As the pleas to bolster - or at least maintain - funding for HIV-AIDS grow louder, so too are demands that the money be spent more wisely and efficiently.

"We can't get rid of this epidemic without more money and without profoundly changing what we do with it," Bill Clinton, the former U.S. president, told delegates at the 18th International AIDS Conference in Vienna.

He called on those involved in the fight against HIV-AIDS, from governments through to non-profits, to pull up their socks and ensure that every penny donated to the cause is spent wisely and efficiently.

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"Every dollar we waste today puts a life at risk," Mr. Clinton said.

At the same time, he insisted that global health, and HIV-AIDS in particular, is an "extraordinarily good economic investment with a high rate of return."

Mr. Clinton, who heads the William J. Clinton Foundation, urged donors, from individuals to governments, to not use the recession as an excuse to cut back.

But he also told activists at the conference that: "If we're going to make this case, they have to believe that we are doing our job faster, better and cheaper."

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Bill Gates, the former chairman of Microsoft Corp,. who is now co-chair of the Bill and Melinda Gates Foundation, delivered a similar message, saying economic turbulence has created a real challenge but the answer is not to despair, but to improve efficiency.

"This is a tough economic environment," he said. "There isn't enough money to simply spend our way out of this epidemic. If we keep spending our resources in exactly the same way we do today, we will fall further behind."

Mr. Gates used the example of antiretrovirals to make the case for the importance of efficiency. He noted that drug treatment costs for HIV-AIDS sufferers were as high as $10,000 (U.S.) but, with a determined effort that was brought down as low as $100 in developing countries. More than five million people are now on treatment.

However, it can cost up to $2,000 a year to deliver those drugs, though countries like Botswana and Nigeria have brought the delivery cost to around $250.

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"For the same amount of money we spend today, we could treat more than twice as many people," Mr. Gates said.

In 2009, spending on HIV-AIDS worldwide reached $15.6-billion (U.S.), according to UNAIDS. That is almost double the $7.9-billion spent in 2005.

However, financial fears have cast a pall over the International AIDS Conference because spending on HIV-AIDS actually stagnated between 2008 and 2009.

This is also a year that countries need to renew their pledges to the Global Fund for AIDS, Tuberculosis and Malaria, which provides the bulk of funding for AIDS prevention and treatment in the developing world.

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"2010 is a decisive year. We are very worried about replenishment," said Michel Kazatchkine, executive director of the Global Fund.

He said the fund needs between $17-billion and $20-billion to continue its work and failure to meet the target will have "devastating consequences. HIV, TB and malaria treatment would be denied to millions."

Canada pledged $143-million (U.S.) to the Global Fund in 2010 but has yet to make a commitment for the next three years.

A large group of protesters marched noisily through the conference Monday, chanting: "No retreat, tax and treat."

The groups, from around the world, were demanding governments not cut AIDS funding but also calling for new methods of raising money, such as the so-called Robin Hood tax and the airlines tax.

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The idea of a financial transaction tax was initially proposed in 1971 by Nobel Prize-winning economist James Tobin, but has been embraced in recent years by anti-poverty and AIDS activists. They want governments to impose taxes that would average about 0.05 per cent on transactions between financial institutions, and to use the proceeds to improve the health status of the world's poorest citizens.

Mr. Gates pooh-poohed the idea of the Robin Hood tax saying "I know a lot of experts who say it's not workable." But at the same time, he said the "airline tax is fantastic."

France has, for many years, levied a tax on airline tickets to fund development projects. The idea has been bolstered by online travel companies who now ask customers to make a voluntary $2 contribution with each purchase, money that goes to UNITAID, a United Nations agency that works in the field of AIDS, tuberculosis and malaria.

Mr. Clinton also heaped praise on the airline tax - voluntary or otherwise - saying that the best way to ensure that the HIV-AIDS gets adequate money is to "raise small amounts of money from a massive number osf people."