Impact of Substance Use and Mood/Anxiety Disorders on the HIV Continuum of Care in British Columbia, Canada, from 2001 to 2019

People living with HIV (PLWH) are disproportionately affected by mood, anxiety, and substance use disorders that prevent their sustained engagement with HIV care. Comprehensive research on the impact of these disorders on the HIV continuum of care is lacking. This study aimed to assess the impact of the syndemic between substance use disorder (SUD) and mood/anxiety disorders on the HIV continuum of care for PLWH in British Columbia (BC), Canada, and identify the stage with the highest attrition in the continuum. This retrospective population-based cohort study utilized data from the Comparative Outcomes And Service Utilization Trends (COAST) study that contains data on all diagnosed PLWH in BC. Eligible individuals were ≥ 19 years of age and were followed during 2001–2019. Our exposure variable was SUD or mood/anxiety disorder diagnoses. Our outcomes were the achievement of the following stages of the HIV continuum of care: (1) antiretroviral therapy (ART) initiation, (2) on-ART, (3) ART adherence, (4) viral suppression, and (5) maintained suppression. We estimated attrition by estimating the proportion of PLWH who proceed to each stage. Generalized linear mixed-effect models assessed the association between SUD and mood/anxiety disorders and the achievement of each stage while controlling for sociodemographic and HIV-related confounders. For the 14,398 eligible PLWH, maintained suppression exhibited the highest attrition. Having SUD or both SUD and mood/anxiety disorder were significantly associated with reduced odds of achieving all stages of the HIV continuum of care except on-ART. SUD had the strongest association with reduced odds of ART adherence (adjusted odds ratio (aOR) 0.47; 95