Academic journal article Bulletin of the World Health Organization

Understanding the Modes of Transmission Model of New HIV Infection and Its Use in Prevention Planning/ Comprendre le Modele Des Modes De Transmission Des Nouvelles Infections Par le VIH et Son Utilisation Dans Les Plans De prevention/Entender El Modelo De Los Modos De Transmision De Las Infecciones Nuevas Por VIH Y Su USO En Los Planes De Prevencion

Academic journal article Bulletin of the World Health Organization

Understanding the Modes of Transmission Model of New HIV Infection and Its Use in Prevention Planning/ Comprendre le Modele Des Modes De Transmission Des Nouvelles Infections Par le VIH et Son Utilisation Dans Les Plans De prevention/Entender El Modelo De Los Modos De Transmision De Las Infecciones Nuevas Por VIH Y Su USO En Los Planes De Prevencion

Article excerpt

Introduction

In the current global financial climate, it is more important than ever that effective resource allocation for the control of human immunodeficiency virus (HIV) infection is based on informed, strategic decision-making. Planning HIV prevention programmes requires up-to-date information on the likely sources of new infections and mathematical modelling provides a framework for understanding epidemic patterns and for highlighting priority areas for prevention. Various models of HIV epidemics, in particular the modes of transmission (MOT) model recommended by the Joint United Nations Programme on HIV/AIDS (UNAIDS), (1) are used to increase understanding and to assist national planning. (2-10)

When constructing a model, it is important to include adequate detail to address the questions posed. Superfluous detail reduces the transparency of the model and can make it more difficult to estimate model parameters reliably, whereas excluding important details can lead to erroneous conclusions. The MOT model was developed in 2002 and was designed to focus on identifying who is at risk of infection rather than on the broad categorization of the type of epidemic (i.e. low-level, concentrated, generalized or hyperendemic). (11) Its aim was to provide better information for strategic planning of disease prevention.

Unlike models that are region-specific (e.g. the Asian Epidemic Model) (12) or country-specific (e.g. the Actuarial Society of South Africa model, (13) used primarily in South Africa but also in other countries in southern Africa), the MOT model was designed to be easy to use and can be applied in any epidemic setting. It differs from other approaches, such as the Estimation and Projection Package (14) curve-fitting approach embedded within the Spectrum modelling software, (15) which estimates and projects HIV prevalence and incidence from surveillance data and does not aim to take mechanisms of infection into account.

Use of the MOT model at the country level was recommended in 2008 as part of a synthesis process supported by UNAIDS and the World Bank Global HIV/AIDS Monitoring and Evaluation Team in southern and eastern Africa), (16,17) consistent with the UNAIDS "know your epidemic, know your response" strategy. (18) This approach emphasizes the importance of understanding, at the local level, which subpopulations are most at risk of HIV infection and which risk behaviours may facilitate transmission and of using this information to tailor national responses.

When evaluating the performance of a model that is widely used to assist countries in decision-making, it is important to consider the perspective and experience of individuals involved in the modelling process, including those involved in developing and implementing the model, those who rely on the model results for decision-making and the normative agencies that help support the modelling process. In April 2011, the HIV Modelling Consortium (participants are listed in the acknowledgements section) gathered together stakeholders involved in different stages of the modelling process to review both the methods used for estimating sources of HIV infection and the MOT process. (19) The impetus for this manuscript originated from discussions at this meeting; one outcome of the meeting was a manuscript that described the strengths and limitations of the MOT process.

Our intention was to strengthen future use of the MOT model by reviewing its principle features in detail and by summarizing feedback from previous applications. Specifically, we aimed to clarify the model paradigm, to review the model structure and data requirements and to propose questions that can be used to guide interpretation of the model results.

Modes of transmission model

The MOT model uses information on the current distribution of prevalent infections in a population and assumptions about patterns of risk behaviour within different risk groups to calculate the expected distribution of new adult HIV infections in the following year in terms of the mode of exposure. …

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