Interventions to improve sexual health among the homeless community: a realist review protocol

Introduction

Homelessness is a complex and dynamic condition that manifests in multiple forms. It is frequently classified into unsheltered homelessness (e.g., sleeping rough or in vehicles), sheltered homelessness (e.g., use of emergency accommodation), and hidden homelessness (e.g., temporary stays with friends or family, often unrecorded in official statistics). The European Typology of Homelessness and Housing Exclusion (ETHOS) offers a nuanced conceptual framework detailing the full spectrum of the experience of homelessness, encompassing rooflessness, houselessness, insecure housing, and inadequate housing¹. This typology is particularly relevant for research adopting a realist approach, as it supports an examination of how varying housing circumstances shape vulnerability and access to support. Across jurisdictions, definitions of homelessness vary based on policy, legal, and service delivery frameworks. In the U.S., homelessness is narrowly defined by the Department of Housing and Urban Development (HUD) based on the absence of a fixed, adequate nighttime residence². In contrast, Canada and Ireland adopt broader definitions. Ireland’s Housing Act of 1988, for instance, includes those whose accommodation is unsuitable or poses a risk to health and safety³. These definitional differences reflect deeper structural and cultural assumptions about the causes and consequences of homelessness and inform how states respond.

As of early 2025, homelessness in Ireland has reached unprecedented levels, with 14,864 people recorded in emergency accommodation—the highest since national records began⁴. Homelessness is underpinned by poverty, housing precarity, and systemic exclusion, and is associated with considerable disparities in physical and mental health^5,6. Sexual health is a particularly neglected domain. The World Health Organization (WHO) defines sexual health as a state of physical, emotional, mental, and social well-being in relation to sexuality. It is not merely the absence of disease or dysfunction but requires a positive and respectful approach to sexuality and sexual relationships, as well as the possibility of having pleasurable and safe sexual experiences, free from coercion, discrimination, and violence⁷.

Sexual health encompasses a wide range of issues, including access to contraception, prevention, and treatment of sexually transmitted infections (STIs), sexual education, and the ability to engage in consensual, safe sexual activities. For the people experiencing homelessness, maintaining sexual health is particularly challenging due to the instability and risks associated with their living situations. Research indicates that people experiencing homelessness are more likely than their housed counterparts to engage in high-risk sexual behaviours, such as having unprotected sex, engaging in transactional sex, or having multiple sexual partners^8,9. These behaviours, combined with limited access to sexual health services, stigma, and the transient nature of homelessness contribute to elevated rates of STIs and other sexual health issues within this community^10,11.

Existing reviews of sexual health interventions targeting people experiencing homelessness and other high-risk populations highlight promising strategies but suffer from several shared limitations in scope and methodology. Wright and Walker conducted a narrative systematic review of sexual health interventions among homeless people who use drugs¹². While they identified potentially effective behavioural and attitude change interventions, their findings were constrained by a limited six included studies, and a lack of exploration into how circumstantial and structural factors influenced outcomes and is now outdated. A systematic review by Naranbhai et al. focused specifically on HIV prevention among young people experiencing homelessness¹³. The authors were only able to include three RCTs for their review. They concluded that the lack of quality evidence and the heterogeneity in intervention characteristics hindered the synthesis of evidence regarding the effectiveness of these interventions. Brown et al. reviewed behavioural and psychosocial interventions for youth in high-risk communities¹⁴. Like Naranbhai et al.’s review, the authors only included three studies in their review with regards to the homeless community without being able to come to conclusions as to how these interventions might work or whether they are effective as the studies were too heterogeneous to synthesise.

Notably, the aforementioned reviews were mostly restricted to trials, either intentionally or unintentionally as most non-trial studies did not meet the quality criteria to be included, which limit their ability to account for the complexity of homelessness and healthcare interventions as well as their broader circumstances. Prioritising trials also risks leaving out broader implementation studies or qualitative evaluations that could provide richer insight into how interventions function the real world. Together, these reviews suggest that while there is emerging evidence of what works, the reliance on trials—though methodologically rigorous—often excludes valuable insights from mixed-methods, qualitative, or naturalistic studies. Such exclusions are particularly problematic in the homelessness field, where lack of funding, instability, and ethical concerns make controlled trials challenging. This highlights a pressing need for a different method for evidence synthesis that includes a broader evidence base and which is specifically designed to understand complex interventions and circumstances.

Protocol

This realist review seeks to explore how and why sexual health interventions for people experiencing homelessness lead to different outcomes, depending on individual circumstances and broader social circumstances. This protocol is registered on PROSPERO (CRD420251047807).

Methods

The current review will be conducted following a structured, theory-driven process composed of six iterative steps according to Pawson’s guidelines¹⁶. These include: (i) identifying the review question, (ii) searching for primary studies, (iii) quality appraisal, (iv) extracting the data, (v) synthesizing the data and (vi) disseminating the findings.

First, the scope of the review is clarified by defining the research question in realist terms—focusing on what works, for whom, in what circumstances, and how—and by developing an initial programme theory to guide inquiry. Second, a systematic search for evidence is conducted across diverse sources, including both academic and grey literature, to identify data relevant to understanding how interventions function. Third, the evidence is appraised and extracted based on the relevance to the research question and the rigour of the study which produced it. Fourth, evidence is synthesised through the development and refinement of CMOCs, and then ultimately producing theories that explain how mechanisms are triggered under different contextual conditions to produce outcomes. Iterative data searching can take place at any point during the steps 2–4. Fifth, the programme theory is continually refined and tested throughout the review process as needed. Finally, the findings are disseminated in ways that are useful to policymakers, practitioners, and other stakeholders, emphasising transferable insights about how interventions operate.

Dissemination

Results will be shared via peer-reviewed journal publications and conference presentations in the fields of public health, homelessness, and sexual health. In alignment with our commitment to patient and public involvement, accessible summaries will also be co-developed with public and patient involvement (PPI) contributors to share findings in plain language through community organisations, outreach networks, and advocacy groups. Key insights—particularly refined CMOCs—will be presented in visual formats such as logic models or evidence maps to support policy and practice uptake without the use of research jargon. Additionally, findings will be shared with stakeholders in health and homelessness services to inform future intervention design, delivery, and commissioning.

Conclusion

This realist review protocol outlines a comprehensive plan to investigate how sexual health interventions function for people experiencing homelessness, for whom, and under what circumstances. Moving beyond traditional systematic reviews which are designed to synthesise trial-based outcomes and effect sizes, this approach will synthesise evidence from a diverse range of study designs. By developing and testing CMOCs, the review aims to build theories that are transferable across settings. This theory-driven synthesis will help uncover the underlying mechanisms that shape intervention success or failure, while accounting for key contextual factors such as housing status and access to care. Meaningful patient and public involvement (PPI) will guide the review to ensure its relevance and impact. Ultimately, this work will inform more equitable, effective, and sustainable approaches to sexual health for the homeless community.

Review stage

The review has completed the IPT development stage, where the IPT was brought in for discussion with the expert advisory group to gather their insights and feedback. The next phase of the review will involve an in-depth literature review and realist data synthesis, aimed at testing and further refining the programme theories.

Ethical considerations

There are no ethical considerations necessary as this is a review study synthesising published literature. No primary data will be collected.