Sex Transm Infect 88:i11-i16 doi:10.1136/sextrans-2012-050640
  • Supplement

Updates to the Spectrum/Estimation and Projection Package (EPP) model to estimate HIV trends for adults and children

Open Access
  1. Milly Marston3
  1. 1Futures Institute, Glastonbury, Connecticut, USA
  2. 2Research Program, East-West Center, Honolulu, Hawaii, USA
  3. 3Department of Population Studies, London School of Hygiene and Tropical Medicine, London, UK
  1. Correspondence to John Stover, Futures Institute, 41A New London Turnpike, Glastonbury, Connecticut 6033, USA; JStover{at}
  1. UNAIDS Report 2012 Guest Editors

  2. Karen Stanecki

  3. Peter D Ghys

  4. Geoff P Garnett

  5. Catherine Mercer

  • Accepted 26 July 2012


Background The Spectrum and Estimation and Projection Package (EPP) programs are used to estimate key HIV indicators based on HIV surveillance and surveys, programme statistics and epidemic patterns. These indicators include the number of people living with HIV, new infections, AIDS deaths, AIDS orphans, the number of adults and children needing treatment, the need for preventing mother to child transmission (PMTCT) and the impact of antiretroviral treatment on survival.

Methods The Joint United Nations Programme on HIV and AIDS (UNAIDS) Reference Group on Estimates, Models and Projections regularly reviews new data and information needs and recommends updates to the methodology and assumptions used in Spectrum. The latest updates described here were used in the 2011 round of global estimates.

Results Spectrum and EPP have now been combined into one software package to enhance ease of use and ensure consistent data and assumptions for the curve fitting and indicator estimations. Major enhancements to the methods include a new adult model that tracks the HIV+ population by CD4 count; new patterns describing child survival by time of infection (perinatally, <6 months, 7–12 months and 12+ months after birth); a more detailed estimate of mother-to-child transmission that includes differential transmission rates by CD4 count of the mother, the effects of incident infections and new prophylaxis options; and new procedures to estimate uncertainty ranges around regional estimates.

Conclusions The revised model and software facilitate the preparation of new HIV estimates and use new data to address emerging needs for better information on need for treatment among adults and children.


  • Contributors JS, TB and MM all contributed to the writing and review of the paper. JS led the development of the Spectrum software. TB led the development of the EPP software. MM conducted the child survival analysis.

  • Funding Funding for this work was provided by UNAIDS and the Bill and Melinda Gates Foundation.

  • Competing interests None.

  • Provenance and peer review Commissioned; externally peer reviewed.

  • Open Access This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: and