March 3 (Bloomberg) -- HIV infections in Victoria, Australia's second-most-populous state, may climb 74 percent over the next seven years unless rising rates of unprotected sex in Melbourne are reversed, researchers said.

New HIV cases among gay and bisexual men in Queensland state may jump 20 percent by 2015, according to mathematical modeling by the University of New South Wales using surveys and disease patterns. The study, released today, forecast 12 percent fewer infections in New South Wales, where condom use has risen.

The forecast highlights the consequences of unprotected sex that has fueled a resurgence of the AIDS-causing virus in the U.S., U.K. and other developed nations during the past decade. The discovery in the mid-1990s of new antiretroviral drugs, known as protease inhibitors, has enabled people to live with HIV for years -- if not decades -- longer than they could before.

``Over time, people have become much more complacent about the risk of HIV'' and safer sex, said David Wilson, who led the study at the university's National Centre for HIV Epidemiology and Clinical Research in Sydney. ``They now perceive HIV as a manageable, lifetime chronic infection, given the improvements in HIV antiretroviral therapies,'' he said in a Feb. 29 interview.

About 11 percent of gay and bisexual men in Australia had HIV in 2006, the researchers said.

In the southeastern state of Victoria, new HIV cases reached 234 in 2006, double the number in 1999. Infections jumped by 68 percent to 122 cases in the northeastern state of Queensland during the same period, Wilson and colleagues wrote in their 102-page report.

Condom Use

Condom use declined in both states. Gay and bisexual men don't use condoms as much as 40 percent of the time in Victoria and Queensland, compared with 20 to 25 percent in 1999, Wilson said. In New South Wales state, the frequency of unprotected sex fell to 30 percent in 2006 from 40 percent in 2001, he said.

Unprotected anal sex has also led to higher rates of syphilis, gonorrhea, chlamydia and other sexually transmitted infections in gay populations, according to the study. The diseases, which can cause sores and bleeding, can lead to a twofold to fivefold increase in the risk of HIV transmission, Wilson said.

Cases of infectious syphilis in Victoria reached 420 last year from 117 in 2005. The state's Department of Human Services, which is responsible for fighting HIV there, didn't respond to a request for comment.

To contact the reporter on this story: Simeon Bennett in Sydney at sbennett9@bloomberg.net

Last Updated: March 3, 2008 06:03 EST