Low Levels of HIV Reduce Transmission

People infected with HIV, the virus that causes AIDS, are much less likely to pass their infection on to a sex partner if they carry a low number of viral particles in their blood. The observation, reported in the 30 March New England Journal of Medicine (NEJM), suggests that virus-fighting drugs that lower so-called "viral load" might slow the epidemic. The study has raised ethical questions, however, in part because the participants did not receive antiretroviral treatment.

A drug cocktail available, for about $200 a month, in the developed world has extended the lives of many people infected with HIV. The mix of protease inhibitors and other antiviral compounds depresses the level of HIV virus in the bloodstream and seems to allow the immune system to bounce back. As a result, the rate of AIDS-related deaths has plummeted in the past few years. But no one has known to what extent viral load affects HIV transmission.

As part of a larger study on sexually transmitted diseases, researchers in Uganda examined the records of 415 long-term couples. At the beginning of the study, one partner was infected with HIV and the other was not. When epidemiologist Thomas Quinn of Johns Hopkins University and colleagues looked at blood samples taken later in the study, they found that 90 of the HIV-negative partners had been infected during the 5-year study period. They considered a number of factors that might have contributed to the transmission, such as the presence of other diseases, education, whether the male was circumcised, and viral load. The only significant factors were viral load and male circumcision. None of the 50 circumcised males whose partners were HIV-positive contracted the virus during the study. And no infected partner with a viral load less than 1500 virus copies per milliliter of blood passed the virus on.

The result "certainly suggests that HIV-positive people may be less infective when they are treated with antiretroviral drugs" shown to lower viral load, Quinn says. However, NEJM editor Marcia Angell questions the ethics of the study in an accompanying editorial, as the study participants did not receive antiviral treatment for HIV that is standard care in wealthy countries. Indeed, Angell notes, "the results will probably find their greatest application in the developed world," rather than in Uganda, as the drug cocktail that is so effective in lowering viral load is too expensive for most patients in the developing world--where most HIV-positive people live.

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