The rate of annual new HIV infections in the US is about 40 per cent higher than previously thought, and African American men and women suffer nearly half of all new infections, US public health officials said Saturday.

The re-calculation showed that in 2006, an estimated 56,300 new HIV infections occurred, much higher than the previous estimate of 40,000 new annual infections.

The report, published in a special HIV/AIDS issue of the Journal of the American Medical Association (JAMA) on the eve of the international AIDS conference in Mexico City from Sunday to Friday, said the figures resulted from new technology and methodology developed by the Centers for Disease Control (CDC) in Atlanta, Georgia.

The CDC, which released a summary of the journal article, said the figures did not represent an increase in the actual number of HIV infections, and that the incidence of HIV had been stable at that higher level since the late 1990s.

Contracting the HIV virus usually leads to the fatal disease, Acquired Immune Deficiency Syndrome (AIDS), which is spread through sexual relations, infected blood transfusions and drug needles. It was first identified in the mid 1980s. More than a quarter of a century into the AIDS epidemic, 25 million people have died and an estimated 33.2 million people are living with HIV/AIDS.

In contrast to changes in the US methodology, international AIDS officials have actually lowered the overall world estimate of those infected over the past year, using a refined methodology for counting.

The CDC said the new US estimates show the most affected US groups are gay and bisexual men of all races and ethnicities, representing about 53 per cent of all new infections, and African American men and women, who comprise 13 per cent of the US population but 45 per cent of new HIV infections in 2006.

The report warned that HIV incidence ahs been increasing among gay and bisexual men, confirming suspicion of increased risky behaviour.