Definitions of antiretroviral treatment failure for measuring quality outcomes

Our aim was to compare three different definitions of treatment failure and discuss their use as quality outcome measures for a clinical service.

Data for treatment-naïve patients who attended the Melbourne Sexual Health Centre (MSHC) between 1 January 2000 and 31 December 2008 were analysed. Definition 1 was the strict Food and Drug Administration (FDA) definition of treatment failure as determined using the time to loss of virological response (TLOVR) algorithm. Definition 2 defined treatment failure as occurring in those whose viral load never fell to <400 HIV-1 RNA copies/mL or who developed two consecutive viral loads > or =400 copies/mL on any treatment (switching or stopping treatment with a viral load <400 copies/mL was permitted). Definition 3 was the same as definition 2 except that individuals were also deemed to have failed if they stopped treatment for 6 months or longer.

There were 310 antiretroviral-naïve patients who started treatment in the study period. Of these, 156 [50.3%; 95% confidence interval (CI) 42.1-53.3%] experienced treatment failure under definition 1, 10 (3.2%; 95% CI 1.5-5.8%) experienced treatment failure under definition 2, and 16 (4.5%; 95% CI 2.5-7.4%) experienced treatment failure under definition 3 over the 108 months of follow-up. The probability of failing definition 1 was statistically different from the probability of failing definition 2 or 3 (P=0.01).

There were significant differences in treatment failure for the three definitions. If definition 1 were used, the outcomes would be sufficiently common to enable clinics to be compared but would be less meaningful. If definition 2 or 3 were used, the events would be too rare to enable clinics to be compared, but it would be possible to set a benchmark level of success that clinics could aim to reach.