Academic journal article Bulletin of the World Health Organization

The Effectiveness of HIV Prevention and the Epidemiological Context

Academic journal article Bulletin of the World Health Organization

The Effectiveness of HIV Prevention and the Epidemiological Context

Article excerpt

Voir page 1130 le resume en francais. En la pagina 1130 figura un resumen en espanol.

Introduction

Public health interventions to prevent new human immunodeficiency virus (HIV) infections can be targeted at different risk behaviours (e.g. heterosexual sexual intercourse, injecting drug use), different aspects of a given risk behaviour (e.g. heterosexual sexual intercourse: age at sexual debut, levels of pre- and extramarital sexual intercourse, condom use, etc.), and different at-risk populations (e.g. prostitutes, adolescents and school youth, young women). Interventions can range from education to promote behaviour change, to treatment of bacterial sexually transmitted infections (STIs) that enhance HIV transmission, to social marketing of condoms. The impact of such interventions depends very much upon the local context, in terms of risk behaviour, attitudes to risk, prevalence of cofactor STIs, stage of the HIV epidemic, existing health services, etc. Intervention design must take the local context into account.

Implementation of interventions

The implementation of an intervention to prevent the spread of HIV can be considered to have an immediate `outcome' in terms of a change in risk behaviour or the riskiness of that behaviour, and a consequent `impact' on HIV incidence (Fig. 1). The likelihood of a significant outcome in this sense is determined by the socioeconomic, cultural and legislative context, and the existing public health service infrastructure. For example, an intervention that promotes access to educational material about safer sex may have different outcomes, in terms of changes in sexual risk behaviour, in different localities depending on community attitudes to sex. Whether or not the outcome of an intervention translates into an impact on HIV incidence depends on the epidemiological context. Although a significant programme outcome implies a relative reduction in HIV incidence, the relations between these two parameters are complex and nonlinear (1,2). Even an intervention with a large outcome may have minimal impact on HIV incidence if implemented late in the HIV epidemic or targeted at the wrong people (3). Dramatic increases in condom distribution may have very little impact on HIV spread until use during sexual intercourse is close to 100% in high-risk partnerships (4). Researchers and policy advisers must therefore be very careful in advocating interventions that have been shown to be successful using only measures of programme outcome and not impact (1).

[FIGURE 1 OMITTED]

Epidemiological context

The epidemiological context will depend on the intervention of interest, but can be broadly defined as the current state and trends in the behavioural and biological factors that determine the transmission dynamics of a given disease and the impact of a specified intervention. The appropriateness of an intervention to the local context can be assessed by the use of intervention trials, most rigorously by randomized controlled trials (RCTs). However, for the majority of HIV/AIDS programme managers this is not an option, and intervention selection typically proceeds by a process of analogy: those interventions that have proved effective in similar socioeconomic and epidemiological contexts are taken as models for the local intervention. This process often results in the selection of those interventions shown to be effective by the few published and well-publicized RCTs. When the same intervention carried out in different contexts has different impacts, confusion can arise over its appropriateness. For example, the reduction in HIV incidence resulting from an intervention offering improved syndromic treatment of cofactor STIs in the United Republic of Tanzania was not replicated by a community-wide STI treatment programme in Uganda (5,6). Although these interventions implemented STI treatment in different ways, a significant cause of their different impacts is likely to have been the different contexts (7). …

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