Reaching the unreachable: Using targeted online advertising to promote STI screening among sex workers in Israel

Sex workers represent one of the highest-risk population for sexually transmitted infections (STIs), yet they remain underserved by conventional health systems. While STI prevalence remains relatively low in the general populations of most high-income countries, sex workers face significantly higher exposure to both viral and bacterial infections. Despite the importance of early diagnosis and treatment, structural and social barriers, including stigma, legal precarity, and lack of health insurance, limit access to preventive care and routine screening. This study evaluates the effectiveness of a keyword-based online advertising campaign aimed at increasing engagement with free and anonymous STI screening services among sex workers in Israel. The campaign targets individuals actively searching for STI-related symptoms or sexual health information, using algorithm-driven ad delivery to guide them toward testing services. We assess the campaign's effectiveness in reaching the target population and promoting actual service uptake, using metrics such as click-through rates, appointment scheduling, and confirmed clinic visits. Beyond measuring reach and appointment scheduling, the study tests which types of messaging, i.e. framing mechanisms such as appeals to present bias, social support, competitiveness, or alert, are most effective in encouraging testing behavior. We also compare two methods for linking online exposure to offline behavior: geographic conversion tracking and direct conversion via online appointment scheduling. Finally, a cost-effectiveness analysis will estimate the cost per additional STI screening generated by the campaign. The study aims to generate evidence on how digital advertising tools, particularly those driven by AI and behavioral insights, can be leveraged to improve public health access for hard-to-reach and stigmatized populations.