The absence of Canada's prime minister from the 16th International AIDS Conference in Toronto is drawing criticism from organizers.

The conference’s Canadian co-chairman, Dr. Mark Wainberg, finds it unacceptable Stephen Harper isn't among the 24,000 gathered for the event.

"We are dismayed that the prime minister of Canada, Mr. Stephen Harper, is not here this evening," Dr. Mark Wainberg said at the Rogers Centre on Sunday.

"Mr. Harper, the role of prime minister includes the responsibility to show leadership on the world stage. Your absence sends a message that you do not regard HIV/AIDS as a critical priority and clearly all of us here tonight disagree with you,” Wainberg said.

Canada's health minister defended the prime minister's absence, saying it doesn't mean a lack of commitment in the fight against AIDS.

Tony Clement said the federal government has adequate representation at the international conference and it is committed to helping people around the world through an access-to-medicine program.

No more rhetoric

"We don't need more rhetoric and more people saying 'Do this one thing and everything will be fine.' We actually need results," he said.

Those in attendance included philanthropists Bill and Melinda Gates, who gave the keynote speech on the conference's opening night. Bill Gates urged scientists to accelerate research on drugs that prevent the acquisition of HIV by women.

"We could revolutionize the fight against AIDS," he said.

Melinda Gates echoed her husband's comments earlier at a news conference, saying that microbicides will be an effective way of quelling the growth of HIV and AIDS.

"You have to put the power in the hands of women — that is going to be the way to change this epidemic," she said.

The conference began Sunday morning with a march through the streets that included blues singer Alicia Keys, Stephen Lewis, the UN secretary general's special envoy on AIDS in Africa, and 100 grandmothers from 13 African countries who were forced to raise their grandchildren after their children died of AIDS.

There are an estimated 58,000 people infected with HIV/AIDS in Canada alone. Of those, the Public Health Agency of Canada has estimated that 15,000 — or slightly more than 25 per cent — did not know they were infected.

This is the third time the conference has been held in Canada. It was held in Montreal in 1989 and in Vancouver in 1996.