Open Access Highly Accessed Research article

Regional differences in rates of HIV-1 viral load monitoring in Canada: Insights and implications for antiretroviral care in high income countries

Janet M Raboud12*, Mona R Loutfy3456, DeSheng Su2, Ahmed M Bayoumi3578, Marina B Klein9, Curtis Cooper10, Nima Machouf11, Sean Rourke121337, Sharon Walmsley23, Anita Rachlis143, P Richard Harrigan1516, Marek Smieja17, Christos Tsoukas9, Julio SG Montaner1516, Robert S Hogg1618 and the CANOC Collaboration

Author Affiliations

1 Dalla Lana School of Public Health, University of Toronto, Toronto, Canada

2 Division of Infectious Disease, University Health Network, Toronto, Canada

3 Department of Medicine, University of Toronto, Toronto, Canada

4 Women's College Research Institute, Women's College Hospital, Toronto, Canada

5 Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada

6 Maple Leaf Medical Clinic, Toronto, Canada

7 Centre for Research on Inner City Health, The Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Canada

8 Division of General Internal Medicine, St. Michael's Hospital, Toronto, Canada

9 Department of Medicine, McGill University Health Centre, Montreal, Canada

10 University of Ottawa, Ottawa, Canada

11 Clinique m├ędicale l'Actuel, Montreal, Canada

12 Department of Psychiatry, University of Toronto, Toronto, Canada

13 Ontario HIV Treatment Network, Toronto, Canada

14 Division of Infectious Disease, Sunnybrook Health Sciences Centre, Toronto, Canada

15 Faculty of Medicine, University of British Columbia, Vancouver, Canada

16 The British Columbia Centre for Excellence in HIV/AIDS, Vancouver, Canada

17 Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Canada

18 Faculty of Health Sciences, Simon Fraser University, Vancouver, Canada

For all author emails, please log on.

BMC Infectious Diseases 2010, 10:40  doi:10.1186/1471-2334-10-40

Published: 25 February 2010



Viral load (VL) monitoring is an essential component of the care of HIV positive individuals. Rates of VL monitoring have been shown to vary by HIV risk factor and clinical characteristics. The objective of this study was to determine whether there are differences among regions in Canada in the rates of VL testing of HIV-positive individuals on combination antiretroviral therapy (cART), where the testing is available without financial barriers under the coverage of provincial health insurance programs.


The Canadian Observational Cohort (CANOC) is a collaboration of nine Canadian cohorts of HIV-positive individuals who initiated cART after January 1, 2000. The study included participants with at least one year of follow-up. Generalized Estimating Equation (GEE) regression models were used to determine the effect of geographic region on (1) the occurrence of an interval of 9 months or more between two consecutive recorded VL tests and (2) the number of days between VL tests, after adjusting for demographic and clinical covariates. Overall and regional annual rates of VL testing were also reported.


3,648 individuals were included in the analysis with a median follow-up of 42.9 months and a median of 15 VL tests. In multivariable GEE logistic regression models, gaps in VL testing >9 months were more likely in Quebec (Odds Ratio (OR) = 1.72, p < 0.0001) and Ontario (OR = 1.78, p < 0.0001) than in British Columbia and among injection drug users (OR = 1.68, p < 0.0001) and were less likely among older individuals (OR = 0.77 per 10 years, p < 0.0001), among men having sex with men (OR = 0.62, p < 0.0001), within the first year of cART (OR = 0.15, p < 0.0001), among individuals on cART at the time of the blood draw (OR = 0.34, p < 0.0001) and among individuals with VL < 50 copies/ml at the previous visit (OR = 0.56, p < .0001).


Significant variation in rates of VL testing and the probability of a significant gap in testing were related to geographic region, HIV risk factor, age, year of cART initiation, type of cART regimen, being in the first year of cART, AIDS-defining illness and whether or not the previous VL was below the limit of detection.