Sexual transmission of HIV is more likely if the HIV-positive partner has a higher viral load. Because antiretrovirals therapy (ART) slows AIDS progression and reduces viral load in infected individuals, the drugs not only improve the health and prolong the life of those who take them, but also make it less likely that they infect others. As a consequence, ART has been discussed not only as a treatment but also as a prevention tool in its own right.
To test this, Baggaley and colleagues used a model to predict and compare the impacts of alternative strategies of increasing ART access in resource-poor countries. Some of the strategies included the provision of diagnostic laboratories that could routinely measure CD4 counts and viral loads of HIV-infected individuals (only if this is done could people be treated before they develop overt symptoms). They also took into account different ways that people might change their sexual behavior if they get treatment (which might make them feel physically better and more likely to be sexually active) and counseling (which will hopefully increase safe sex practices).
They found that providing ART to all individuals with AIDS symptoms (i.e. those at the late stages of the disease) was likely to increase the prevalence of HIV infection, as these people live longer and become sexually active again. If ART is also provided to HIV-positive individuals at an earlier stage, i.e. when their immune system starts to get weaker but before they develop the symptoms of AIDS, the outcome on HIV prevalence depends critically on the behavior of these individuals.
These results suggest that provision of ART to symptomatic AIDS patients and/or those at the earlier stages of the disease is not likely to prevent many new infections. It could even increase transmission of the virus as patients live longer and are healthier. Counseling patients and the rest of society to promote safe sex practices must therefore be an essential part of any strategy if it is to contain and reverse the AIDS epidemic. The model presented here can support health policy makers in resource-poor settings in their difficult task of allocating limited amounts of antiretroviral drugs for the best outcome for their populations.