Real‐World Dynamic Patterns and Predictors of Antiretroviral Therapy Adherence Among Adults Living With HIV in Belgium: Evidence From Group‐Based Trajectory Modeling

ABSTRACT Purpose People living with HIV (PLWH) face many challenges in adhering to antiretroviral therapy (ART). Measuring individual changes in adherence is essential to assess quality of care and to manage healthcare costs. This study aimed to identify patterns of ART adherence among adult PLWH in Belgium over a 24‐month follow‐up period. Methods A retrospective analysis of longitudinal data related to PLWH in Belgium was conducted using the Pharmanet database from 2019 to 2022. Adherence was assessed monthly and reported as the proportion of days covered. Group‐based trajectory modeling was used to identify adherence patterns, with changes within each trajectory described using chi‐square tests. Unordered multinomial logistic regression was used to identify predictors. Results We included 15 128 prevalent ART users, 2076 of whom were incident ART users living with HIV, 65.3% were male, 40.4% were aged between 35 and 49 years, and 44.9% lived in the Flanders region. During follow‐up period, 61.0% of prevalent users and 52.1% of incident users maintained optimal adherence. Three groups (“consistently high” (61.0%), “moderately decreasing” (28.6%), and “highly decreasing” (10.4%)); and four groups adherence trajectories (“consistently high” (52.1%), “moderately decreasing” (24.3%), “early decrease” (12.9%), and “late decrease” (10.8%)) were identified respectively among prevalent and incident ART users. Female sex, younger age, living in the Brussels‐Capital Region, and treatment initiation during the COVID‐19 pandemic were significantly associated with suboptimal adherence. Conclusions ART adherence during the 24 months of follow‐up among PLWH in Belgium was suboptimal. Interventions targeting at‐risk groups during periods of declining adherence are needed among PLWH.