Last week at the International AIDS Society conference, researchers presented amazing new evidence proving the efficacy of treatment as prevention. The study, HPTN 052, showed a 96 percent reduction in sexual transmission of HIV between serodiscordant couples when the infected partner initiated antiretroviral therapy (ART) early. Conference delegates were overjoyed; years of research had finally paid off with a new prevention method. But they were also cognizant of the challenges that remain in extending this benefit to the people that need it.
Current World Health Organization guidelines recommend starting ART when a patient’s CD4 count drops below 350. In the treatment arm of HPTN 052, patients with a CD4 count of between 350 and 550 started ART immediately, while in the control arm they started when their CD4 count dropped below the limit indicated by national guidelines. More details about the study results can be found here and here.
For treatment as prevention to be effective at a population level, widespread testing to identify people living with HIV is needed. Despite scale up in HIV testing over the last decade, the majority of people living with HIV are unaware of their status. In sub-Saharan Africa, 80 percent of people with HIV do not know they are infected. This is a significant barrier to implementing treatment as prevention, and one that must be addressed to realize the prevention benefit of ART.
HPTN 052 clearly shows the prevention benefits of early treatment initiation, but in order to start treatment early, people must be diagnosed early. In low-resource settings, people are often diagnosed with low CD4 counts, after the disease has progressed and they have become ill with AIDS or opportunistic infections. In order to diagnose HIV earlier, education campaigns should emphasize the importance of testing for healthy individuals.
Not only should testing be done early, it should be done as soon after infection as possible. A recent study in Malawi estimated that 38 percent of sexually-transmitted HIV infections occurred in couples where the infected partner had recently acquired the virus. Though the contribution of early infection to HIV transmission differs between settings, it is clear that acute stage transmission must be addressed to reduce new infections. This is a challenge for treatment as prevention, as individuals are rarely diagnosed during the acute phase of HIV infection. New strategies are needed to target testing toward individuals who may have been recently infected and to immediately link them to appropriate programs. Current guidelines do not recommend ART for people with acute HIV infection, but this could change given recent evidence.
In order to continue to identify HIV infections early, testing frequency will have to be increased. One model suggests that annual testing is needed to fully realize the benefits of treatment as prevention. To detect all acute infections, at risk individuals would have to be tested up to four times per year. New diagnostic tools that more accurately detect new infections are also needed.
There are promising models of provider-initiated, community-based and home-based HIV testing. Even self-testing has been shown to be acceptable and valid in a study setting. Experts at the conference agreed that a mix of testing strategies will be needed to reach different groups and that the best combination will vary according to local circumstances. Destigmatization of testing and increased community demand are important components to increasing coverage. The common theme voiced by all was the need for more resources to expand and improve HIV testing programs.
To learn more about treatment as prevention, read the Global Health Council’s factsheet, “Treatment as prevention: challenges and opportunities.”
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Granich RM, Gilks CF, Dye, C De Cock KM, Williams BG. Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model. The Lancet. 2009; 373: 48-57.
Padian NS, McCoy SI, Karim SSA, Hasen N, Kim J, Bartos M, Katabira E, Bertozzi SM, et al. HIV prevention transformed: the new prevention research agenda. The Lancet. 2011; 378: 269-278.
Powers KA, Ghani AC, Miller WC, Hoffman IF, Pettifor AE, Kamanga G, Martinson FEA, Cohen MS. The role of acute and early HIV infection in the spread of HIV and implications for transmission prevention strategies in Lilongwe, Malawi: a modeling study. The Lancet. 2011; 378: 256-268.