The cascade of HIV care in British Columbia, Canada, 1996-2011: a population-based retrospective cohort study

Abstract

Background: The cascade of HIV care has become a focal point for implementation efforts to maximise the individual and public health benefits of antiretroviral therapy. We aimed to characterise longitudinal changes in engagement with the cascade of HIV care in British Columbia, Canada, from 1996 to 2011.

Methods: We used estimates of provincial HIV prevalence from the Public Health Agency of Canada and linked provincial population-level data to define, longitudinally, the numbers of individuals in each of the eight stages of the cascade of HIV care (HIV infected, diagnosed, linked to HIV care, retained in HIV care, highly active antiretroviral therapy (HAART) indicated, on HAART, adherent to HAART, and virologically suppressed) in British Columbia from 1996 to 2011. We used sensitivity analyses to determine the sensitivity of cascade-stage counts to variations in their definitions.

Findings: 13,140 people were classified as diagnosed with HIV/AIDS in British Columbia during the study period. We noted substantial improvements over time in the proportions of individuals at each stage of the cascade of care. Based on prevalence estimates, the proportion of unidentified HIV-positive individuals decreased from 49·0% (estimated range 36·2-57·5%) in 1996 to 29·0% (11·6-40·7%) in 2011, and the proportion of HIV-positive people with viral suppression reached 34·6% (29·0-43·1%) in 2011.

Interpretation: Careful mapping of the cascade of care is crucial to understanding what further efforts are needed to maximise the beneficial effects of available interventions and so inform efforts to contain the spread of HIV/AIDS.

Funding: British Columbia Ministry of Health, US National Institute on Drug Abuse (National Institutes of Health).

Figure 1. Estimated annual HIV prevalence and number of individuals diagnosed

Prevalence estimates are based on unpublished data from the Public Health Agency of Canada (Archibald C, Public Health Agency of Canada, personal communication).

Figure 2. The cascade of HIV care

HAART=highly active antiretroviral therapy.

Figure 3. Changes in leakage from the cascade of HIV care

Shaded region in (A) represents HIV prevalence range estimates from the Public Health Agency of Canada (Archibald C, Public Health Agency of Canada, personal communication). HAART=highly active antiretroviral therapy.

Figure 4. Sensitivity analyses for cascade-stage definitions

Viral suppression thresholds: <500 copies per mL for 1996, <400 copies per mL for 1997–98, and <50 copies per mL for 1999–2011. HAART=highly active antiretroviral therapy. MSP=medical services plan. *Takes into account all diagnosed individuals in the numerator of the estimated proportion, including those who did not meet the baseline thresholds for adherence, being on HAART, HAART indicated, or retained in or linked to care.

Figure 5. Cascade of HIV care, including estimates of HIV prevalence and ranges from sensitivity analyses

Prevalence estimates are based on unpublished data from the Public Health Agency of Canada (Archibald C, Public Health Agency of Canada, personal communication). Error bars represent plausible intervals from sensitivity analyses of cascade-stage definitions. HAART=highly active antiretroviral therapy.

Figure 6. Aggregate HIV-1-RNA concentrations in HIV-positive individuals

Data represent the highest plasma viral load measurement for each individual who received a plasma viral load test in each calendar year. *Viral suppression thresholds: <500 copies per mL for 1996, <400 copies per mL for 1997–98, and <50 copies per mL for 1999–2011.