July 19, 2010 -- New HIV diagnoses dropped by more than half since the introduction of highly active antiretroviral therapy (HAART) for HIV-infected patients, a Canadian study shows, suggesting that the treatment was effective at reducing viral load.

The study, based on HIV infections treated in the Canadian province of British Columbia -- showed that from 1996 to 2009, for every 100 patients placed on HAART, new HIV diagnoses decreased by 3%. Specifically, the researchers found that:

HAART use increased overall by 547% between 1996 and 2009;

During this period, new HIV diagnoses fell overall by 52%;

Also during this period, rates of sexually transmitted infections (such as chlamydia, gonorrhea, and syphilis) increased, suggesting that the decrease seen in new HIV diagnoses was not related to a decrease in risky sexual behavior.

The study was led by Julio Montaner, MD, director of the British Columbia Centre for Excellence in HIV/AIDS in Vancouver. The results will be presented this week at the International AIDS Society conference in Vienna, Austria, and were published on The Lancet’s web site.

“Our results show a strong and significant association between increased HAART coverage, reduced community viral load, and decreased number of new HIV diagnoses per year in the population of a Canadian province,” the authors say.