Canadian researchers have published a large cohort study indicating that higher uptake of antiretroviral therapy might reduce HIV transmission considerably in some populations.
While there is widespread recognition that limiting HIV replication by taking ART makes HIV-positive people less infectious, evidence is still limited regarding the population-level HIV prevention impact of expanding ART coverage.
The Canadian team set out to assess the epidemiological dynamics of treatment and prevention by conducting a province-wide analysis of trends in antiretroviral usage, viral load levels and new HIV diagnoses in British Columbia from 1996 to 2009. They found notable associations between these three variables, and also found that ART usage among injecting drug users (IDUs) greatly influenced outcomes.
In their paper in the August 14, 2010 edition of The Lancet, the researchers refined conclusions announced at a conference in early 2010. The paper reports that during two periods of expanding ART coverage in British Columbia, new HIV infections declined by 40% in the period between 1996 and 1999, and then by 23% in the period 2004-2009.
In contrast the number of new diagnoses remained stable during the period 2000-2003 when skepticism about early treatment was at its height and many patients previously taking treatment chose to interrupt treatment.
ART is available for free to all residents of British Columbia.
Researchers considered whether the observed declines in new HIV diagnoses might have resulted from fewer HIV tests being performed, but they found that testing in British Columbia actually increased during the study years. They note that when the numbers tested for HIV have increased in other studies, this has been associated with an increase in HIV diagnoses.
Researchers rejected the possibility that declines might reflect changes in sexual behavior, pointing to the fact that increasingly more cases of sexually transmitted syphilis, gonorrhea and Chlamydia had been reported from 1996 to 2008.
The paper acknowledges that while there were clear associations between ART coverage, new HIV diagnoses and viral load levels, the design of the study makes it impossible to definitively attribute these findings to cause-and-effect relationships.
Still, it notes, “Ample supportive evidence exists regarding the preventive effect of [ART] on HIV transmission, derived from vertical transmission studies and from cohort studies of serodiscordant couples, IDU cohorts and population-based studies.”
Interest in the population-level impact of “treatment as prevention” has increased in recent months, partly because of debate about the conclusions that a team of World Health Organization researchers has drawn from mathematical modeling. In a late 2008 Lancet article, they proposed that universal HIV testing and immediate treatment for all HIV-positive people in the worst-off countries could greatly slow the spread of the epidemic.
Other researchers have criticized the WHO analysis, and a UK team recently published a modeling exercise that takes different factors into account. The team concluded that the impact of treating more HIV-positive people would vary in accordance with HIV risk behavior in different settings.
Association of highly active antiretroviral therapy coverage, population viral load, and yearly new HIV diagnoses in British Columbia, Canada: a population-based study.
Julio SG MontanerViviane D LimaRolando BarriosBenita YipEvan WoodThomas KerrKate ShannonP Richard HarriganRobert S HoggPatricia DalyPerry Kendall
Lancet 376: 532 – 539, 2010. doi:10.1016/S0140-6736(10)60936-1
Link to The Lancet abstract