Improved monitoring of the pandemic has led the United Nations to revise its estimates, particularly in Southern Africa and Asia, resulting in a major revision in the assessment of India's epidemic, the country previously thought to be worst-hit.
"South Africa is the country with the largest number of HIV infections in the world," read the UNAIDS annual report on the epidemic for 2007.
While the report did not give a figure, the South African government currently estimates some 5.5 million of the country's 48 million population are living with the disease.
While AIDS continued to be the leading cause of death in Africa, sub-Saharan Africa was the worst affected region.
"More than two out of three (68 percent) adults and nearly 90 percent of children infected with HIV live in this region, and more than three in four (76 percent) AIDS deaths in 2007 occurred there, illustrating the unmet need for antiretroviral treatment in Africa."
Women in the region bear the brunt of the disease.
"Unlike other regions, the majority of people (61 percent) living with HIV in sub-Saharan Africa are women," the report found.
"It is estimated that 1.7 million people were newly infected with HIV in 2007, bringing to 22.5 million the total number of people living with the virus" that causes AIDS.
Southern Africa was the worst affected in the region with national adult HIV prevalence over 15 percent in eight countries.
"While there is evidence of a significant decline in the national HIV prevalence in Zimbabwe, the epidemics in most of the rest of the subregion have either reached or are approaching a plateau."
The UN data showed that adult HIV prevalence was either stable or has started to decline in many parts of Africa.
According to the report, Kenya and Zimbabwe were some of the countries where the slowing trend of new infections was most evident, with similar shifts in Burkino Faso, Ivory Coast and Mali.
Worldwide, new infections of AIDS were levelling off, and of the 2.5 million people newly infected overall, more than half come from sub-Saharan Africa.