There has been a sharp increase in the number of Australians contracting HIV, the virus that leads to AIDS.

New statistics show the number of infections across the country rose by 10 per cent last year - the fastest increase in about 20 years.

Every year the Kirby Institute at the University of New South Wales releases a report on sexually transmissible infections (STIs) in Australia.

The latest report is not a good one, with increases reported for nearly all STIs.

But the most concerning numbers relate to HIV cases, according to the Kirby Institute's Professor David Wilson, who conducted the study.

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"It's very alarming what's happening with HIV at the moment. We've had over 1,250 cases of HIV recorded, that's those that have been diagnosed," he told AM.

"There are about 25 per cent of cases that are undiagnosed in Australia as well."

The number of new HIV infections has been trending upwards in recent years. ( ABC News Online )

Professor Wilson says there is also a disturbing trend in HIV infection among Indigenous Australians, with a higher proportion of new infections from injecting drugs.

HIV: the facts 1253 new cases of HIV diagnosed in 2012

1253 new cases of HIV diagnosed in 2012 10 per cent increase in number of reported cases between 2011 and 2012

10 per cent increase in number of reported cases between 2011 and 2012 Most cases occurring in men who have unprotected sex with men

Most cases occurring in men who have unprotected sex with men New HIV diagnoses increasing since 1999

New HIV diagnoses increasing since 1999 HIV targets immune cells, weakening them and causing Acquired Immune Deficiency Syndrome (AIDS)

HIV targets immune cells, weakening them and causing Acquired Immune Deficiency Syndrome (AIDS) People with AIDS have increased risk of other infections and cancers

People with AIDS have increased risk of other infections and cancers Once regarded as death sentence, antiviral medicines allow many people to have normal life span

Once regarded as death sentence, antiviral medicines allow many people to have normal life span Many in developing countries don’t have access to these medicines

Many in developing countries don’t have access to these medicines 25,708 people in Australia living with diagnosed HIV infection at end of 2012

25,708 people in Australia living with diagnosed HIV infection at end of 2012 About 34 million people worldwide have HIV Source: ABC Health & Wellbeing

He warned of a "horrible epidemic" in the Aboriginal population if nothing is done to address the issue.

"There's no reason why we might not expect to see HIV start to rise and be really a horrible epidemic in that Aboriginal population, unless we do some active prevention and start to mitigate these rates now," he said.

'Perhaps a little bit of complacency has set in'

Professor Wilson says while good education about HIV remains, people may have just become complacent.

"HIV is no longer the death sentence it once was. With good, effective treatments, it can keep people alive to almost a full life expectancy. So I think it's perhaps a little bit of complacency that's set in," he said.

Bill Whittaker from the National Association of People with HIV says state governments are doing good work to address HIV, but the national response lags behind.

"It's a bit patchy, particularly the Commonwealth Government has been slow to respond to recent scientific advances in HIV and to get on board with the states and territories in trying to reverse these trends," he said.

Professor Wilson says greater numbers of people being tested cannot account for such a large increase in new cases.

The rise in diagnosed HIV infections in Australia shows that we are continuing to fail our young men and women, writes Robert Mitchell in The Drum.

"Unfortunately it does appear that, particularly in the gay community, condoms are not being used as much," he said.

"And we're seeing that particularly among the young men, those in their 20s, those that weren't exposed to a lot of the public health campaigns of the '80s and '90s."

The Australian Federation of AIDS Organisations says there has been a significant rise in gay men with casual partners having unprotected sex, particularly among men aged under 25.

Executive director Rob Lake says there is a need for a new strategy to encourage condom use and HIV testing.

"There's a sense that HIV is an old story and visibility of people with HIV, because we've had such good results in terms of treatments, people getting well," he said.

"HIV isn't how it was... 15 or 20 years ago."