In the first public health study of its kind, researchers have found that in couples in which one person is HIV-positive and the other is not, also known as serodiscordant couples, the use of antiretroviral therapy can help reduce the risk of transmission of the disease - at least in the short-term.

The study was timed to coincide with World AIDS Day.

Antiretroviral therapy has been shown to have a benefit in a clinical trial before. However, this study was the first time researchers applied the findings in a public health setting.

The study was conducted in China over the course of nine years.

In total, there were 38,862 couples studied in the trial. 24,057 couples received antiretroviral therapy, while 14,805 couples did not. The couples who did not receive the therapy did not meet the federal guidelines required to receive treatment.

In the group of treated couples, 1.3 cases were transmitted per 100 person-years. In the untreated couples, 2.6 cases were transmitted per 100 person-years. The researchers say that this means that antiretroviral therapy accounted for a 26 percent lowered risk of HIV transmission.

That finding is significantly higher than that of the clinical trial. The trial found that antiretroviral therapy lowered the risk of infection by 89 percent.

Researchers also note that the reduced transmission risk only held true for about a year. In later years, transmission rates between the treated and untreated group became about the same.

The researchers also noted that transmission rates were lowered in cases where the partner had been infected through "blood or plasma transfusion or heterosexual intercourse", but not in pairings where one partner had become infected through the use of needles.

Keith Alcorn, from NAM Aidsmap, an HIV/AIDS advocacy group, said to the BBC that the difference between this study and the clinical trial could be accounted for with a number of different explanations. He said that people could have stopped taking the drugs due to side effects, or that some people were not following the drug regime as well as those involved with the clinical trial.

The World Health Organization suggests that all HIV-positive patients in serodiscordant couples take antiretroviral therapy.

The study was published in The Lancet.

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