What is evidence-based HIV prevention?

This section introduces the evidence for the effectiveness of interventions that encourage people to adopt behaviours that reduce their risk of HIV infection. It also looks at evidence for interventions designed to help HIV-positive people to minimise their risk of transmitting HIV.

There is a demand amongst funders and practitioners for evidence that particular HIV-prevention methods work. The phrase ‘evidence-based prevention' has been coined to describe the need for HIV-prevention activities to be developed in line with evidence regarding risk factors and outcomes.

In general, calls for an evidence-based approach follows calls in NHS clinical practice for better outcomes through the adoption of ‘evidence-based medicine’, i.e. interventions whose efficacy has been demonstrated in sound clinical trials.

In particular, there is evidence that condom use is at best static and at worst declining amongst some at-risk populations, notably gay men in richer countries.^1,2 This has led to demands both for better and more assertive behavioural interventions, on the one hand, and increased emphasis on treatment as prevention and biomedical prevention, on the other. This is a much-politicised area and, therefore, one in which gathering evidence on the effectiveness of interventions may help shed light in heated debates.

The call for evidence-based prevention is only part of a wider demand that health-promotion activities, psychotherapy and counselling, and other non-drug-based interventions are subjected to the same kind of scrutiny as drug treatments. The potential for harming patients with untested drug treatments is obvious. The same applies to biomedical-prevention methods. For example, the spermicide nonoxynol-9 killed HIV in the test tube, but was found to facilitate transmission in real life.³

Behavioural-prevention programmes that are not evidence based and well thought out are less likely to do harm and may simply waste money. However, there are occasional examples of ones that produce significantly worse health outcomes than doing nothing. In a recent meta-analysis of adherence interventions, for instance,⁴ most interventions were positive or neutral in their effect. There was, though, one trial in which 40 participants wrote about an optimistic future in which they would only take one medication a day; this had a significantly negative effect, with nearly 60% worse adherence in the intervention group.

One large meta-analysis⁵ of behavioural interventions in HIV prevention, which we examine in more detail below, found that programmes that used threat-inducing arguments to encourage condom use (such as the fear of pregnancy) and normative arguments (‘everyone else does it, you should too’) had significant negative effects across participants as a whole, though there were exceptions.

It is, therefore, important to review the effectiveness of prevention programmes, as to do otherwise would not only waste public money, but might increase HIV infections.

This section reviews:

• How and why we measure whether HIV-prevention efforts have worked, and issues in measuring effectiveness.
• The evidence provided by some large systematic reviews and meta-analyses of HIV-prevention programmes.
• The underlying philosophies of HIV prevention: how and why people change their behaviour.