The Impact of Behavioural Economics-Informed Interventions on the Care Cascade for Sexually Transmitted and Blood-Borne Infections: A Systematic Review of Randomized Controlled Trials

Introduction: While behavioural economics principles are widely used for public health interventions, a comprehensive understanding of their impact across the sexually transmitted and blood-borne infections (STBBIs) care cascade remains limited. We systematically evaluated the effectiveness of behavioural economics-informed interventions for an STBBI care cascade. Methods: We systematically searched five major literature databases from their inception to 25 April 2024, with the search updated on 22 March 2025. We included randomized controlled trials (RCTs) evaluating behavioural economics-informed interventions, that is strategies such as incentives, defaults, framing and reminders designed to influence health-related decision-making, at any stage of the care cascade for STBBIs. The cascade included three domains: prevention, care engagement and treatment adherence. Two reviewers independently extracted data and assessed the risk of bias using the Cochrane RoB-2 tool. Due to significant heterogeneity, findings were synthesized narratively using a three-stage care cascade framework. Results: Our search identified 2546 records, of which 40 RCTs met the inclusion criteria and evaluated 12 distinct behavioural economics-informed intervention types. Incentives were the most common intervention, including monetary, lottery and voucher-based incentives (25/40; 63%). Monetary and voucher incentives effectively improved outcomes across multiple cascade stages, including prevention (such as safer sex, male medical circumcision), care engagement (testing for HIV, HBV and HCV) and treatment adherence (such as retention in care, viral suppression). Opt-out defaults showed strong, sustained effects on HIV/HCV screening. Pay-it-forward strategies significantly increased dual STBBI testing and often demonstrated cost-effectiveness. A substantial proportion of studies (27/40; 67.5%) reported a high risk of bias. Discussion: Behavioural economics-informed interventions showed stage-specific effects across the STBBI care cascade. Monetary incentives were the most consistently effective, especially for prevention, testing and some adherence outcomes. Defaults and pay-it-forward were promising for screening uptake, whereas crowdsourcing appeared more useful for intervention design. Overall, effectiveness depended on intervention design and context. Conclusions: Behavioural economics-informed interventions hold substantial promise for optimizing the STBBI care cascade, but no single strategy was universally optimal. Future research should strengthen the evidence base and assess the transferability of these interventions across diseases and context-specific settings to inform wider implementation and maximize global public health impact.