Objectives: To analyse the incidence, prevalence, and predictors for development of triple-class antiretroviral drug failure (TCF) in individuals infected with HIV.
Design: Population-based observational cohort study from 1 January 1995 to 31 December 2003, focusing on all 2722 recipients of highly active antiretroviral therapy (HAART) in Denmark.
Methods: We used person-years analysis, Kaplan-Meier survival curves and Cox regression analysis. TCF was defined as a minimum of 120 days with viral load > 1000 copies/ml on treatment with each of the three major drug classes.
Results: We observed 177 TCFs, yielding a crude incidence rate (IR) of 1.8 per 100 person-years [95% confidence interval (CI), 1.6-2.1]. Seven years after initiation of HAART, 17.2% (95% CI, 14.5-20.5) of antiretroviral (ART)-experienced patients, but only 7.0% (95% CI, 4.3-11.2) of ART-naive patients were estimated to have failed. After an initial rise, the IR from the third to the sixth year of HAART declined significantly for ART-experienced patients [incidence rate ratio (IRR), 0.80 per year (95% CI, 0.66-0.97); P = 0.022], and non-significantly for ART-naive patients [IRR, 0.79 per year (95% CI, 0.53-1.18); P = 0.255]. The IR for all patients being followed each year declined from 1997 to 2003 [IRR, 0.88 (95% CI, 0.81-0.96); P = 0.002]. The prevalence of TCF remained stable at less than 7% after 2000. Predictors of TCF at commencement of HAART were a CD4 cell count below 200, a previous AIDS-defining event, previous antiretroviral exposure, earlier year of HAART initiation, and young age.
Conclusions: The risk of TCF is declining in Denmark and the prevalence remains stable.