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The number of people with HIV

JOHN Donnelly's June 20 front-page news story, "Estimates on HIV called too high," raises important issues about the difficulties of estimating the number of people living with HIV worldwide. The article correctly points out that AIDS remains the most dangerous pandemic in the developing world. However, while we acknowledge that previously published estimates were slightly higher than our newly revised figures (to be released on July 6), the specialists cited in the article are incorrect in claiming that global HIV estimates have been inflated by 25 to 50 percent.

The UNAIDS 2004 Report on the global AIDS epidemic features revised HIV prevalence rates for previous years, allowing for a better understanding of the epidemic's trends. Estimates are constantly being improved on the basis of new data and research findings.

While the article refers to this as errors in statistical models, we believe these are improvements that continue to provide us with a more accurate picture of the AIDS epidemic.

Comparing the latest estimates with those published in previous years will lead to misleading conclusions, as seen in the Donnelly article. The latest estimates cannot be compared directly with previously published estimates. Why not? Because the assumptions, methodologies, and data used to produce the estimates are constantly being improved thanks to greater knowledge of the epidemic and better surveys from countries around the globe.

For the first time, the report compares new estimates for 2003 with revised estimates for 2001 based on improved methodologies. There is no gold standard for HIV surveillance. HIV estimates, whether they are based on household surveys or surveys of pregnant women, need to be assessed critically as the epidemic evolves. Achieving 100 percent certainty about the numbers of people living with HIV globally, for example, would require repeatedly testing every person in the world for HIV, which is logistically impossible.

Donnelly's article might lead readers to think that AIDS is not as pervasive as once thought. This couldn't be further from the truth. The actual number of people living with HIV globally continues to grow at alarming rates due to new HIV infections.

Manager, Epidemic and
Impact Monitoring
Geneva, Switzerland

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