The HIV prevention cascade – a new approach to guide HIV prevention programmes

Providing a conceptual framework for HIV prevention cascades and assessing feasibility of empirical measurement with data from east Zimbabwe: a case study.

Garnett GP, Hallett TB, Takaruza A, Hargreaves J, Rhead R, Warren M, Nyamukapa C, Gregson S. Lancet HIV. 2016 Jul;3(7):e297-306. doi: 10.1016/S2352-3018(16)30039-X.

Background: The HIV treatment cascade illustrates the steps required for successful treatment and is a powerful advocacy and monitoring tool. Similar cascades for people susceptible to infection could improve HIV prevention programming. We aim to show the feasibility of using cascade models to monitor prevention programmes.

Methods: Conceptual prevention cascades are described taking intervention-centric and client-centric perspectives to look at supply, demand, and efficacy of interventions. Data from two rounds of a population-based study in east Zimbabwe are used to derive the values of steps for cascades for voluntary medical male circumcision (VMMC) and for partner reduction or condom use driven by HIV testing and counselling (HTC).

Findings: In 2009 to 2011 the availability of circumcision services was negligible, but by 2012 to 2013 about a third of the population had access. However, where it was available only 12% of eligible men sought to be circumcised leading to an increase in circumcision prevalence from 3.1% to 6.9%. Of uninfected men, 85.3% did not perceive themselves to be at risk of acquiring HIV. The proportions of men and women tested for HIV increased from 27.5% to 56.6% and from 61.1% to 79.6%, respectively, with 30.4% of men tested self-reporting reduced sexual partner numbers and 12.8% reporting increased condom use.

Interpretation: Prevention cascades can be populated to inform HIV prevention programmes. In eastern Zimbabwe programmes need to provide greater access to circumcision services and the design and implementation of associated demand creation activities. Whereas, HTC services need to consider how to increase reductions in partner numbers or increased condom use or should not be considered as contributing to prevention services for the HIV-negative adults.

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Editor’s notes: UNAIDS has set an ambitious goal of reducing new adult HIV infections below 500 000 per year by 2020. Achieving this goal relies on increased coverage of primary HIV prevention programmes, including pre-exposure prophylaxis and voluntary medical male circumcision (VMMC). The HIV treatment cascade is a well known tool to monitor the performance of services for people living with HIV, and to identify gaps in care. An HIV prevention cascade could provide a similarly useful tool to inform prevention programmes. The tool would define the steps necessary for an effective HIV prevention programme, estimating the proportion of people lost at each step, and hence identifying the barriers to effective HIV prevention in populations. The authors propose a framework for HIV prevention cascades, differentiating between availability, uptake, adherence, and efficacy.  The framework would estimate the proportion of the population protected by a given strategy or combination of strategies. Population survey data from rural Zimbabwe are used to illustrate the prevention cascade for VMMC and behaviour change driven by HIV testing and counselling (HTC). These data are used to highlight the barriers impacting on reducing HIV incidence. As the authors acknowledge, there are limitations to the cascade approach for HIV prevention. The cascade is more difficult to define and to estimate for HIV prevention than for HIV treatment. In order for the cascade to be useful, it is necessary to have a good understanding of who is at risk of acquiring HIV.  However, the prevention needs of HIV negative adults change over time as people move in and out of risk. Although the authors illustrate the use of the cascade for an individual programme, it is more difficult to assess the combined effect of several prevention strategies. Still, the cascade approach may provide a useful tool to help guide HIV prevention efforts, by identifying gaps and prioritising areas for action.

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