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This paper reviews the data sources and methods used to estimate the number of people on, and coverage of, antiretroviral therapy (ART) programmes in low- and middle-income countries and to monitor the progress towards the '3 by 5' target set by WHO and UNAIDS. We include a review of the data sources used to estimate the coverage of ART programmes as well as the efforts made to avoid double counting and over-reporting. The methods used to estimate the number of people in need of ART are described and expanded with estimates of treatment needs for children, both for ART and for cotrimoxazole prophylaxis. An estimated 6.5 million people were in need of treatment in low- and middle-income countries by the end of 2004, including 660 000 children under age 15 years. The mid-2005 estimate of 970 000 people receiving ART in low- and middle-income countries (with an uncertainty range. 840 000-1 100 000) corresponds to a coverage of 15% of people in need of treatment. Copyright © 2006 World Health Organization [ABSTRACT FROM AUTHOR]

Objectives: In the Declaration of Commitment of the 2001 United Nations General Assembly Special Session on AIDS, all Member States agreed to a series of actions to address HIV. This article examines the availability of data to measure progress toward reducing HIV incidence and AIDS mortality and discusses the extent to which changes can be attributed to programs., Methods: Lacking a method to directly measure HIV incidence, trends in HIV prevalence among 15-year to 24-year olds and groups with high-risk behaviors are used as a proxy measure for incidence trends among adults in generalized and concentrated/low-level epidemics, respectively. Although there is limited empirical data on trends in new infections among children, progress in the treatment area is tracked through indicators for the percentage of people who remain on antiretroviral treatment 12 months after initiation and the coverage of antiretroviral treatment. Successive iterations of epidemiological models using surveillance data from pregnant women and groups with high-risk behavior and data from national household surveys, demographic data and epidemiological assumptions have produced increasingly robust estimates of HIV prevalence, incidence and mortality., Results: Globally, incidence has decreased among adults (accompanied by evidence of changes in behavior in several countries) and children over the past decade. The decline in AIDS mortality is more recent. On the basis of the underlying logical framework and mathematical models, it is concluded that programs have contributed to a reduction in HIV incidence and AIDS mortality., Conclusions: More data are needed to reliably inform trends in HIV incidence and AIDS mortality in many countries to allow an assessment of progress against national and global targets. In addition, impact evaluation studies are needed to assess the relationship between changes in incidence and mortality and the HIV response and to determine the extent to which these changes can be attributed to specific programmatic interventions.

Objectives: To investigate epidemiological patterns and trends of HIV infection and sexual behaviour among young people aged 15-24 years in the nine countries in southern Africa most affected by the HIV epidemic., Methods: Data on HIV prevalence among young people in the general population were obtained from national population-based surveys conducted between 2000 and 2007, whereas data on sexual behaviour were obtained from repeat surveys between 1994 and 2007. Linear or exponential regression was used to analyse HIV prevalence trends among young women attending antenatal clinics in recent years., Results: Patterns of HIV infection among young people are similar across the countries included in this analysis. The prevalence of HIV increases after the age of 15 years, more rapidly among women than among men, reaching a peak among women in their twenties and men in their thirties. Between 2000 and 2007 the prevalence of HIV among antenatal clinic attendees was constant in Mozambique and South Africa and declining in Lesotho, Namibia, Swaziland, Zambia, Botswana, Malawi and Zimbabwe, but only reached statistical significance (P < 0.05) in the last three. Changes towards safer sexual behaviour were observed over time among young men and women in the general population in this region., Conclusion: Sexual behaviour changes among young people are encouraging and are associated with declines in HIV prevalence among young antenatal clinic attendees over time. More research is needed to understand the recent changes and the very high prevalence among young women in this region. Interventions aimed at reducing risky behaviour need to be supported and expanded while incorporating new approaches to prevention.

Background: Since 1998 the Joint United Nations Programme on HIV/AIDS and the World Health Organization has provided estimates on the magnitude of the HIV epidemic for individual countries. Starting with the 2003 estimates, plausibility bounds about the estimates were also reported. The bounds are intended to serve as a guide as to what reasonable or plausible ranges are for the uncertainty in HIV incidence, prevalence, and mortality., Methods: Plausibility bounds were developed for three situations: for countries with generalised epidemics, for countries with low level or concentrated epidemics (LLC), and for regions. The techniques used build on those developed for the previous reporting round. However the current bounds are based on the available surveillance and survey data from each individual country rather than on data from a few prototypical countries., Results: The uncertainty around the HIV estimates depends on the quality of the surveillance system in the country. Countries with population based HIV seroprevalence surveys have the tightest plausibility bounds (average relative range about the adult HIV prevalence (ARR) of -18% to +19%.) Generalised epidemic countries without a survey have the next tightest ranges (average ARR of -46% to +59%). Those LLC countries which have conducted multiple surveys over time for HIV among the populations most at risk have the bounds similar to those in generalised epidemic countries (ARR -40% to +67%). As the number and quality of the studies in LLC countries goes down, the plausibility bounds increase (ARR of -38% to +102% for countries with medium quality data and ARR of -53% to +183% for countries with poor quality data). The plausibility bounds for regions directly reflect the bounds for the countries in those regions., Conclusions: Although scientific, the plausibility bounds do not represent and should not be interpreted as formal statistical confidence intervals. However in order to make the bounds as meaningful as possible the authors have tried to apply reasonable statistical approaches and assumptions to their derivation. An understanding of the uncertainty in the HIV estimates may help policy makers take better informed decisions to address the epidemic in their respective countries.

Identification of causes of changes in prevalence and incidence of HIV at a national level is important for planning future prevention and intervention needs. However, the slow progression to disease and the sensitive and stigmatising nature of the associated behaviours can make this difficult. Changing rates of incidence are to be expected as an epidemic progresses, but separating background changes from those brought about by changes in behaviour and interventions requires careful analysis. This paper discusses the criteria required to determine whether observed changes in HIV prevalence are the result of changes in behaviour.

A strong, global commitment to expanded prevention programs targeted at sexual transmission and transmission among injecting drug users, started now, could avert 28 million new HIV infections between 2005 and 2015. This figure is more than half of the new infections that might otherwise occur during that period in 125 low- and middle-income countries. Although preventing these new infections would require investing about U.S.$122 billion over this period, it would reduce future needs for treatment and care. Our analysis suggests that it will cost about U.S.$3900 to prevent each new infection, but that this will produce a savings of U.S.$4700 in forgone treatment and care costs. Thus, greater spending on prevention now would not only prevent more than half the new infections that would occur from 2005 to 2015 but would actually produce a net financial saving as future costs for treatment and care are averted.

Background: Through major efforts to reduce costs and expand access to antiretroviral therapy worldwide, widespread delivery of effective treatment to people living with HIV/AIDS is now conceivable even in severely resource-constrained settings. However, the potential epidemiologic impact of treatment in the context of a broader strategy for HIV/AIDS control has not yet been examined. In this paper, we quantify the opportunities and potential risks of large-scale treatment roll-out., Methods and Findings: We used an epidemiologic model of HIV/AIDS, calibrated to sub-Saharan Africa, to investigate a range of possible positive and negative health outcomes under alternative scenarios that reflect varying implementation of prevention and treatment. In baseline projections, reflecting "business as usual," the numbers of new infections and AIDS deaths are expected to continue rising. In two scenarios representing treatment-centered strategies, with different assumptions about the impact of treatment on transmissibility and behavior, the change in the total number of new infections through 2020 ranges from a 10% increase to a 6% reduction, while the number of AIDS deaths through 2020 declines by 9% to 13%. A prevention-centered strategy provides greater reductions in incidence (36%) and mortality reductions similar to those of the treatment-centered scenarios by 2020, but more modest mortality benefits over the next 5 to 10 years. If treatment enhances prevention in a combined response, the expected benefits are substantial-29 million averted infections (55%) and 10 million averted deaths (27%) through the year 2020. However, if a narrow focus on treatment scale-up leads to reduced effectiveness of prevention efforts, the benefits of a combined response are considerably smaller-9 million averted infections (17%) and 6 million averted deaths (16%). Combining treatment with effective prevention efforts could reduce the resource needs for treatment dramatically in the long term. In the various scenarios the numbers of people being treated in 2020 ranges from 9.2 million in a treatment-only scenario with mixed effects, to 4.2 million in a combined response scenario with positive treatment-prevention synergies., Conclusions: These analyses demonstrate the importance of integrating expanded care activities with prevention activities if there are to be long-term reductions in the number of new HIV infections and significant declines in AIDS mortality. Treatment can enable more effective prevention, and prevention makes treatment affordable. Sustained progress in the global fight against HIV/AIDS will be attained only through a comprehensive response.

Objectives: To establish the accuracy of the country specific estimates of HIV prevalence, incidence, and AIDS mortality published every 2 years by UNAIDS and WHO., Methods: We review sources of error in the data used to generate national HIV/AIDS and where possible estimate their statistical properties. We use numerical and approximate analytic methods to estimate the combined impact of these errors on HIV/AIDS estimates. Heuristic rules are then derived to produce plausible bounds about these estimates for countries with different types of epidemic and different qualities of surveillance system., Results: Although 95% confidence intervals (CIs) can be estimated for some sources of error, the sizes of other sources of error must be based on expert judgment. We therefore produce plausible bounds about HIV/AIDS estimates rather than statistical CIs. The magnitude of these bounds depends on the stage of the epidemic and the quality and coverage of the sentinel HIV surveillance system. The bounds for adult estimates are narrower than those for children, and those for prevalence are narrower than those for new infections., Conclusions: This paper presents a first attempt at a rigorous description of the errors associated with estimation of global statistics of an infectious disease. The proposed methods work well in countries with generalised epidemics (>1% adult HIV prevalence) where the quality of surveillance is good. Although methods have also been derived for countries with low level or concentrated epidemics, more data on the biases in the estimation process are required.

This paper describes the Estimation and Projection Package (EPP) for estimating and projecting HIV prevalence levels in countries with generalised epidemics. The paper gives an overall summary of the software and interface. It describes the process of defining and modelling a national epidemic in terms of locally relevant sub-epidemics and the four epidemiological parameters used to fit a curve to produce the prevalence trends in the epidemic. It also provides an example of using the EPP in a country with a generalised epidemic. The paper discusses the strengths and weaknesses of the software and its envisaged future developments.

Background: The Joint United Nations Programme on HIV and AIDS (UNAIDS) and the World Health Organization (WHO) have produced country-specific estimates of HIV/AIDS biannually since 1997. These estimates are a primary source of information about the extent and spread of the HIV/AIDS epidemic and its impact. The importance of having comparable country-specific estimates of HIV/AIDS is growing as estimates are used to determine how international resources to fight HIV/AIDS will be allocated to countries., Objectives: This paper describes the procedures and process used to make the 2001 round of UNAIDS/WHO estimates of HIV/AIDS. The paper focuses on the different approaches used to make estimates of prevalence in countries with generalized and low-level and concentrated epidemics as well as on new curve-fitting software that was developed to produce epidemic curves for each country. In addition, it presents the assumptions used (e.g. survival from infection to death, the rate of mother-to-child transmission) that are required to derive estimates of incidence and mortality in adults, as well as prevalence, incidence and mortality in children., Conclusion: The paper describes the general process by which the estimation and modelling procedures have been refined and improved over time. The paper also discusses the limitations and weaknesses of the procedures and the data used to make the estimates, and suggests areas where further improvements need to be made.

HIV/AIDS has reached pandemic proportions, and is one of the leading causes of death worldwide. In 2001, the Declaration of Commitment on HIV/AIDS set out several aims with respect to reducing the effect and spread of HIV/AIDS, and an expanded response in low-income and middle-income countries was initiated. Here we examine the potential effect of the expanded global response based on analyses of epidemiological data, of mathematical models of HIV-1 transmission, and a review of the impact of prevention interventions on risk behaviours. Analyses suggest that if the successes achieved in some countries in prevention of transmission can be expanded to a global scale by 2005, about 29 million new infections could be prevented by 2010.

Objective: The objective of this paper was to analyse the quality of HIV/AIDS sentinel surveillance systems in countries and the resulting quality of the data used to make estimates of HIV/AIDS prevalence and mortality., Methods: Available data on sero-surveillance of HIV/AIDS in countries were compiled in the process of making the end of 1999 estimates of HIV/AIDS. These data came primarily from the HIV/AIDS Surveillance Database developed by the United States Census Bureau, from a database maintained by the European Centre for the Epidemiological Monitoring of AIDS and all country reports on sentinel surveillance that had been provided to World Health Organization or UNAIDS. Procedures were developed to score quality of surveillance systems based on four dimensions of quality: timeliness and frequency; appropriateness of groups; consistency of sites over time; and coverage provided by the system. In total, the surveillance systems from 167 countries were analysed., Results: Forty-seven of the 167 countries whose surveillance systems were rated were judged to have fully implemented sentinel surveillance systems; 51 were judged to have systems that had some or most aspects of a good HIV surveillance system in place and 69 were rated as having poorly functioning or non-existent surveillance systems., Conclusion: This analysis suggests that the quality of HIV surveillance varies considerably. The majority of countries most affected by HIV/AIDS have systems that are providing sufficient sero-prevalence data for tracking the epidemic and making reasonable estimates of HIV prevalence. However, many countries have poor systems and strengthening these is an urgent priority.

Objective: This paper presents the methods used to calculate the end of 1997 country-specific estimates of HIV and AIDS produced by the UNAIDS/WHO Working Group on Global HIV/AIDS and STD Surveillance. The objective of this exercise was to improve estimates on HIV/AIDS by using country-specific models of HIV/AIDS epidemics. The paper describes and discusses the processes and obstacles that were encountered in this multi-partner collaboration including national and international experts., Methods: The 1997 estimates required two basic steps. First, point prevalence estimates for 1994 and 1997 were carried out and the starting year of the epidemic was determined for each country. The procedures used to calculate the estimates of prevalence differed according to the assumed type of the epidemic and the available data. The second step involved using these estimates of prevalence over time and the starting date of the epidemic to determine the epidemic curve that best described the spread of HIV in each particular country. A simple epidemiological program (EPIMODEL) was used for the calculation of estimates on incidence and mortality from this epidemic curve., Results: Regional models that were used in previous estimation exercises were not able to capture the diversity of HIV epidemics between countries and regions. The result of this first country-specific estimation process yielded higher estimates of HIV infection than previously thought likely, with over 30 million people estimated to be living with HIV/AIDS. The application of survival times that are specific to countries and regions also resulted in higher estimates of mortality, which more accurately describe the impact of the epidemics. At the end of 1997, it was estimated that 11.7 million people worldwide had died as a result of HIV/AIDS since the beginning of the epidemic., Conclusion: This exercise is an important step in improving understanding of the spread of HIV in different parts of the world. There are, however, shortcomings in the current systems of monitoring the epidemic. Improvements in HIV surveillance systems are needed in many parts of the world. In addition, further research is needed to understand fully the effects of the fertility reduction as a result of HIV, differing sex ratios in HIV infection and other factors influencing the course and measurement of the epidemic.