AIDS: overestimated growth?

AIDS is a leading global cause of mortality, and remains the primary cause of death in sub-Saharan Africa. But the HIV epidemic is not growing as quickly as earlier predicted.

According to the latest report from the Joint UN Programme on HIV/AIDS and the World Health Organization, the percentage of the world's adult population carrying HIV -- a statistic known as HIV prevalence -- is leveling off, and is declining in sub-Saharan Africa.

The UN now says that 33 million people are infected with HIV, a significant downward revision to last year's estimate of nearly 40 million. It also says that 2.5 million will be infected with the virus this year, a 40% drop from the 2006 estimate.

This good news is more a story of statistical correction rather than a testament to the efficacy of existing prevention strategies. The overall number of people in the world living with HIV continues to increase, mainly because the world's population is growing. And even if an epidemic has leveled off, it can mask a situation in which the rate of AIDS-related deaths exceeds the rate of new HIV infections. This is happening in a number of countries in sub-Saharan Africa. As the LA Times notes, "we might be breaking even statistically, but we're not making progress".

Better information

Nevertheless, UNAIDS and the WHO now benefit from improved methodology, better surveillance and changes in key epidemiological assumptions, which have allowed them to present a more detailed and accurate picture of the global AIDS epidemic.

• Previous estimates of HIV prevalence extrapolated numbers for rural populations based on the number of urban dwellers seeking medical help, but this year numbers were based on door-to-door surveys in 30 heavily afflicted countries.
• Data from antenatal clinics is now used differently to help calculate HIV prevalence in the general population.
• The average number of years that people living with HIV are estimated to survive without treatment has been increased from 9 to 11 years.

Focus still on prevention

Projected financial needs for AIDS treatment will therefore be somewhat lower this year, and may be further reduced in coming years. Future resource requirements will depend not only on adjustments in estimates of the number of people needing antiretroviral treatment, but technical issues such as optimal choices of first and second-line therapy and recommendations about when to start therapy.

This may leave the focus on making existing prevention methods effective. The use of condoms, female empowerment and behavioural change -- though a difficult social challenge -- will remain among the most important HIV prevention measures.