A big risk factor for spreading HIV and AIDS is use of injection drugs. Estimates suggest 5 to 10% of HIV infections worldwide are because of injection drug use.
In their paper, the researchers also note that:
"HIV/AIDS account for nearly a fifth of the burden of disease among people who use illicit drugs, and increases in HIV incidence have recently been reported among people who inject drugs in several different countries across geographical regions."
Addicts are most often prescribed methadone and buprenorphine, frequently as opiate substitutes.
Co-author Julie Bruneau, from the CHUM Research Centre (CRCHUM) and the Department of Family Medicine at the University of Montreal, says in a statement:
"There is good evidence to suggest that opiate substitution therapies (OST) reduce drug-related mortality, morbidity and some of the injection risk behaviors among PWID [people who inject drugs]."
"However, to date there has been no quantitative estimate of the effect of OST in relation to HIV transmission," she adds, explaining that their findings are important because "increases in HIV incidence have been reported among PWID in a number of countries in recent years, where opiate substitution therapies are illegal or severely restricted".
The researchers carried out a meta-analysis of several published and unpublished studies from Austria, Canada, China, Italy, the Netherlands, Puerto Rico, Thailand the UK and the US that had looked predominantly at men aged from 26 to 39 years.
The nine studies furnished an overall total of 23,608 person-years of follow-up and 819 incidences of HIV infection.
Pooling the results, the researchers found opiate substitution therapies were linked to a 54% fall in risk of HIV infection among people who inject drugs.
They couldn't calculate an "absolute reduction risk" for HIV infection because the studies weren't similar enough to allow it: for instance there were different background rates of HIV infection. Another reason was not all the studies reported adjustments in treatment to take into account things that might influence the link with opiate substitution therapies.
However, further analyses show the link to be strong and consistent, and there was little evidence that the longer the treatment the greater the benefit.
Bruneau says the findings support the use of opiate substitution therapies.
She says they show these therapies reduce HIV transmission in people who inject drugs, not only in countries where there is a high rate of HIV, but also in Quebec, which has recently seen a rise, particularly among young people, of intravenous use of illicit opiates, and where there are problems with accessing opiate substitution therapies.
Written by Catharine Paddock PhD