Treatment as Prevention: Do the Individual Prevention Benefits Translate to the Population Level?
Factors Limiting Treatment Coverage and Its Prevention Benefits
While the evidence above provides some indication of a relationship between increased treatment coverage, decreased community viral load and HIV prevention, the null findings -- particularly among gay men and other MSM -- suggest levels of treatment coverage in some populations may be insufficient to reduce HIV incidence. In fact, modelling studies suggest treatment coverage may need to exceed a certain threshold before its prevention benefits are observed.23 Therefore, efforts to further increase the proportion of people on successful treatment may improve HIV prevention efforts.
However, several factors are limiting treatment coverage among populations of people living with HIV. These include 1) the large proportion of people living with HIV who are undiagnosed, 2) poor engagement in HIV care, and 3) recommendations in treatment guidelines.
While treatment coverage has been increasing among HIV-positive people who are diagnosed and know their HIV status, the proportion of people with HIV who are undiagnosed has remained relatively stable in many parts of the world and this is limiting treatment coverage. For example, the Public Health Agency of Canada estimates that approximately 25% of people with HIV in Canada do not know their status (this proportion has not changed significantly over the last decade).24 Unfortunately, undiagnosed individuals cannot benefit from care and treatment, and research suggests they may contribute to the majority of HIV transmissions in a population.25
Poor engagement in HIV care is another barrier to increasing treatment coverage. Diagnosed individuals who are not engaged in HIV care cannot start treatment when they are ready to do so. Also, care is important to support adherence to medications so that treatment can successfully reduce the viral load to undetectable levels. Unfortunately, research suggests many people are not being linked to care after diagnosis and not remaining in care once linked.26
The number of people on treatment is also influenced by how soon an HIV-positive individual is eligible to start treatment once diagnosed and in care. Although many factors determine when someone is offered -- and starts -- treatment, an important one is eligibility recommendations in treatment guidelines. Coincidentally, as we have learned more about the prevention benefits of early treatment, we have also learned more about the importance of early treatment for the health of people living with HIV.27 As a result, over the last several years, guidelines have moved toward recommending increasingly earlier treatment.
For example, in 2009 the World Health Organization guidelines raised the eligibility threshold for starting treatment from 200 to 350 CD4 cells and their new guidelines -- released in 2013 -- increases this threshold to 500 CD4 cells. Furthermore, several major treatment guidelines in the United States -- which previously recommended treatment initiation when the CD4 count dropped below 500 cells -- now recommend that treatment be offered as soon as a person is diagnosed with HIV, regardless of their CD4 count. These guidelines include those produced by the Department of Public Health in San Francisco (revised in 2010), the Department of Health and Human Services (revised in 2012), and the International Antiviral Society-USA (revised in 2012).
Therefore, the evidence available so far cannot answer the question of what the potential prevention benefit of treatment might be if the proportion of undiagnosed people was much smaller, engagement in HIV care (including support for adherence) was improved, and more people were on therapy due to new treatment guidelines.
Seek, Test and Treat -- Maximizing the Prevention Benefits
Promisingly, modelling studies suggest the impact of treatment on HIV incidence could be significantly improved by increasing rates of HIV testing, offering treatment earlier and improving linkage to care, retention in care and treatment adherence.28-31 The impact in these models varies from moderate to dramatic (depending on the assumptions used) and it is clear that treatment alone will not be able to end the epidemic.
These modelling studies -- and the other evidence described above -- have led to the concept of a "test and treat" or "seek, test and treat" strategy. This strategy involves proactive efforts to increase the proportion of people who are on successful treatment by improving engagement in HIV testing, care and support, and treatment services (also known as the treatment cascade). These efforts not only have the potential to prevent HIV transmissions, but also improve the health of people living with HIV.
However, several questions currently remain unanswered with regards to "seek, test and treat" approaches and the use of treatment as a public health HIV prevention strategy. For example, is it feasible to significantly decrease the proportion of people who are undiagnosed and increase the proportion who are on successful treatment? What is needed to do this and how much can it reduce HIV incidence? There are also unanswered questions regarding the acceptability, sustainability and affordability of this approach.
Several large coordinated "seek, test and treat" initiatives are ongoing to answer these questions, although they have yet to be fully evaluated. These include:
Between 2010 and 2013, a pilot project called the Seek and Treat for Optimal Prevention of HIV/AIDS (STOP) Project funded more than three dozen initiatives in Vancouver and Prince George. One of the aims of the overall project was to reduce the number of new HIV infections by taking an active public health approach to finding people living with HIV (either newly diagnosed or lost to care), bringing them into HIV treatment programs, and supporting them to stay on treatment.
While STOP is sometimes referred to as "seek and treat," it also addresses individual and community needs across the full continuum of care, including prevention, engagement, and linkage to care and support. It has done this by expanding opportunities for everyone to get tested for HIV through routine offers of testing in hospitals and family practice and by offering testing in locations that cater to people at ongoing or higher risk for HIV infection; by improving the system of linkage to care and treatment, both for HIV and mental health and addictions, through the STOP Outreach Team and the Peer Navigation Program; and by providing expanded opportunity to receive HIV primary care and adherence support in community settings.
Evaluation of the pilot project is ongoing. Results so far show that the number of patients engaged in care has increased by 39% since the beginning of STOP. The mean community viral load has also declined.32 In April 2013, the Government of British Columbia announced it was funding the province-wide roll out of the STOP Project.
San Francisco's HIV/AIDS Strategy (2010-2014) is a system-wide approach to HIV prevention, treatment, care and support. The goals of the strategy are to optimize the health outcomes of people living with HIV and reduce the number of new HIV transmission by suppressing community viral load. The strategy integrates public health services, primary care, and the services of community-based HIV/AIDS service organizations -- and includes a research component -- in order to reduce the cracks through which people seeking services may fall. The strategy, set to be completed in 2014, has not yet been evaluated.
In order to improve health outcomes for people living with HIV and reduce the number of new infections, San Francisco rolled out a city-wide approach. This approach is based on early diagnosis, engagement, linkage to care, and treatment adherence support. It includes promoting routine testing in medical settings and updating testing protocols and policies in community-based settings (counselling is no longer a prerequisite to get an HIV test and populations at increased risk are encouraged to test every three to six months). It also includes providing intensive prevention interventions to people at elevated risk for HIV infection and providing appropriate services for, and a universal offer of treatment to, those already living with HIV.
What Can Frontline Organizations Do?
Treatment has an important role to play in strengthening HIV prevention efforts and should be considered an important component of a comprehensive approach to HIV prevention. However, it will not be able to end the epidemic alone. Community-based organizations will continue to play an important role in the implementation of other biomedical, behavioural and structural HIV prevention strategies, such as the provision of condoms and education, risk-reduction counselling, post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP), stable housing, and mental health services.
Frontline organizations should also think about the role they can play in maximizing the prevention benefit of treatment and ensuring individual rights are respected. This may include tools to support informed decision making, treatment readiness, and the doctor-patient relationship; use of innovative approaches to reaching the undiagnosed, improving engagement in care, and supporting adherence; and efforts to improve STI prevention and treatment (as untreated STIs in either partner may offset the prevention benefit of treatment).
This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication Prevention in Focus: Spotlight on Programming and Research. Visit CATIE's Web site to find out more about their activities, publications and services.
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