Purpose: Examine incidence and factors associated with loss to follow-up (LTFU) in the AIDS Clinical Trials Group (ACTG) Longitudinal Linked Randomized Trials (ALLRT) cohort.
Method: ALLRT is a prospective cohort of HIV-infected persons randomized to antiretroviral (ARV) regimens/strategies in ACTG trials and followed long-term after the trial ends. Person-years were calculated from ALLRT entry until loss to follow-up (LTFU; defined using off-study reasons or ≥ 3 consecutive missed visits), death/ severe debilitation/site closures, or June 2009 (censored). Poisson regression was used to examine LTFU factors separately among participants who were ARV naïve or ARV experienced at trial entry.
Results: Among 4,630 participants (22,524 person-years), 1,140 were lost to follow-up, 237 died, 29 were severely debilitated, and 443 were at sites that closed. The LTFU incidence was 5.5 and 4.2 per 100 person-years among previously ARV-naïve and ARV-experienced participants, respectively. In both groups, age ≤ 50, site location, being off ARVs, and viral load ≥ 400 copies/mL were associated with a higher risk of LTFU. Among ARV-naïve participants, male sex, education <16 years, intravenous drug use, and cigarette smoking were also associated with LTFU.
Conclusion: Knowledge of differential LTFU can help researchers identify participants at risk of LTFU in longitudinal HIV cohorts and design retention strategies, thereby limiting study bias. The identified factors should be included in inverse probability of weighting models to account for LTFU.