Treatment as Prevention: Making Sense of the Swiss

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Several years ago, the Swiss National AIDS Commission released a statement declaring that HIV-positive individuals successfully managing their viral load (on long-term antiretroviral therapy that keeps the virus at levels below the detection limit of standard tests) sexually noninfectious. While such a bold statement was an unusual public health message—after decades of prevention efforts aimed at increasing condom use, telling some people they no longer need them seems counterproductive—one positive effect of the so-called Swiss Statement was increased interest in finding out whether treatment really can prevent infection.

The idea that reducing the amount of virus in an infected person would reduce the chance they would transmit it to a partner made sense, but until recently it hadn’t been proven in a clinical trial. An HIV Prevention Trials Network study released last month looked at 1,763 serodiscordant couples (in which one partner has HIV and the other is uninfected) in thirteen sites around the world. They gave antiretroviral drugs to all HIV-positive partners, but some began treatment earlier than usual. Half of the infected partners were given the drugs when their CD4+ T-cell count had dropped below 250 cells/mm3 (the depletion of these critical immune cells is the hallmark of AIDS) or if they developed an AIDS-related illness, which was the standard time to begin treatment according to World Health Organization guidelines at the time the study began. The other half began treatment immediately. The study found that starting treatment early reduced the chances the virus would be transmitted to the uninfected partner by a remarkable 96%. The results were so clear that the study was halted, its findings were announced four years ahead of schedule, and all HIV-positive participants in the trial were offered immediate treatment.

Thinking back to the Swiss Statement, counseling anyone against condom use could be a public health nightmare. For example, asymptomatic sexually transmitted infections can increase HIV transmission (STIs can increase viral load in genital secretions but not in blood, so an asymptomatic infection may go unnoticed), or if a person develops resistance to their antiretroviral regimen this drug-resistant virus could be passed on before it’s noted clinically. (Here are some more things to consider about the Swiss Statement). While the Swiss Statement might have been overly optimistic in ignoring real-world situations such as imperfect adherence to treatment, it did help spur on the idea that treatment can also be prevention.

Turning this idea into reality, however, will require a lot of planning and, of course, money. While the goal has always been universal access to antiretroviral drugs for all those who need it, the potential impact this treatment could have on preventing new infections has thrust the idea of treatment as prevention to the forefront of priorities in controlling the AIDS epidemic. (Here are some details on the results from the clinical trial).

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