Smoking crack cocaine daily adds to the risk of spreading HIV, a Canadian study published on Monday says, although researchers acknowledge they are not sure about the exact link.

The researchers, who studied the relationship between drug use and HIV in Vancouver's impoverished Downtown Eastside, one of Canada's most drug infested neighborhoods, said the findings show the need for new efforts, such as opening "safe inhalation rooms", to help drug addicts.

The nine-year study, published in the Canadian Medical Association Journal, also found that the number of addicts smoking crack cocaine on a daily basis in the neighborhood has increased steadily.

The Vancouver neighborhood's problems of drugs, poverty and homelessness are expected to attract substantial international media attention this winter, when the Pacific Coast city hosts the Winter Olympics.

Researchers said that when they began the study in 1996 they did not see evidence that smoking crack cocaine daily increased the risk of contracting HIV, the human immunodeficiency virus that causes AIDS.

But signs of risk association developed midway through the study and evidence increased over time, along with growth in the number of study participants who admitted to smoking crack, a solid variant of cocaine that is highly addictive.

Study participants who reported smoking crack on a daily basis were four times more likely to become infected with HIV than those who smoked it less often or not at all, according to the researchers.

The virus may be spread because addicts with mouth wounds share smoking pipes with HIV-infected users, but the researchers said they did not know for sure. Engaging in unprotected sex while on drug binges might also be a cause, they said.

The neighborhood has a higher rate of HIV infection and AIDS than anywhere else in Canada. By the end of the project nearly 40 percent of the study's participants smoked crack daily.

The link between the spread of HIV and injection drug use was already well known, but researcher Evan Wood of the British Columbia Centre for Excellence in HIV/AIDS acknowledged he was somewhat surprised that smoking crack also posed a risk.

The findings are evidence Canada should consider programs to treat crack smoking as a health problem rather than as a law enforcement problem, Wood said in an interview.

"The current approach simply isn't working," he said.

Among treatment ideas suggested by the research is the establishment of facilities at which drug users could smoke under medically supervised conditions with access to information that could help them fight their addictions.

Vancouver already has North America's only sanctioned facility for users of injection drugs - a project that has the support of local and provincial officials but which the federal Conservative government is trying to shut down.

An appeals court is expected to rule shortly on Ottawa's challenge of a lower court decision requiring it to allow the Insite supervised injection facility to remain open.