19 February 2014 

Gaps in British Columbia’s HIV treatment cascade

The introduction of antiretroviral treatment (ART, also known as highly active antiretroviral therapy or HAART) in 1996 was a significant moment in the response to HIV. Successful antiretroviral treatment can suppress HIV replication in the body and lower the viral load (amount of virus) in a person’s bodily fluids to undetectable levels. While research has long shown that a lower viral load can improve the health of a person living with HIV, more recent studies have demonstrated that it can also reduce the risk of HIV transmission.

As HIV treatment and prevention have converged, attention has turned to how well people living with HIV are being engaged in the continuum of services needed to achieve an undetectable viral load—including testing and diagnosis, care and support, and treatment. The concept of an HIV treatment cascade, or HIV care cascade, has emerged as a way to identify gaps in the continuum, which are preventing people from realizing the health and prevention benefits of antiretroviral treatment.

In the United States, it is estimated that only 19 to 28% of people living with HIV are on treatment and have an undetectable viral load, suggesting that there are significant gaps in the continuum of HIV services. However, less is known about the treatment cascade in Canada. As a result, researchers in British Columbia decided to characterize the cascade in their province, identify gaps and look at how engagement in the care cascade has changed since antiretroviral treatment first became available in 1996.

Building the cascade

The study investigators constructed a treatment cascade for each year from 1996 to 2011. The cascades show the sequence of steps needed to achieve an undetectable viral load and the proportion of individuals living with HIV who were engaged at each stage. The steps include diagnosis, linkage to care, retention in care, treatment eligibility, initiation of treatment, treatment adherence and virological suppression.

To collect the required information, a recently developed, advanced surveillance system linking data from several sources was used. Data sources included the Public Health Agency of Canada, BC Centre for Disease Control, British Columbia Centre for Excellence in HIV/AIDS and the provincial physician billing database.


Significant gaps were identified in the most recent cascade. Of the estimated 11,700 people living with HIV in 2011, only 4,054 (35%) are thought to have achieved an undetectable viral load. This means that 7,646 people (65%) did not have an undetectable viral load and were therefore not engaged in all of the steps in the cascade.

At each step along the continuum, people were lost.  Among the people living with HIV in BC in 2011:

  • 8,308 (71%) had been diagnosed with HIV
  • 7,801 (67%) had been linked to care
  • 6,688 (57%) had been retained in care
  • 6,224 (53%) were in care and eligible to receive ART
  • 5,975 (51%) had started ART
  • 4,054 (35%) had started ART and had an undetectable viral load

While several gaps were identified in the 2011 cascade, the study found that engagement in the cascade had improved significantly since 1996. For example:

  • The proportion of people living with HIV who had not been diagnosed decreased from 49% in 1996 to 29% in 2011.
  • The proportion of people living with HIV who were diagnosed but not linked to care or retained in care decreased from 42% in 1996 to 19% in 2011.
  • The proportion of people living with HIV who were on treatment but did not have an undetectable viral load decreased from 97% in 1996 to 32% in 2011.

As a result of improved engagement in several steps of the treatment cascade, the proportion of people living with HIV who had an undetectable viral load increased from 1% in 1996 to 17% in 2003 and 35% in 2011.


While the proportion of individuals living with HIV who were engaged in British Columbia’s cascade improved substantially between 1996 and 2011, this study found that a large number of people were still lost from the continuum at different stages.

This is the first comprehensive study of a treatment cascade in Canada. While this study only focused on British Columbia, it is likely that similar gaps in the cascade exist in other parts of the country. As a result, interventions are needed to improve services at every stage of the cascade—HIV testing and diagnosis, linkage to care, retention in care, access to treatment and adherence to treatment. Such efforts have the potential to improve the health of people living with HIV and reduce the number of new HIV infections.

The authors of the study concluded that “careful mapping of the cascade of care is crucial to improve our understanding of how to maximize the beneficial effects of available interventions and to inform efforts to contain the spread of HIV/AIDS.” Hopefully this study will lead to research on the treatment cascade in other parts of Canada. Such research will likely require the development of more advanced surveillance systems that are able to link information from different provincial/territorial data sources.

—James Wilton


The HIV treatment cascade – patching the leaks to improve HIV preventionPrevention in Focus

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


  1. Vital signs: HIV prevention through care and treatment—United States. MMWR Morbidity and Mortality Weekly Report. 2011 Dec 2;60(47):1618–23.
  2. Gardner EM, McLees MP, Steiner JF et al. 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 15;52(6):793–800.
  3.  Nosyk B, Montaner JSG, Colley G et al. The cascade of HIV care in British Columbia, Canada, 1996-2011: a population-based retrospective cohort study. Lancet Infectious Diseases. 2014 Jan;14(1):40–9.