In a finding that could dramatically change the lives of HIV-positive people and public health policies in Australia, a study of 282 gay men on treatment with undetectable levels of the virus in their blood found that none transmitted it to their partners through unprotected sex over one year.

A previous 2010 study of mainly heterosexual couples showed that having an undetectable viral load reduced by 96 per cent the risk of transmitting the virus to an HIV-negative partner.

HIV experts said although the latest data presented from the PARTNER study at a US conference this week suggested an ''extremely low and possibly zero risk'', it was too early to tell people they should abandon condoms.

However, they said the study boosted hopes that a strategy of ''treatment as prevention'' could play a major role in stemming the spread of HIV and should prompt the Commonwealth government to explore more home-based testing so people know their status and can be treated earlier.

Professor Andrew Grulich, of the Kirby Institute, said that while some Australian states including NSW and Victoria had already introduced more rapid HIV testing to encourage people to know their HIV status, Australia should follow the US and allow tests to be sold over the counter in pharmacies.

''I think home-based testing absolutely has a place … because treatment as prevention critically depends on people with HIV being diagnosed as early as possible, so they know they are infected and can take action to reduce their infectivity before they have any unsafe sex with anybody,'' he said.

Head of infectious diseases at The Alfred hospital in Melbourne, Professor Sharon Lewin, said a ''treatment as prevention'' strategy was promising because about 90 per cent of people on antiretroviral treatment had undetectable levels of the virus in their blood when they had tests, usually at six-monthly intervals.

But she said limiting the spread of the virus was complex because at the moment about 8000 of the 33,000 people with HIV in Australia did not know they were infected.

''It's thought that about 50 per cent of new infections come from people who don't know they are infected,'' said Professor Lewin, a world-leading HIV researcher.

Furthermore, she said only about half of the 25,000 people who knew they were HIV positive were receiving antiretroviral treatment for a range of reasons, including a historical requirement for people to show a certain amount of immune system damage to receive subsidised treatment. However, Professor Lewin said a recent change by the federal government meant Australian doctors could now prescribe treatment without restrictions, a move that might lead to more people being treated earlier after diagnosis.

President of the National Association of People Living with HIV Australia, Robert Mitchell, said: ''These results provide further evidence of the powerful impact that HIV treatment has on preventing HIV transmission. It is important that every effort is made to alert people with HIV and their doctors to these latest findings, particularly as this study is the first of its kind to include a significant number of gay couples.''