Background: Viral load (VL) monitoring is an essential component of the care of HIV positive individuals. Rates ofVL monitoring have been shown to vary by HIV risk factor and clinical characteristics. The objective of this studywas to determine whether there are differences among regions in Canada in the rates of VL testing of HIV-positiveindividuals on combination antiretroviral therapy (cART), where the testing is available without financial barriersunder the coverage of provincial health insurance programs.Methods: The Canadian Observational Cohort (CANOC) is a collaboration of nine Canadian cohorts of HIV-positiveindividuals who initiated cART after January 1, 2000. The study included participants with at least one year offollow-up. Generalized Estimating Equation (GEE) regression models were used to determine the effect ofgeographic region on (1) the occurrence of an interval of 9 months or more between two consecutive recordedVL 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.Results: 3,648 individuals were included in the analysis with a median follow-up of 42.9 months and a median of15 VL tests. In multivariable GEE logistic regression models, gaps in VL testing >9 months were more likely inQuebec (Odds Ratio (OR) = 1.72, p < 0.0001) and Ontario (OR = 1.78, p < 0.0001) than in British Columbia andamong injection drug users (OR = 1.68, p < 0.0001) and were less likely among older individuals (OR = 0.77 per10 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) andamong individuals with VL < 50 copies/ml at the previous visit (OR = 0.56, p < .0001).Conclusions: Significant variation in rates of VL testing and the probability of a significant gap in testing wererelated to geographic region, HIV risk factor, age, year of cART initiation, type of cART regimen, being in the firstyear of cART, AIDS-defining illness and whether or not the previous VL was below the limit of detection
