On the face of things, a fall in the number of people infected with HIV (the virus that causes AIDS) from 39.5m to 33.2m over the course of a single year, as reported in this year's AIDS epidemic update from the World Health Organisation (WHO) and UNAIDS, should be cause for rejoicing. Indeed, it is, for it means there are fewer people to treat, and fewer to pass the infection on, than was previously thought. But the fall is not a real fall. Rather, it is due to a change in the way the size of the epidemic is estimated.
If you factor in that change, the number of infected individuals has actually risen since last year, by 500,000. Yet even that is not necessarily bad news in the paradoxical world of AIDS. As treatment programmes are rolled out around the world, death rates are falling. According to the revised figures, the lethal peak, of 2.2m a year, was in 2005. Now the figure is 2.1m. Since the only way for an infected person to drop out of the statistics in reality (as opposed to by sleight of statistical hand) is for him to die, such increased survivorship inevitably pushes up the total size of the epidemic.
The best news of all, however, is that the new figures confirm what had previously been suspected—that the epidemic has peaked. The highest annual number of new infections around the world was 3.4m in 1998. That figure has now fallen to 2.5m.
Both the change in the death rate and the change in the infection rate are partly a consequence of the natural flow and ebb of any epidemic infection. But they are also a reflection of the hard graft of public-health workers in many countries, who have persuaded millions of people to modify or abandon risky behaviour, such as having unprotected sex, as they have also created the medical infrastructure needed to distribute anti-retroviral drugs that can keep symptoms at bay in those who do become infected.
The revision of the figures is mainly a result of better data-collection methods, particularly in India (which accounts for half the downward revision) and five African countries (which account for another fifth). In India many more sampling points have been established, and in all countries better survey methods, relying on surveyors knocking on doors rather than asking questions at clinics, have gathered data from more representative samples.
Sceptics will feel vindicated by the revision. They have suspected for a while that the older survey methods were biased, and that the inflation thus produced was tolerated because it helped twang the heart-strings of potential donors. However, the structures for collecting and distributing money to combat AIDS are now well established, and accurate data are crucial if that money is not to be misdirected. The new information also means that the goal of treatment for all who need it will be easier and cheaper to achieve. The WHO and UNAIDS are planning to publish a report on the matter early next year, but Paul De Lay, UNAIDS's director of evidence, monitoring and policy, says that the financial requirements for 2010 will probably be about 5% less than previously estimated, and that by 2015 that figure will have risen to 10%. Good news for everyone, then, donors and sufferers alike.
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