From Prevention in Focus, Fall 2013
Treatment as prevention: do the individual prevention benefits
translate to the population level?
By James Wilton and Logan Broeckaert
Antiretroviral treatment can dramatically improve the long-term health of someone living with HIV. It can also reduce
their risk of onward HIV transmission. Therefore, efforts to increase the number of HIV-positive people who are on
treatment may – as a secondary benefit to improving health – help curb the number of new HIV infections in Canada
and around the world. The idea that treatment may be able to prevent HIV transmission at the population level and
have an impact on the HIV epidemic is commonly referred to as “treatment as prevention.” This has led to the
concept of a “test and treat” or “seek, test and treat” strategy: a public health approach with the goal of maximizing
the prevention benefits of treatment by increasing treatment coverage and decreasing community viral load.
Treatment provides prevention benefits at the individual level by reducing viral
load
Antiretroviral treatment (ART) can reduce the viral load in the blood, semen, vaginal fluid and rectal fluid to very low
levels (undetectable by current viral load tests) and this can reduce an individual’s risk of HIV transmission. This was
demonstrated in a randomized controlled study known as HPTN 052 where treatment reduced the risk of HIV
1
transmission by 96% among heterosexual serodiscordant couples. However, it is important to point out that
couples in this study reported mostly having vaginal sex and were provided with regular adherence counselling, viral
load tests, testing and treatment for sexually transmitted infections (STIs), and prevention counselling and free
condoms. All of these may have helped maximize the prevention benefit of treatment.
While it’s unclear if the same reduction in risk applies to other populations – such as couples who do not receive
these ongoing services, people in casual relationships, gay men and other men who have sex with men (MSM), and
2
people who use injection drugs – it is generally thought that ART reduces HIV risk to some extent.
[UPDATE: In March 2014, a preliminary analysis of an ongoing study ( the PARTNER study) reported the first direct
evidence that ART can significantly reduce HIV risk for gay men and other MSM.]
Prevention benefits at a population level?
Since treatment has prevention benefits at the individual level, it makes sense to think it may also have prevention
benefits at the population level. In other words, increasing the number of HIV-positive people on treatment could
lower the total amount of virus circulating in a community (also known as community viral load) and lead to a
reduction in the number of new HIV infections.
So what evidence do we have? As HIV testing and treatment have become more accessible over the past decade,
the number of HIV-positive people on treatment has been steadily increasing in most parts of the world. Whether
the prevention benefits of treatment have already translated to the population level (prior to the implementation of
any specific “seek, test and treat” strategies) can be explored by looking at whether increases in treatment
coverage – and subsequent decreases in community viral load – have coincided with a reduction in new HIV
diagnoses or estimated number of new HIV infections (also known as HIV incidence).
However, the evidence available so far is observational and has its limitations. Even if it is found that the number of
HIV diagnoses (or HIV incidence) decreased in a population as more people accessed HIV treatment (a positive
finding), it is difficult to know exactly why this happened. For example, a decrease in HIV diagnoses may have been
the direct result of increased treatment coverage or it may have been the result of other HIV prevention
interventions that were implemented at the same time.
Conversely, if it is found that HIV diagnoses stayed the same or increased as treatment coverage increased (a null
finding), it is also difficult to know why this happened. For example, this may mean that treatment did not have
prevention benefits or, on the other hand, it is possible that treatment did prevent transmissions but improvements
in HIV testing services led to the identification of more cases of HIV and made it appear that treatment did not have
an effect.
Furthermore, community viral load may not be a good indicator of overall infectiousness in a population. This is
because community viral load is generally calculated using the viral load measurements of people living with HIV who
are diagnosed and in care. Therefore, this measure does not include those who are undiagnosed or not in care and,
as a result, may not reflect the viral load among all HIV-positive people in a community.
Because of these limitations, the evidence available so far should be viewed cautiously.
Below is a summary of the evidence of whether treatment has had a prevention impact in different populations.
Heterosexual populations in low-to-middle income countries
Globally, several countries have experienced decreases in estimated HIV incidence as treatment coverage has
3
increased, suggesting treatment may be having a prevention impact. According to UNAIDS, HIV incidence
decreased by more than 25% in 39 countries – the majority of which were low-to-middle income, in sub-Saharan
Africa, and have generalized heterosexual epidemics – between 2001 and 2011. During the same time period,
treatment coverage increased dramatically in many of these countries. For example, treatment coverage in subSaharan Africa increased by more than 100-fold. Although other HIV prevention efforts were also dramatically
scaled up during this time, some experts think increased treatment coverage may have contributed to the decrease
4
in new HIV infections.
Furthermore, a recent study of a group of over 16,000 HIV-negative individuals in a rural area in South Africa found
that for every 1% increase in ART coverage among people living with HIV, the risk of HIV infection decreased by
1.4%.Furthermore, an HIV-negative person living in a community with treatment coverage of 30–40% was on
5
average 38% less likely to become infected than if they were living in a community with coverage less than 10%.
People who use injection drugs in British Columbia
“Treatment as prevention” may be occurring among people who use injection drugs in British Columbia. Between
1996 and 2009, the number of people with HIV on ART in B.C. increased from 837 to 5413 (a 550% increase) and –
6
in the same time period – the number of new HIV diagnoses fell from 702 to 338 per year (a 50% decrease).
However, HIV diagnoses only decreased among people who use injection drugs and not among non-injection drug
using populations. In a separate Vancouver-based study, decreased community viral load was associated with
7
reduced estimated HIV incidence among a group of HIV-negative drug users.
Even though reductions were observed among injection drug users in these studies, some experts have noted that
8
other services for this population were improved during this time and may have contributed to this decrease. For
example, the Vancouver-based supervised injection site known as Insite opened its doors in 2003.
Gay men and other MSM in high-income countries
“Treatment as prevention” does not appear to be happening among many populations of gay men and other MSM.
In most high-income countries, estimated HIV incidence among MSM is remaining stable or continuing to increase
9 10
despite increases in treatment coverage and decreases in community viral load. ,
For example, in England and Wales, treatment uptake among diagnosed MSM in care rose from 69% in 2001 to
11 12
80% in 2010 and an estimated 53% of all MSM living with HIV in 2010 had an undetectable viral load. , However,
the annual number of new HIV diagnoses remained unchanged during this time period. Treatment coverage levels
among MSM in France and Australia are similar to those in the UK but the number of new HIV diagnoses are
13 14
continuing to increase in these countries. , While the number of new HIV infections does not appear to be
decreasing, experts think HIV incidence among MSM in many high-income countries would be higher if not for
15 16 17 18
increased treatment coverage. , , ,
An exception is the experience of San Francisco, where increased treatment coverage and decreased community
19
viral load has been associated with a reduction in new HIV diagnoses. Between 2004 and 2008 the proportion of
diagnosed HIV-positive MSM in care with an undetectable viral load increased from 45% to 78% (resulting in a
decline in community viral load) and the number of new HIV diagnoses decreased from 798 to 434 (a 54%
decrease). A more recent study – extending this time period to 2011 – supports the idea that “treatment as
20
prevention” is occurring among gay men in this city.
Other studies
Increased treatment coverage has not reduced HIV incidence in Washington, D.C. Between 2004 and 2008, the
proportion of diagnosed HIV-positive individuals in care with an undetectable viral load increased from 15% to 58%,
21
the community viral load decreased, but the annual number of new HIV diagnoses did not change.
In Southern Alberta, treatment coverage among people living with HIV in care increased from 62% to 81% between
2001 and 2010, while the proportion of people with a viral load of less than 200 copies/ml increased from 49% to
72%. Despite the large increase in treatment coverage and viral suppression, community viral load surprisingly
22
remained stable and the number of new HIV diagnoses increased.
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
23
benefits are observed. 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
24
significantly over the last decade).
Unfortunately, undiagnosed individuals cannot benefit from care and treatment,
25
and research suggests they may contribute to the majority of HIV transmissions in a population.
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
26
once linked.
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
27
treatment for the health of people living with HIV. 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
28 29 30 31
treatment adherence. , , , 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:
Vancouver
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
32
increased by 39% since the beginning of STOP. The mean community viral load has also declined. In April 2013,
the Government of British Columbia announced it was funding the province-wide roll out of the STOP Project.
San Francisco
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).
Resources
Community consensus statement on the use of antiretroviral therapy in preventing HIV transmission – European
AIDS Treatment Group, NAM
References
1.
Cohen MS, Chen YQ, McCauley M, Gamble T, Hosseinipour MC, Kumarasamy N, et al. Prevention of HIV-1 infection with early antiretroviral
therapy. New England Journal of Medicine . 2011 Aug 11;365(6):493–505.
2.
World Health Organization. WHO and U.S. NIH Working Group Meeting on Treatment for HIV Prevention among MSM: What Additional
Evidence is Required. Geneva; 2011 Nov.
3.
UNAIDS. Report on the Global AIDS Epidemic. 2012.
4.
Hankins C. Overview of the current state of the epidemic. Current HIV/AIDS Reports . 2013 Jun;10(2):113–23.
5.
Tanser F, Bärnighausen T, Grapsa E, Zaidi J, Newell M-L. High coverage of ART associated with decline in risk of HIV acquisition in rural
KwaZulu-Natal, South Africa. Science . 2013 Feb 22;339(6122):966–71.
6.
Montaner JSG, Lima VD, Barrios R, Yip B, Wood E, Kerr T, et al. Association of highly active antiretroviral therapy coverage, population viral
load, and yearly new HIV diagnoses in British Columbia, Canada: a population-based study. Lancet . 2010 Aug 14;376(9740):532–9.
7.
Wood E, Kerr T, Marshall BDL, Li K, Zhang R, Hogg RS, et al. Longitudinal community plasma HIV-1 RNA concentrations and incidence of
HIV-1 among injecting drug users: prospective cohort study. British Medical Journal . 2009;338:b1649.
Wilson DP. HIV treatment as prevention: natural experiments highlight limits of antiretroviral treatment as HIV prevention. PLoS
Medicine . 2012;9(7):e1001231.
9.
Beyrer C, Sullivan PS, Sanchez J, Dowdy D, Altman D, Trapence G, et al. A call to action for comprehensive HIV services for men who have
sex with men. Lance t. 2012 Jul 28;380(9839):424–38.
10. Sullivan PS, Carballo-Diéguez A, Coates T, Goodreau SM, McGowan I, Sanders EJ, et al. Successes and challenges of HIV prevention in
men who have sex with men. Lancet . 2012 Jul 28;380(9839):388–99.
8.
11. Birrell PJ, Gill ON, Delpech VC, Brown AE, Desai S, Chadborn TR, et al. HIV incidence in men who have sex with men in England and Wales
2001-10: a nationwide population study. Lancet Infectious Diseases . 2013 Apr;13(4):313–8.
12. Delpech V, Yin Z, Kall M, Brown A. The United Kingdom’s National Health Service (NHS) provides excellent access to high quality HIV
care: results from a national cohort. XIX International AIDS Conference. 2012 Jul 22;Abstract MOPDC0301.
13. Supervie V, Costagliola D. The Spectrum of Engagement in HIV Care in France: Strengths and Gaps. 20th CROI Conference. 2013 Mar
3;Abstract 1030.
14. Law MG, Woolley I, Templeton DJ, Roth N, Chuah J, Mulhall B, et al. Trends in detectable viral load by calendar year in the Australian HIV
observational database. Journal of the International AIDS Society . 2011;14:10.
15. Phillips AN, Cambiano V, Nakagawa F, Brown AE, Lampe F, Rodger A, et al. Increased HIV incidence in men who have sex with men
despite high levels of ART-induced viral suppression: analysis of an extensively documented epidemic. PLoS ONE . 2013;8(2):e55312.
16. Van Sighem A, Vidondo B, Glass TR, Bucher HC, Vernazza P, Gebhardt M, et al. Resurgence of HIV infection among men who have sex
with men in Switzerland: mathematical modelling study. PLoS ONE . 2012;7(9):e44819.
17. Van Sighem A, Jansen I, Bezemer D, De Wolf F, Prins M, Stolte I, et al. Increasing sexual risk behaviour among Dutch men who have sex
with men: mathematical models versus prospective cohort data. AIDS . 2012 Sep 10;26(14):1840–3.
18. Cowan SA, Gerstoft J, Haff J, Christiansen AH, Nielsen J, Obel N. Stable incidence of HIV diagnoses among Danish MSM despite increased
engagement in unsafe sex. Journal of Acquired Immune Deficiency Syndromes . 2012 Sep 1;61(1):106–11.
19. Das M, Chu PL, Santos G-M, Scheer S, Vittinghoff E, McFarland W, et al. Decreases in community viral load are accompanied by
reductions in new HIV infections in San Francisco. PLoS ONE . 2010;5(6):e11068.
20. Raymond HF, Chen Y-H, Ick T, Scheer S, Bernstein K, Liska S, et al. A new trend in the HIV epidemic among men who have sex with men,
San Francisco, 2004-2011. Journal of Acquired Immune Deficiency Syndromes . 2013 Apr 15; 62(5):584–9).
21. Castel AD, Befus M, Willis S, Griffin A, West T, Hader S, et al. Use of the community viral load as a population-based biomarker of HIV
burden. AIDS . 2012 Jan 28;26(3):345–53.
22. Krentz HB, Gill MJ. The Effect of Churn on ‘Community Viral Load (CVL) in a well defined regional population. Journal of Acquired Immune
Deficiency Syndromes . 2013 May. doi: 10.1097/QAI.0b013e31829cef18.
23. Ramadanovic B, Vasarhelyi K, Nadaf A, Wittenberg RW, Montaner JSG, Wood E, et al. Changing Risk Behaviours and the HIV Epidemic: A
Mathematical Analysis in the Context of Treatment as Prevention. PLoS ONE . 2013;8(5):e62321.
24. Government of Canada PHA of C. HIV/AIDS Epi Updates - July 2010 - Public Health Agency of Canada [Internet]. [cited 2011 May 12].
Available from: http://www.phac-aspc.gc.ca/aids-sida/publication/epi/2010/2-eng.php
25. Marks G, Crepaz N, Senterfitt JW, Janssen RS. Meta-analysis of high-risk sexual behavior in persons aware and unaware they are infected
with HIV in the United States: implications for HIV prevention programs. Journal of Acquired Immune Deficiency Syndromes . 2005 Aug
1;39(4):446–53.
26. Gardner EM, McLees MP, Steiner JF, del Rio C, Burman WJ. The Spectrum of Engagement in HIV Care and its Relevance to Test-and-Treat
Strategies for Prevention of HIV Infection. Clinical Infectious Diseases . 2011 Mar 1;52(6):793–800.
27. Siegfried N, Uthman OA, Rutherford GW. Optimal time for initiation of antiretroviral therapy in asymptomatic, HIV-infected, treatmentnaive adults. Cochrane Database of Systematic Reviews Online . 2010;(3):CD008272.
28. Sorensen SW, Sansom SL, Brooks JT, Marks G, Begier EM, Buchacz K, et al. A mathematical model of comprehensive test-and-treat
services and HIV incidence among men who have sex with men in the United States. PLoS ONE . 2012;7(2):e29098.
29. Charlebois ED, Das M, Porco TC, Havlir DV. The effect of expanded antiretroviral treatment strategies on the HIV epidemic among men
who have sex with men in San Francisco. Clinical Infectious Diseases . 2011 Apr 15;52(8):1046–9.
30. Walensky RP, Paltiel AD, Losina E, Morris BL, Scott CA, Rhode ER, et al. Test and treat DC: forecasting the impact of a comprehensive HIV
strategy in Washington DC. Clinical Infectious Diseases . 2010 Aug 15;51(4):392–400.
31. Sood N, Wagner Z, Jaycocks A, Drabo E, Vardavas R. Test-and-Treat in Los Angeles: A Mathematical Model of the Effects of Test-and-Treat
for the Population of Men Who Have Sex With Men in Los Angeles County. Clinical Infectious Diseases . 2013 Jun;56(12):1789–96.
32. Sandhu J, Chu T, Demlow E, MacDonald L, Heath K, Yip B, et al. Measuring the impact of enhanced testing and treatment on the HIV
epidemic in Vancouver, Canada. Oral presentation at the 22nd Annual Canadian Conference on HIV/AIDS Research; Vancouver; 2013 Apr
11-14.
About the author(s)
James Wilton is the coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James is currently
completing his master’s degree of Public Health in Epidemiology at the University of Toronto and has completed an
undergraduate degree in microbiology and immunology at the University of British Columbia.
Logan Broeckaert holds a Master’s degree in History and is currently a researcher/writer at CATIE. Before joining
CATIE, Logan worked on provincial and national research and knowledge exchange projects for the Canadian AIDS
Society and the Ontario Public Health Association.
Produced By:
555 Richmond Street West, Suite 505, Box 1104
Toronto, Ontario M5V 3B1 Canada
Phone: 416.203.7122
Toll-free: 1.800.263.1638
Fax: 416.203.8284
www.catie.ca
Charitable registration number: 13225 8740 RR
Disclaimer
Decisions about particular medical treatments should always be made in consultation with a qualified medical
practitioner knowledgeable about HIV- and hepatitis C-related illness and the treatments in question.
CATIE provides information resources to help people living with HIV and/or hepatitis C who wish to manage their own
health care in partnership with their care providers. Information accessed through or published or provided by
CATIE, however, is not to be considered medical advice. We do not recommend or advocate particular treatments
and we urge users to consult as broad a range of sources as possible. We strongly urge users to consult with a
qualified medical practitioner prior to undertaking any decision, use or action of a medical nature.
CATIE endeavours to provide the most up-to-date and accurate information at the time of publication. However,
information changes and users are encouraged to ensure they have the most current information. Users relying
solely on this information do so entirely at their own risk. Neither CATIE nor any of its partners or funders, nor any
of their employees, directors, officers or volunteers may be held liable for damages of any kind that may result from
the use or misuse of any such information. Any opinions expressed herein or in any article or publication accessed
or published or provided by CATIE may not reflect the policies or opinions of CATIE or any partners or funders.
Information on safer drug use is presented as a public health service to help people make healthier choices to
reduce the spread of HIV, viral hepatitis and other infections. It is not intended to encourage or promote the use or
possession of illegal drugs.
Permission to Reproduce
This document is copyrighted. It may be reprinted and distributed in its entirety for non-commercial purposes
without prior permission, but permission must be obtained to edit its content. The following credit must appear on
any reprint: This information was provided by CATIE (the Canadian AIDS Treatment Information Exchange). For
more information, contact CATIE at 1.800.263.1638.
© CATIE
Production of this content has been made possible through a financial contribution from the Public Health Agency of
Canada.
Available online at:
http://www.catie.ca/en/pif/fall-2013/treatment-prevention-do-individual-prevention-benefits-translate-populationlevel