Sir

We would like to provide our perspective on your Book Review of two books criticizing the Joint United Nations Programme on AIDS (UNAIDS), 'Time for a change?' (Nature 447, 531–532; 2007), and the coverage of this issue at http://www.nature.com/news/2007/070528/full/070528-6.html.

In his book The AIDS Pandemic: The Collision of Epidemiology with Political Correctness, James Chin accuses UNAIDS of exaggerating data for the sake of advocacy, which is not true. Nor are UNAIDS data influenced by political or fundraising agendas. The UNAIDS Secretariat and the World Health Organization work closely with other technical partner organizations to assist countries in better understanding their HIV epidemics so they can respond appropriately. Estimations are produced in close collaboration with national epidemiologists and governments, using methodologies recommended by an international team of experts chaired by a leading academic from Imperial College London.

UNAIDS is committed to providing the most accurate information available and continues to be transparent in publicizing the methods used to assess the magnitude of the past and current epidemics. UNAIDS has always stated that countries should use the most comprehensive and most recent data available. Reassessments of earlier published estimates of prevalence, incidence and mortality have been made, and we expect that there may be adjustments in the future.

Helen Epstein's The Invisible Cure also makes inaccurate statements about the work of UNAIDS: in particular, we have always advocated the reduction of number of sexual partners as an effective strategy for HIV prevention, as can be seen from our reports and other contributions to the published record. All UNAIDS documents on the prevention of sexual transmission of HIV advocate abstinence, reduction of sexual partners and correct use of male and/or female condoms. (See, for example, http://data.unaids.org/Global-Reports/Bangkok-2004/UNAIDS_Bangkok_press /GAR2004_pdf/GAR2004_ExecSumm_en.pdf)

UNAIDS and its partners will continue their mission to gather the best-quality data to assist in shaping an effective global response to AIDS.