THURSDAY, May 12 (HealthDay News) -- People with HIV can reduce the risk of infecting their sex partners by more than 90 percent if they start treatment with antiretroviral drugs when their immune system is still relatively healthy, researchers announced Thursday.

The study, which included 1,763 mostly heterosexual couples from nine countries, was supposed to last until 2015, but the results were released early because of the significance of the findings. The research confirmed a belief held by many scientists and physicians -- that starting drug therapy early can help to limit rates of transmission of the virus that causes AIDS.

"We set out to prove that if you took earlier therapy you could benefit your own health and you could prevent the transmission of HIV," said lead researcher Dr. Myron Cohen, director of the Institute for Global Health and Infectious Diseases at the University of North Carolina at Chapel Hill.

"Both of those hypotheses were realized," he said.

The study, which started in 2005, randomly assigned the couples to two treatment groups: In the first group the HIV-infected individual began taking a combination of three antiretroviral drugs immediately. In the second group, the HIV-positive person delayed drug therapy until their CD4 T-cell count -- a blood test that measures immune system health -- either dropped below 250 or an AIDS-related illness (such as pneumocystis pneumonia) set in.

Both groups also received HIV care, which included counseling on safe sex, free condoms, treatment for sexually transmitted infections, regular HIV testing and evaluation, and treatment for any HIV-related complications.

The trial was conducted at 13 sites in nine countries including the United States, Botswana, Brazil, India, Kenya, Malawi, South Africa, Thailand and Zimbabwe.

In looking over the preliminary findings, the data and safety monitoring board shepherding the study identified 39 new cases of HIV among the previously uninfected partners. In 28 of these cases, genetic analysis confirmed that one partner had infected the other.

Of these 28 infections, 27 -- or 96 percent -- occurred among couples in which the HIV-infected partner did not start antiretroviral therapy immediately.

Cohen cautioned that the findings don't apply to all HIV-positive people. "Our couples had big advantages," he said. "We enrolled couples who probably have a low overall transmission [HIV] rate," he said.

The researchers also made sure that the patients were taking their antiretroviral medications. And, the medications were carefully selected. "The drugs are important," Cohen said. "We didn't use any combination possible -- we used ones we thought would sterilize the genital tract," he said.

Commenting on the study, Dr. Alexis Powell, an assistant professor of infectious diseases at the University of Miami Miller School of Medicine, said that "it's nice to finally have evidence-based information that clearly shows that earlier treatment with antiretrovirals can benefit the individual who is HIV-positive, but also protects sexual partners who are HIV-negative."

Most doctors would like to treat HIV patients sooner, Powell said. "We clearly understand that patients benefit with earlier treatment," she said. "And this is another reason to start early."

Powell said she'd like to put HIV patients on antiretrovirals as soon as they are diagnosed, but there are barriers. They include criteria for treatment set by insurance companies and lack of funding to treat those without insurance, she said.

"When you start talking about the dollars and cents of everyday clinical practice, that's when we are really going to see what we are going to be allowed to do," Powell said.

Another barrier is convincing some HIV-positive people to take the drugs. Some are reluctant to start taking medications that they will have to take for the rest of their lives, while others are wary of side effects. Some people think the drugs make you sicker than the virus. And still others distrust the medical system to act in their best interest, Powell said.

She cautioned that the study findings do not mean that people can stop practicing safe sex. Men, especially, need to use a condom to protect themselves or their partners, Powell said.

More information

For more on HIV/AIDS, visit AIDS.gov.