ArticlesAssociation of highly active antiretroviral therapy coverage, population viral load, and yearly new HIV diagnoses in British Columbia, Canada: a population-based study
Introduction
Despite recent progress, neither a cure nor a preventive vaccine against HIV-1 infection is likely to become available in the near future. Several preventive strategies have not been wholly effective for several reasons, including insufficient support, logistical difficulties, poor implementation, and underuse.1 As a result, the global effect of HIV/AIDS continues to grow. In 2008, an estimated 33·4 million people were living with HIV, there were 2·0 million AIDS-related deaths,1 and an alarming 2·7 million new HIV infections occurred. These developments have prompted the UN Joint Programme on HIV/AIDS to call for an urgent redoubling of efforts in the fight against HIV/AIDS.2
HIV treatment has advanced remarkably since 1996, with the development and refinement of highly active antiretroviral therapy (HAART). HAART stops HIV replication on a sustained basis and, as a result, plasma HIV-1 RNA concentrations (henceforth viral load) typically become undetectable. This change allows for immune reconstitution to take place, leading to long-term disease remission and aversion of the otherwise fatal course.3, 4 By 2006, at least 3 million years of life had been saved in the USA as a direct result of HAART within a decade.5 In high-income countries, life expectancy of HIV-positive individuals aged 20 years who were taking HAART was roughly two-thirds of that of the general population.6
Interest has increased in the possible secondary effect of HAART—reduction of HIV transmission.7, 8, 9, 10, 11, 12, 13 The association between high plasma HIV-1 RNA concentration and high risk of HIV transmission has long been understood.14, 15 In addition to decreasing plasma viral load to undetectable levels, HAART decreases viral load in other biological fluids, including semen and vaginal secretions.16, 17 Although exceptions have been reported,18, 19, 20, 21 from a public health perspective the association between viral load and other bodily fluids is quite strong, especially in the setting of long-term, sustained, and effective HAART.22 Strong proof of principle regarding the effect of HAART on HIV transmission has been shown in studies of vertical transmission in resource-rich and resource-poor settings.23
New evidence suggests that HAART can decrease HIV transmission in other settings. Reductions in rates of HIV transmission of more than 90% have been reported in several cohort studies of heterosexual HIV-serodiscordant couples in whom the index partner was treated with HAART.24, 25 Similarly, reduction in community viral load as a result of HAART was shown to be a key determinant of decreasing HIV incidence in a cohort of injecting drug users (IDUs) in Vancouver, Canada.26 Investigators have also documented this effect in retrospective population-based observational studies in Taiwan,27 the province of British Columbia, Canada,10 and the city of San Francisco, USA.28 However, the estimated effect of increased HAART coverage on HIV transmission varies greatly between mathematical models, with results ranging from elimination10, 13 to potential worsening29 of the HIV epidemic. We therefore undertook this study with the aim of analysing at a population level the potential association between expansion of HAART coverage, viral load, and new HIV diagnoses per year in a Canadian province with free access to HIV care.
Section snippets
Study design and participants
We used two separate unlinked databases in this population-based cohort study. Data for number of HIV tests done and new HIV diagnoses in the province of British Columbia, Canada, between 1996 and 2009, were obtained from the British Columbia Centre for Disease Control (BCCDC).30 BCCDC is the single provincial agency that centralises all HIV surveillance data for the province and has access to HIV testing data from the provincial public health reference laboratory, which does more than 90% of
Results
Between 1996 and 2009, the number of individuals actively receiving HAART in British Columbia increased from 837 to 5413 (547%; p=0·002), and the number new HIV diagnoses fell from 702 to 338 cases per year (−52%; p=0·001). The overall correlation between number of individuals on HAART and number of new HIV diagnoses per year was −0·89 (p<0·0001).
HAART usage and new yearly HIV diagnoses showed three distinct phases during the study (figure 1). Between 1996 and 1999, we retrospectively noted a
Discussion
Our results show a strong and significant association between increased HAART coverage, reduced community viral load, and decreased number of new HIV diagnoses per year in the population of a Canadian province. We had a unique opportunity to characterise the evolution of these variables during a 15-year period within a universal health-care environment with centralised and free access to HAART. During our study, the pattern of use of HAART changed strikingly on the basis of contemporary
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