How To Make Sure You're Making The Right Precaution Decision In Terms Of HIV/AIDS
Effectively controlling the HIV epidemic will require efficient use of limited resources. Despite ambitious global goals for HIV prevention and treatment scale up, few comprehensive practical tools exist to inform such decisions. We briefly summarize modeling approaches for resource allocation for epidemic control, and discuss the practical limitations of these models. We describe typical challenges of HIV resource allocation in practice and some of the tools used by decision makers. We identify the characteristics needed in a model that can effectively support planners in decision making about HIV prevention and treatment scale up.
Section 1: HIV Epidemiology
(Deltoid Note: The Centers for Disease Control and Prevention, Toxicity Review Section, have published their own methods for modeling the risk to the community of using drug injection equipment.)
The HIV epidemic in the United States began in 1981. While most HIV outbreaks are geographically limited to specific areas, the HIV epidemic in the United States began with sexual contact in New York City in 1981. By 1985, people in all of the contiguous United States had contracted the virus, and in many communities transmission became local and intense.
For many decades before the AIDS epidemic began in the United States, the HIV epidemic had been treated as a disease of gay men and drug users. In the mid-1970s, in response to pressure from the gay community, the U.S.
The HIV Prevention and Treatment Scale Up
Beginning in the 1990s, treatment and prevention initiatives focused on individuals living with HIV and their partners. These preventive interventions led to a significant decrease in HIV transmission. Since 2004, HIV treatment has been a priority for both national and international health agencies, with new treatment drugs for patients who do not respond to first line treatments. However, despite an expansion of treatment, people living with HIV still often do not have access to effective treatment, limiting their ability to have a long, healthy life. The world's population with HIV continues to grow, and the epidemic is still not under control.
HIV modeling is a general approach to quantitative assessment of health services. Modeling helps decision makers understand resource needs and allocation, and this understanding can guide planning and delivery. Modeling helps with resource allocation, budgeting, and planning in health systems; the principles of model design are summarized in Table 1.
Focusing on an HIV outbreak or outbreak management, the key is to estimate resources needed to control or stop the outbreak. Such estimates help planners plan for and conduct interventions efficiently, with the aim of controlling or stopping the outbreak.
What is a model?
A mathematical model is a simulation or computer program that illustrates behavior of some aspect of a complex system in a way that can be directly interpreted by a decision maker. Although the model may need to be complex, complex decisions require complex models. Decision makers develop mathematical models to describe behavior of phenomena with which they are unfamiliar, which is a very different purpose than an engineer developing a model for the design of a bridge, machine, or building.
For example, a bridge needs a simple design for accuracy and safety, so a mathematical model can be used by engineers to help design bridges.
How do models work?
In order to develop a model, resources needed to eliminate an epidemic are first estimated and the number of people in each country who need to be treated is divided by the country's national life expectancy. This can be done as an exponential or logistic model. The estimates of global life expectancy over the next 10 years are based on statistics and population projections.
Using this figure, the number of people needed to be treated with antiretroviral therapy (ART) can be determined. This is the number of people needed to achieve "eradication" of the epidemic in each country.
With rapid HIV transmission and increasing treatment levels, the United Nations estimates that AIDS will be a non‐disaster by 2015. This forecast suggests that global leaders should focus on minimizing the costs of treatment and on reducing the number of new HIV infections. In particular, it recommends that 90 percent of HIV-positive people receive antiretroviral therapy. If HIV treatment can be delivered at a cost per person of US$300,000 per year, this scale‐up will also reduce societal costs by US$300 billion per year. However, achieving this goal will depend on resource allocation; specific conditions will also need to be met.
Practical Challenges in HIV Decision Making
Coordinating global health efforts. Currently there is little coherence between different health actors (e.g., health agencies, governments, NGOs) involved in HIV response. Examples include the relative hierarchy of care between health ministries and the current resource-allocation regime for HIV/AIDS management in low- and middle-income countries. Health ministries tend to prioritize policy measures and programs in relation to other policies and programs. Resource allocation between subnational government agencies is another challenge.
Developing HIV/AIDS indicators and indicators of performance. For monitoring the health impact and providing evidence of HIV/AIDS interventions to planning and decision makers, longitudinal data are essential.
Choosing the right time horizon for decision making
The low number of HIV infections in wealthy countries means that the benefits of delaying HIV diagnosis and treatment (both of which improve long-term health outcomes) outweigh the potential costs of treating only a small proportion of the epidemic. We describe two approaches for deciding when to start or scale up prevention programs. The standard model is defined by the expected lifetime of the epidemic. A key assumption is that the longer the population is exposed to HIV, the higher its chances of becoming infected and the more severe the consequences of infection. The standard model was used to prioritize resources for HIV control by the UNAIDS Regional Aids Directorates-East and Southern Africa for the period 2003-2009.
Uncertainty in modeling the epidemic
Previous estimates of the magnitude of HIV infections and the burden of AIDS worldwide have often varied substantially, leading to speculation that the epidemic is not responding to the AIDS prevention and treatment interventions that have been deployed. Several factors may have influenced such variation, including:
Modeling social interactions affecting prevention and treatment outcomes
Hormonal contraceptives could potentially be incorporated into care for women with a disease state of limited alternative treatment options in sub-Saharan Africa.
Assessing the efficacy of preventive interventions
A team in Senegal made a massive effort to establish an accurate measure of HIV. They did so by building the world's largest HIV database, the Surveillance, Epidemiology, and End-Stage Disease Surveillance system (SEEDS), on ten of the region's smaller and remote islands.
Characteristics of a Model That Can Support Decisionmakers In Preventing The Spread Of HIV/AIDS
The HIV epidemic is a complex process of transmission, acquisition, and resistance to antiretroviral drugs. Because HIV's transmission process depends heavily on factors outside the control of decision makers, models that model aspects of transmission, acquisition, and resistance are a powerful aid in resource allocation decision making. These models give us an overview of where HIV transmission is occurring and also how to best target our interventions to reduce HIV prevalence. Not all models are suitable for resource allocation purposes, however, because our understanding of HIV transmission is incomplete, the characteristics of each transmission stage are complex, and the definition of what makes an infection "positive" differs depending on the context.
ApM's Editors and Users
In this issue of AIDS Patient Care & AIDS Research, 7(4), 69-84, apM is pleased to feature the introduction of a special section addressing clinicians and AIDS researchers who work on evaluating the role of drugs for HIV prevention and treatment. The ApM staff welcomes and hopes that you will post your comments and suggestions below. If you are interested in becoming a member of the AIDS Patient Care & AIDS Research community, please send a short email to AIDSPatc@aol.com to find out more. In the following months, we will be working with our HIV research community to include topics relevant to their work, including improving counseling of patients and AIDS research, and publication of studies in ApM.
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