GENEVA -- A new test to screen for drug-resistant tuberculosis will greatly help the fight against the disease in developing countries, the World Health Organization (WHO) said on Monday.

The test, which involves examining DNA in the saliva of sick people, will provide a diagnosis within two days instead of the usual two to three months.

"It is a major revolution in TB control," the director of the WHO's TB campaign Mario Raviglione said at a news conference in Geneva.

In developing countries most TB patients are tested for multidrug-resistant tuberculosis (MDR-TB) only after they fail to respond to standard treatments.

Patients have to wait months for the results before they can receive life-saving treatment. During this period they can spread the disease to those around them. Often they die before the results are known.

Close to half a million people around the world suffer from some form of MDR-TB, which kills around 130,000 people a year.

The WHO estimates that only two percent of drug-resistant cases worldwide are diagnosed and treated appropriately, mainly because of the poor state of health services in many countries.

The new tests, funded with $26.1 million (?16.5 million) from the global health initiative UNITAID, should increase that proportion to at least 15 percent over the next four years.