HIV rates in Australia are at a 20-year high, with researchers saying that a complacency about unprotected sex is a leading contributor to the increase.

Annual data released by the Kirby Institute shows that 1,235 cases were diagnosed in the past year, with HIV rates steadily rising since 1999, according to an ABC report.

There are now 26,000 Australians living with the disease.

• Town to undergo tests for HIV

The research estimates that one in seven people with HIV are unaware that they have the virus, often being diagnosed with the disease after their immune systems have already been damaged.

“In some cases, people are living for several years without knowing they are HIV-positive,” Associate Professor David Wilson told the ABC.

“If people wait a long time before getting diagnosed, or if they do not start treatment once diagnosed, it is not as easy to recover.”

The figures have been released ahead of a global AIDS conference in Melbourne next week.

Researchers say they are concerned that a complacency about unprotected sex between casual male partners is a leading contributor to the increased infection rate.