This is the worrying growth in the resistance of infectious diseases to conventional medicines, largely caused by the world's over-use of cheap antibiotics.
Potentially fatal diseases like tuberculosis are developing resistance to the most commonly-used drugs, but the big pharmaceutical companies have little incentive to spend billions on finding replacements if poorer countries cannot afford to pay for them.
This is the big healthcare economics conundrum facing the world.
"If we don't find a solution to this enormous challenge by 2050, 10 million people a year could be dying from it", economist Jim O'Neill told the BBC World Service's In the Balance programme.
Last year, Mr O'Neill, former chief economist at investment bank Goldman Sachs, was given the unusual role of heading up a government-backed commission looking into antimicrobial resistance.
The term covers not only those drugs used to treat bacterial infections, but also those used to treat other microbes, such as parasites, viruses, and fungi.
Hundreds of thousands more people are dying each year from infectious diseases that used to be easily treatable, health experts believe.
Bacteria become resistant to antibiotics over time, but overuse of the drugs accelerates the process. The WHO reports seeing growing resistance to "front line drugs" in most parts of the world.
Mr O'Neill's commission has estimated that these extra deaths could cost the global economy $100bn (Â£65bn; â‚¬89bn).
But what should "big pharma", governments and health professionals be doing about it?
According to Mr O'Neill, this is as much a problem of economics as healthcare.
"There's a major demand problem and there's a major supply problem," he told the BBC.
On the the supply side, pharmaceutical companies want to develop drugs that they can sell a lot of at high prices, he said. But in emerging economies, this is not affordable.
So pharma firms are reluctant to commit billions of dollars on research and development that might lead to new, more effective drugs, without being confident they will recoup costs and make a profit.
On the demand side, there's a pressing need for patients and doctors to realise that antibiotics "are not sweets," says Mr O'Neill. "We all think that they solve anything, but they don't, they cause resistance."
The Association of the British Pharmaceutical Industry (ABPI) recognises that more needs to be done to make sure that the right drugs are being prescribed appropriately.
Dr Virginia Acha, the ABPI's executive director of research medicine and innovation, also accepts that a change to the traditional drug development business model will be needed if this problem is to be addressed.
"You're going to need new [drugs] eventually, just because of the process of the way bacteria respond," says Ms Acha.
But the issue is not just about developing new drugs, she argues, it's also about having them readily available and at the right volumes.
She suggests new funding models could involve insurance-based schemes or collective investment from governments, pharma firms, research institutes and charities.
Mr O'Neill believes that developing 10 new key drugs over the next decade would cost about $25bn.
"It sounds a lot of money, but that is less than a third of a tenth of a percent of global GDP," he says."And it's less than the global pharma industry spends on buying back its own shares every year."
But he admits that "global taxpayer money" will be needed to keep the costs of the drugs low enough to be affordable for developing economies.
Meanwhile, in densely-populated countries like India that are particularly prone to multiple infectious diseases, antimicrobial resistance is taking an increasingly savage toll.
A high mortality rate in new-born babies in India is "attributable to bacterial infections", says Prof Vinod Paul, head of paediatrics at the All India Institute of Medical Sciences in Delhi. "Almost 200,000 babies are dying each year."
But using antibiotics risks triggering more microbial resistance, says Prof Paul.
"We are walking a tight-rope."
So what should governments be doing?
"Better infection prevention and control in healthcare settings; a focus and hygiene and sanitation; where appropriate, increasing vaccination uptake," says Dr Charles Penn, the World Health Organization (WHO) co-ordinator for antimicrobial resistance.
All of which would reduce the reliance on antibiotics, he argues. New drugs need to be available to all, but they should be used "wisely and appropriately" so that they remain effective for "as long as possible," he says.
Most experts agree that co-operation between the private and public sectors will be essential to prevent millions of additional fatalities over the coming decades.
There has to be an "international call to arms", concludes the ABPI's Virginia Acha.
The World Health Organization (WHO) calls it "one of the most serious global health threats of our time".