HIV This Week

Hallett TB, White PJ, Garnett GP. The appropriate evaluation of HIV prevention interventions: from experiment to full scale implementation. Sex Transm Infect 2007 Jan 10[Epub ahead of print]. http://sti.bmj.com/cgi/rapidpdf/sti.2006.023663v1

Preventing HIV infection is an essential goal in tacking the HIV pandemic. Remarkably little is known about how best to reduce HIV incidence because the majority of trials focus on the reduction of risk behaviours and assume an effect on HIV incidence. Hallett and colleagues discuss the evidence for the effectiveness of HIV prevention strategies, exploring the different types of evidence available, including individual and community randomised controlled trials and observational studies. Whilst providing a gold standard for evidence, trials have been limited in their scope and are difficult to interpret and generalise. There have been examples of national level successes in preventing HIV which have been detected in surveillance data and understood through behavioural and modelling studies. These have the advantage of being to scale and indicating effectiveness rather than efficacy. The authors conclude that whilst randomised trials are important because of their scientific rigor, it is also important that evidence from observational epidemiology is not overlooked. Only if good quality and consistent data are available can the history of the HIV epidemic be appropriately analysed.

Editors’ note: There is a long history of debating the value of observational versus randomised controlled trial evidence. Both are valuable, including negative trial results which are often not published. More attention needs to be paid to qualitative methodologies which not only can produce information that helps explain quantitative findings but also can guide policy making and decisions about programming.

Lyles CM, Kay LS, Crepaz N, Herbst JH, Passin WF, Kim AS, Rama SM, Thadiparthi S, DeLuca JB, Mullins MM; HIV/AIDS Prevention Research Synthesis Team. Best-evidence interventions: findings from a systematic review of HIV behavioral interventions for US populations at high risk, 2000-2004. Am J Public Health 2007;97:133-43.

The Centers for Disease Control and Prevention's HIV/AIDS Prevention Research Synthesis Team conducted a systematic review of US-based HIV behavioural intervention research literature from 2000 through 2004 to identify interventions demonstrating best evidence of efficacy for reducing HIV risk. The authors used standard systematic review methods. Each eligible study was reviewed on the basis of Prevention Research Synthesis Team efficacy criteria that focused on 3 domains: study design, implementation and analysis, and strength of evidence. Eighteen interventions met the criteria for best evidence. Four targeted HIV-positive individuals. Of those targeting populations at risk for HIV, 4 targeted drug users, 6 targeted adults at risk because of heterosexual behaviours only, 2 targeted men who have sex with men, and 2 targeted youths at high risk. Eight interventions focused on women, and 13 had study samples with more than 50% minority participants. Significant intervention effects included increased condom use and reductions in unprotected sexual intercourse, number of sexual partners, injection drug use or needle sharing, and newly acquired sexually transmitted infections. The authors conclude that most of the best-evidence interventions are directly applicable for populations in greatest need of effective prevention programmes; however, important gaps still exist.

 Editors’ note: Scaling up now what is known to be effective and addressing structural determinants, while conducting research to fill remaining knowledge gaps, constitute critical elements in the path to HIV prevention success.

Lewis JJ, Donnelly CA, Mare P, Mupambireyi Z, Garnett G, Gregson S. Evaluating the proximate determinants framework for HIV infection in rural Zimbabwe. Sex Transm Infect 2007 Jan 10 [Epub ahead of print]. http://sti.bmj.com/cgi/rapidpdf/sti.2006.023671v1

Risk factors for HIV infection can act at one of several causal levels, making interpretation of results problematic. One suggested solution has been a proximate determinants framework, analogous to that used in the study of fertility and child survival. In this framework, risk factors are grouped into "underlying", "proximate" and "biological" determinants. Lewis and colleagues carried out a baseline, cross-sectional survey of HIV serostatus and potential risk factors among 9480 adults in Zimbabwe. Associations were assessed separately for men and women using logistic regression models; data were only included for those who reported sexual debut. The predictive ability of proximate determinants describing both individual and partnership characteristics was assessed along with the predictive ability of the underlying determinants. The significance of the underlying determinants once adjusted for proximate determinants was then evaluated. Finally the relationship between the underlying determinants and some of the key proximate determinants was explored. The two most important proximate determinants for both men and women were lifetime number of sexual partners and symptoms of sexually transmitted infections (p<0.001). After adjustment for all proximate determinants, some underlying determinants were still significant, particularly age group, marital status and community (<0.001). The authors conclude that whilst the proximate determinants could explain the action of many of the underlying determinants, several of the underlying determinants remained significant after adjustment for the proximate determinants. This suggests that the proximate determinants were not measured completely. One of the most important determinants of an individual's risk of HIV infection is the HIV status of their sexual partners. This was not measured in this survey and may be related to the individual's age (as a predictor for the age of the partner), marital status and community prevalence. Hence, partner's HIV status will be measured in a subsequent survey of this cohort.  

Editors’ note: It has often been said that, although they are highly interrelated, the prevalence of HIV in your bed is more important than that of the community in which you live in determining your risk of HIV exposure. Unknown sero-discordance in stable, exclusive partnerships is responsible for a significant amount of HIV transmission in many settings around the world. Effectively assisting couples to learn their HIV status together in a supportive fashion and to implement and maintain safer sex practices to reduce their risk is key to addressing this aspect of the epidemic.