Everyone with HIV infection should receive immediate, not deferred, treatment, say researchers after significant interim trial results.

The risk of death or serious illness was halved in HIV-positive people who received immediate treatment, according to a trial with global implications.

The trial's interim results were so clear-cut that the international study, co-ordinated by the Kirby Institute at UNSW, has been terminated ahead of schedule.

Receiving immediate antiretroviral therapy (ART) was proved to be clinically superior to a generally recommended approach.

This involves deferring treatment until CD4 cells, the key immune cells targeted by HIV, dropped, from the healthy range of above 500, to 350 cells or less per microlitre of blood.

The recommended threshold should be scrapped and everyone with HIV infection should be treated, the Institute's Professor Sean Emery told a media briefing.

The Strategic Timing of AntiRetriviral Treatment (START) study involved 4685 HIV-positive people, from 35 countries, whose CD4 count was above 500 cells.

They were randomly allocated to receive treatment immediately or when their CD4 count dropped to around 350 cells and, on average, were followed up over three years.

Overall 127 people died or became ill with Aids or other serious illnesses such as cancer or liver disease, with 41 of those having received immediate treatment and 86 deferred treatment.

"These findings have global implications for the treatment of people living with HIV," Prof Emery said.

"As a result of this trial, we now know that treatment at all stages of disease extends survival and prevents serious disease complications in people with HIV infection."

Previous studies have shown a reduced risk of HIV transmission among people on ART.