A report published by the United Nations says the number of new AIDS cases is going down around the world. But it says the AIDS epidemic is evolving and prevention programs need to be adjusted to fit the changes.

The UN's 2009 AIDS update says the number of new HIV infections has been reduced by 17 percent over the past eight years.

In East Asia the numbers have gone down by 25 percent and in Sub-Saharan Africa by 15 percent.

Karen Stanecki is senior epidemiologist at the United Nations Program on HIV/AIDS, which co-published the report with the World Health Organization.

She says although the number of new cases is going down, more people are living with HIV now than ever before.  

"The number of new infections is going down," Stanecki said. "The number of people living with HIV remains about the same because as more and more people get on treatment, people are living longer - so the number of people living with HIV may actually go up in some cases."  

She says the downturn is important, but more needs to be done. In Africa there were 400,000 new HIV infections in 2008 and many more worldwide.  

"We estimate that 2.7 million new infections occurred in 2008, so we're still seeing significant number of people becoming infected, even though it's lower than it has been in the past," Stanecki said.

According to the report, over 30 million people are living with HIV globally and 2 million people died of AIDS related illness in 2008.

Stanecki says more focus needs to be made on targeted AIDS prevention.

She says, for example, that few HIV prevention programs are in place for people over 25, those in stable relationships, and for widowers and divorcees. These groups, she says, have high HIV levels in Sub-Saharan Africa.

"In some generalized epidemics, particularly in East and Southern Africa, we see a fair number of infections occurring in people over the age of 25 who are in married and stable relationships but there are no prevention programs, or very few prevention programs, for those people," Stanecki said.

The report says funding for HIV prevention has become the smallest percentage of the HIV budgets of many countries. In Swaziland, where an estimated 25 percent of the population is HIV positive, only 17 percent of the country's budget for AIDS was spent on prevention.

Sub-Saharan Africa has the highest levels of HIV and AIDS in the world.

The region has just over 10 percent of the world's population, but is home to almost 70 percent of all people living with HIV.