcuta, Colombia in 2023. The program included workshops and syphilis screening. Individuals with laboratory-confirmed syphilis were eligible for inclusion in the trial. Both control and CCT arms provided syphilis diagnostics, counseling and free treatment. CCT consisted of cash payments of USD$12.69 for completion of each of two follow-up treatments. We used generalized linear models to estimate the effect of CCT on treatment completion, defined as three doses of penicillin. Findings: Of 1751 workshop participants, 114 had laboratory-confirmed syphilis and were enrolled in the trial. Participants were 56% female (64/114) and 44% male (50/114), with 6 participants (5.3%) identifying as transgender, regardless of sex at birth. Participants included 47% Venezuelan migrants staying in Cúcuta (53/114), 26% Colombian returnees (30/114), and 19% Colombians from the host community (22/114). Data on ethnicity was not collected. Median age was 34.5 years (IQR: 25.0-46.0). More than three-quarters (78%, 39/50) of CCT participants completed the three-dose treatment regimen compared to 45% (29/64) of control participants, a risk difference of 33% (p < 0.001). In adjusted models, CCT-assigned participants had a 36% higher treatment completion rate compared to control-assigned participants (adjusted risk difference: aRD: 0.36, 95% CI: 0.19-0.53). Interpretation: Conditional cash transfers might enhance syphilis treatment adherence among populations facing socioeconomic challenges. Funding: German Development Cooperation Agency, Deutsche Gesellschaft für Internationale Zusammenarbeit.