Effective ART dramatically reduces the risk of HIV transmission, and mathematical models have suggested that universal voluntary testing and widespread treatment could essentially halt the spread of the epidemic. Two studies presented at CROI offered early indications that expanded testing and treatment may be helping to lower HIV incidence in "real-world" settings in high-income, low-prevalence countries.
Moupali Das-Douglas from the San Francisco Department of Public Health (abstract 33) reported that between 2004 and 2008, a 40% decrease in "community viral load" -- or viral load across an entire population group -- was associated with a 50% reduction in new HIV diagnoses (including both recent infections and new diagnoses of existing infections).
By 2008, an estimated 80% of newly diagnosed individuals were linked to care; about 90% of these were on ART, and about 75% of treated people achieved undetectable viral load. The investigators concluded that these findings "support the hypothesis that wide-scale early ART can have a preventive effect at a population level."
Julio Montaner and colleagues from the British Columbia Centre for Excellence in HIV/AIDS (abstract 88LB), a group that has pioneered mathematical modeling of the effects of treatment, explored associations between expanded HIV testing, ART coverage, community viral load, and decreased HIV transmission in British Columbia, largely driven by injection drug users (IDUs) in the Downtown Eastside district of Vancouver.
The number of HIV tests performed annually in British Columbia rose from 153,635 in 2004 to 182,151 in 2008, and the number of people receiving ART doubled from about 2,500 in 2000 to about 5,000 in 2009. Average community viral load declined over the past five years, and the proportion of people with HIV RNA levels below 500 copies/mL increased from about 40% in 2004 to about 75% in 2009. During the same period, total new HIV diagnoses decreased, including a steep decline among IDUs (from 150 cases in 2004 to 80 in 2009).
The researchers said these findings "demonstrate an association between expanded [ART] coverage, decreased provincial plasma viral load, and decreased new HIV diagnoses," which followed initiation of a treatment outreach effort targeting IDUs. Montaner suggested the decrease was likely due to expanded ART rather than behavior change, since needle exchange and other harm reduction efforts were widely implemented well before the decline began.
While the correlations observed in these studies do not prove causation, the findings suggest that increased testing, more widespread treatment, and reduced community viral load can provide community-wide benefits by lowering the risk of HIV infection.
Liz Highleyman (firstname.lastname@example.org) is a freelance medical writer based in San Francisco.