The world is on the cusp of an explosion of drug-resistant tuberculosis cases that could deluge hospitals and leave physicians fighting a nearly untreatable malady with little help from modern drugs, global experts said Wednesday.

"The situation is already alarming, and poised to grow much worse very quickly," said Dr. Margaret Chan, director-general of the World Health Organization.

With Bill Gates at her side, Chan urged health officials from 27 countries at a three-day forum on drug-resistant TB to recognize the warning signs of what looms ahead, saying that traditional drugs are useless against some strains of tuberculosis and health care costs for treating those strains can be 100 to 200 times more than for regular tuberculosis.

"This is a situation set to spiral out of control. Call it what you may: a time bomb or a powder keg. Any way you look at it, this is a potentially explosive situation," Chan warned.

Gates, the software magnate turned philanthropist, said scientific overconfidence has led to a lack of innovation and urgency in fighting tuberculosis, which affects nine million people each year, killing nearly two million of them.

"The most commonly used diagnostic test is today more than 125 years old," Gates said. "The vaccine was developed more than 80 years ago, and drugs have not changed in 50 years.'

Tuberculosis is a highly contagious bacterial infection that attacks the lungs, and can affect other organs. Coughing, sneezing and even talking can spread the bacteria. If untreated, a person with TB can infect 10 to 15 other people in a year.

Once thought conquered in developed countries, virulent forms of tuberculosis are again on the march, caused often by improper use of drugs and poorly managed treatment regimes. It remains largely a disease of poverty.

Chan said traditional treatment often leaves the patient wishing to end the medicine.

"Instead of taking two to four pills, one has to take 13 pills. Put yourself in the position of the patient. Thirteen pills are not 13 candies," Chan said, noting that courses of treatment can last four to six months and patients don't like the hassle of taking the pills for so long.

Outbreaks of multi-drug resistant strains of tuberculosis are highest in India, China, Russia, South Africa and Bangladesh. Scientists now see even worse strains they label extensively drug-resistant TB that can be treated neither with the two principle anti-TB drugs nor with more expensive second-line drugs.

In early 2007, 20 countries reported cases of the more fatal TB. By the end of 2008, 54 countries reported the malady.

Jorge Sampaio, the U.N. secretary-general's special envoy to halt TB, called the extensively drug-resistant strain "a very deadly and devastating epidemic."

Later in the day, Gates offered a grant of $33 million to China's ministry of health to finance what he called an innovative pilot program for TB prevention that could be used in other nations. The program uses new systems to reduce pill intake, offers incentives for doctors to monitor TB, and funds development of new diagnostic tests.

China has about 1.5 million cases of TB each year. Under the pilot program, TB patients will get medicine kits with built-in reminder alarms as well as receive cell phone text messages reminding them to take their medicines.

Gates said his Bill & Melinda Gates Foundation is financing research on a new TB vaccine and that "it'll be about five to six years from now before we could have a completely new vaccine."