Risk of Viral Failure Declines With Duration of Suppression on Highly Active Antiretroviral Therapy Irrespective of Adherence Level

Objective: To model the effect of adherence and duration of viral suppression on the risk of viral rebound. Methods: Viral rebound was defined as the first of at least two consecutive viral loads greater than 400 copies/mL after initial viral suppression. The main exposures were adherence, presence of antiretroviral class resistance before rebound or censoring date, and the percentage of follow-up time with viral suppression. Results: A total of 274 (N = 1305 [21%]) individuals experienced viral rebound. Median time of suppression before rebound was 2 years. Viral rebound was less likely to occur among those with longer duration of continuous viral suppression (odds ratio, 0.37; 95% confidence interval, 0.32 to 0.42). Among individuals with moderate levels of adherence (80% to less than 95%), the probability of virologic failure was 0.85 after being suppressed for 12 months and it was 0.08 after 72 months being suppressed (P < 0.01). Individuals with drug resistance were at a higher risk of viral rebound. Conclusions: The risk of viral rebound decreased with longer duration of viral suppression within each of adherence strata studied. Although perfect adherence remains an important goal of therapy to prevent disease progression, individuals with long-term viral suppression may be able to miss more doses without experiencing viral rebound.