Primary Care Engagement Among Individuals with Experiences of Homelessness and Serious Mental Illness: an Evidence Map

Background Experiences of homelessness and serious mental illness (SMI) negatively impact health and receipt of healthcare. Interventions that promote the use of primary care services for people with both SMI and homelessness may improve health outcomes, but this literature has not been evaluated systematically. This evidence map examines the breadth of literature to describe what intervention strategies have been studied for this population, elements of primary care integration with other services used, and the level of intervention complexity to highlight gaps for future intervention research and program development. Methods We followed an a priori protocol developed in collaboration with clinical stakeholders. We systematically searched the published literature to identify interventions for adults with homelessness who also had SMI. We excluded case reports, editorials, letters, and conference abstracts. Data abstraction methods followed standard practice. Data were categorized into intervention strategies and primary care integration strategies. Then we applied the Complexity Assessment Tool for Systematic Reviews (iCAT_SR) to characterize intervention complexity. Results Twenty-two articles met our inclusion criteria evaluating 15 unique interventions to promote engagement in primary care for adults with experiences of homelessness and SMI. Study designs varied widely from randomized controlled trials and cohort studies to single-site program evaluations. Intervention strategies varied across studies but primarily targeted patients directly (e.g., health education, evidence-based interactions such as motivational interviewing) with fewer strategies employed at the clinic (e.g., employee training, multidisciplinary teams) or system levels (e.g., data sharing). We identified elements of primary care integration, including referral strategies, co-location, and interdisciplinary care planning. Interventions displayed notable complexity around the number of intervention components, interaction between intervention components, and extent to which interventions were tailored to specific patient populations. Discussion We identified and categorized elements used in various combinations to address the primary care needs of individuals with experiences of homeless and SMI.