Incidence of HIV Type 1 Drug Resistance Detection.

Improved Virological Outcomes in British Columbia Concomitant with Decreasing Incidence of HIV Type 1 Drug Resistance Detection.

There have been limited studies evaluating temporal changes in the incidence of detection of drug resistance among human immunodeficiency virus type 1 (HIV-1) isolates and concomitant changes in plasma HIV load for treated individuals in a population-wide setting. Longitudinal plasma viral load and genotypic resistance data were obtained from patients receiving antiretroviral therapy from the British Columbia Drug Treatment Program from July 1996 through December 2008. A total of 24,652 resistance tests were available from 5422 individuals. The incidence of successful plasma viral load suppression and of resistance to each of 3 antiretroviral categories (nucleoside/nucleotide reversetranscriptase inhibitors, nonnucleoside reverse transcriptase inhibitors, and protease inhibitors) was calculated for the population receiving therapy. There has been a drastic decrease in the incidence of new cases of HIV-1 drug resistance in individuals followed during 1996–2008. In 1997, the incidence rate of any newly detected resistance was 1.73 cases per 100 person-months of therapy, and by 2008, the incidence rate had decreased 112-fold, to 0.13 cases per 100 person-months of therapy. This decrease in the incidence of resistance has occurred at an exponential rate, with halftimes on the order of 2–3 years. Concomitantly, the proportion of individuals with plasma viral load suppression has increased linearly over time (from 64.7% with HIV RNA levels !50 copies/mL in 2000 to 87.0% in 2008; R2p0.97; P ! .001). The authors’ results suggest an increasing effectiveness of antiretroviral therapy at the populational level. The vast majority of treated patients in British Columbia now have either suppressed plasma viral load or drug-susceptible HIV-1, according to their most recent test results.

Rather than investigating the prevalence of transmitted drug resistance in the population or the prevalence of acquired drug resistance among people on treatment, these investigators, who were uniquely placed to do so, assessed the incidence of drug resistance over a 12-year period. They found exponential decreases in the incidence rate of drug resistance, including NNRTI (non-nucleoside reverse transcriptase inhibitor) resistance (40-fold decrease), despite increases in annual and cumulative exposure to antiretroviral drugs. These authors conclude that efforts to improve accessibility to antiretroviral treatment have the potential to greatly reduce HIV-1 levels in a population without increasing the risk of drug resistance.