World TB Day this year focuses on eradicating the disease, which kills more than two million people annually. But, health officials underscore how difficult a task that is, because of widespread resistance to drugs designed to treat tuberculosis. Experimental drugs, that researchers hope will usher in a new era of TB therapy are under development.

The U.S. Centers for Disease Control in Atlanta has compiled what it says is the first global survey of highly drug-resistant tuberculosis, which kills 5,000 to 8,000 people every day.

The survey, conducted by laboratories on all six continents, found growing resistance to TB drugs worldwide, a development the CDC says means some patients are "virtually untreatable" with existing drugs.

The CDC calls tuberculosis that is resistant to old and new antibiotic drugs "extensively drug-resistant TB," or XDR.

But researchers at Albert Einstein College of Medicine of Yeshiva University in New York are experimenting with compounds that appear to be up to 10 times more potent than existing tuberculosis drugs.

Researcher William Jacobs says the drugs appear to work well against TB because of the comprehensive nature of the attack.

"You know, the problem is, if you just hit a single target, you are likely to get drug resistance," said William Jacobs. "That is less likely to happen, if you hit multiple targets. And what these new compounds do is, they target three different pathways that are absolutely essential for M. [mycobacterium] tuberculosis to grow and persist."

Meanwhile, to coincide with World TB Day, a foundation backed by the Microsoft founder Bill Gates and his wife Melinda and set up to develop a tuberculosis vaccine opened its first factory in the U.S. state of Maryland on Thursday.

The Global TB Vaccine Foundation wants to develop a replacement for the BCG (Bacille Calmette-Guerin) vaccine, which seems to work in young children, but is generally found to be ineffective in adults.