HIV in Canada: A primer for service providers

Effective treatment of people living with HIV

Key Points

  • Effective treatment of people living with HIV can reduce the viral load to undetectable levels and lower the risk of HIV transmission.
  • There may still be a risk of HIV transmission when the viral load is undetectable because there is still virus in the bodily fluids.
  • Treatment as a form of prevention is an important population-level approach to prevention.

Viral load is one of the most important factors influencing the transmission risk from an exposure. Research shows that the higher the viral load, the greater the risk. Viral load tests detect the amount of HIV in the blood of someone living with HIV and have shown that HIV treatment can reduce the level of the virus in the blood to undetectable levels (it should be noted that the virus is still present — the tests just can’t detect it). Viral load tests in Canada cannot detect HIV if there are fewer than 40 copies per millilitre. Given that antiretroviral therapy can also reduce HIV in the vaginal fluid, seminal fluid and/or rectal fluids, it can reduce the chance of transmitting HIV through sex.

In a landmark randomized controlled trial known as HPTN 052, treatment reduced the risk of HIV transmission among heterosexual serodiscordant couples (where one partner is HIV positive and the other is HIV negative) by 96%. In this study, the couples were mostly having vaginal sex and were provided with additional services that helped maximize the effectiveness of treatment, including ongoing adherence and prevention counselling, free condoms, viral load testing, and sexually transmitted infection testing and treatment. It is hard to know how much treatment will reduce the risk of HIV transmission in the “real world” where these additional services may not be available. Until recently, it was also unclear how much the results from HPTN 052 applied to populations that mostly have anal sex, such as some men who have sex with men. However, in March 2014, results from a preliminary analysis of an ongoing study (known as the PARTNER study) provided the first direct evidence that treatment can also significantly reduce the risk of HIV transmission through anal sex.

Although transmission risk was greatly reduced in the HPTN 052 study, there is a general consensus that HIV transmission is still possible when the viral load is undetectable, because treatment does not eliminate the virus from the body and even when the viral load is undetectable there may still be virus in the bodily fluids that can transmit HIV. There is research showing that HIV can sometimes be detected (although at lowered levels than in people who are not on treatment) in the genital and rectal fluids of some people who have an undetectable viral load in the blood. This may increase the risk of HIV transmission, although it is unclear by how much. The presence of a sexually transmitted infection in someone living with HIV can also increase the amount of virus in the genital and rectal fluids (but not necessarily in the blood). This may also increase the risk of HIV transmission.

The prevention benefits of treatment in individuals may translate to a reduction of HIV transmissions at a population level. The idea is that if enough people living with HIV are on successful treatment, the average amount of the virus circulating in the community (also known as community viral load) should be reduced. This reduction in average community viral load may result in fewer transmissions. Evidence suggests that treatment may be having a prevention impact in heterosexual populations in low-to-middle-income countries. Evidence also suggests that treatment may be having an impact on prevention in populations that use injecting drugs. However, “treatment as prevention” does not appear to be happening among many populations of gay men and other men who have sex with men. In most high-income countries, HIV incidence among men who have sex with men is remaining stable or continuing to increase despite increases in treatment coverage and decreases in community viral load. However, the evidence we have so far is observational and thus should be viewed cautiously because of the limitations of this type of research.

There are several barriers that prevent people living with HIV from being on successful treatment. The series of steps and services that an HIV-positive person must be engaged in to be on successful treatment (HIV testing, linkage to care, retention in care, initiation of treatment, treatment adherence) is also known as the HIV treatment cascade. The concept of an HIV treatment cascade has emerged as a way to identify gaps in this continuum of services.

These gaps mean that the proportion of people living with HIV who are on treatment and have an undetectable viral load is quite low in some areas. For example, it is estimated that only 19% to 28% of people living with HIV in the United States have an undetectable viral load. There are currently no official estimates for Canada; however, preliminary data suggest numbers in Canada may be similar to those in the United States.

Increasing the proportion of people living with HIV who have an undetectable viral load – and maximizing the prevention benefits of treatment – will require the development of interventions to:

  • increase the number of people who know they are HIV positive through HIV testing
  • increase the number of people who are linked to care after HIV diagnosis
  • ensure that people are supported to remain in care after being linked
  • improve access to antiretroviral therapy for people who are in care
  • ensure that people are supported and counselled to determine when they are ready and eligible to start treatment

In Canada, there are several small- and large-scale initiatives to improve engagement of people living with HIV in the HIV treatment cascade (such as the STOP HIV/AIDS Project in British Columbia). These have the potential to both improve health and reduce HIV transmission. However, excitement about the potential for treatment to prevent HIV transmission has led to concerns that there will be pressure on people to get tested, enter care and start treatment before they are ready. As these initiatives move forward, it is important to ensure that HIV-positive people are ready to begin the treatment cascade and that they have a full understanding of the potential risks and benefits.

A particular concern is that people living with HIV will be offered antiretroviral therapy before it is medically warranted, solely for the population’s benefit for HIV prevention. Starting individuals on treatment earlier than medically necessary may potentially increase the likelihood of poor adherence, virological failure, mortality, side effects and drug resistance. However, more and more research is showing that earlier initiation of HIV treatment is beneficial for people living with HIV, on the basis of clinical outcomes and the theory that chronic HIV inflammation may be damaging to the body over the long term.

The European AIDS Treatment Group along with NAM have developed an international community consensus statement endorsing the use of treatment as prevention which addresses many of these concerns.

Although treatment may have an important role to play in HIV prevention, it should be considered as one part of a comprehensive approach to HIV prevention.


Treating HIV to Prevent HIV Transmission

HIV viral load, HIV treatment and sexual HIV transmission – CATIE fact sheet

Insight into HIV transmission risk when the viral load is undetectable and no condom is usedCATIE News

Treatment and viral load: what do we know about their effect on HIV transmission?Prevention in Focus

Treatment as prevention: do the individual prevention benefits translate to the population level?Prevention in Focus

Expert Consensus Viral Load and Risk of HIV Transmission: Summary – Institut national de santé publique du Québec

Antiretroviral Treatment as Prevention (TasP) of HIV and TB – World Health Organization (WHO)


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