HIV diagnoses in British Columbia, Canada: a population-based study.

ssociation of highly active antiretroviral therapy coverage, population viral load, and yearly new HIV diagnoses in British Columbia, Canada: a population-based study.

Results of cohort studies and mathematical models have suggested that increased coverage with highly active antiretroviral therapy could reduce HIV transmission. Montaner and colleagues aimed to estimate the association between plasma HIV-1 viral load, antiretroviral therapy coverage, and number of new cases of HIV in the population of a Canadian province. They undertook a population-based study of antiretroviral therapy coverage and HIV transmission in British Columbia, Canada. Data for number of HIV tests done and new HIV diagnoses were obtained from the British Columbia Centre for Disease Control. Data for viral load, CD4 cell count, and antiretroviral therapy use were extracted from the British Columbia Centre for Excellence in HIV/AIDS population-based registries. They modelled trends of new HIV-positive tests and number of individuals on antiretroviral therapy using generalised additive models. Poisson log-linear regression models were used to estimate the association between new HIV diagnoses and viral load, year, and number of individuals on antiretroviral therapy. Between 1996 and 2009, the number of individuals actively receiving antiretroviral therapy increased from 837 to 5413 (547% increase; p=0.002), and the number of new HIV diagnoses fell from 702 to 338 per year (52% decrease; p=0.001). The overall correlation between number of individuals on antiretroviral therapy and number of individuals newly testing positive for HIV per year was -0.89 (p<0.0001).>For every 100 additional individuals on antiretroviral therapy, the number of new HIV cases decreased by a factor of 0.97 (95% CI 0.96-0.98), and per 1 log (10) decrease in viral load, the number of new HIV cases decreased by a factor of 0.86 (0.75-0.98). The study has shown a strong population-level association between increasing antiretroviral therapy coverage, decreased viral load, and decreased number of new HIV diagnoses per year. These results support the proposed secondary benefit of antiretroviral therapy used within existing medical guidelines to reduce HIV transmission.

Editors’ note: This publication has stimulated discussion about its premise, i.e. that community viral load is a key driving force for HIV transmission and that it can be reduced through antiretroviral treatment scale-up. Ecological studies are useful to generate hypotheses but cannot prove causality. In this case, rates of syphilis, gonorrhoea, and genital chlamydia increased steadily between 1996 and 2008 suggesting that safer sex practices did not account for the decline in new HIV diagnoses. For those on antiretroviral therapy, the proportion of non-injecting drug users with viral loads lower than 50 copies increased by 42% from 2004 to 2009 whereas this increase was much more marked among drug users (an increase of 86% over the same period). From 1999 to 2009, there was a 50% reduction in new diagnoses per year in people with a drug injecting history while the number of new positive tests remained stable in individuals with no history of injecting drug use. What this suggests is that it may be the combination of effective HIV prevention and antiretroviral treatment in the drug injecting community that is at the heart of most of the drop in new HIV diagnoses from 702 to 338 cases per year – and not antiretroviral treatment scale-up alone.