In the world of tuberculosis (TB) control, it is the worst-case scenario. Doctors in Mumbai, India, reported last month they are seeing a group of patients infected with what they called "totally drug-resistant" tuberculosis. Indian health officials are still investigating those cases, but untreatable strains of the bacterial respiratory disease have turned up before: in 15 patients in Iran in 2009 and in two patients in Italy in 2007.  Public health experts responding and there is new hope some for new weapons against a disease that is killing 5,000 people every day.

The World Health Organization (WHO) lists 69 countries that have reported what is officially called "extensively drug-resistant" tuberculosis (XDR-TB).  It's a form of the mycobacterium that, like the one reported in India, isn't killed by first- and second-line anti-TB injectable drugs. The WHO says at least 25,000 cases of XDR-TB are reported worldwide every year.

Dr. Margaret Chan, WHO's director-general, views the emergence of drug-resistant tuberculosis with alarm.

"Call it what you may, a time bomb or a powder keg. Any way you look at it, this is a potentially explosive situation," she said.

Officials say drug-resistant TB has been a growing problem in countries such as India and China because patients are frequently misdiagnosed and often receive inappropriate or inadequate treatment with antibiotics.  Misuse of these drugs increases the danger that the target pathogen will gradually develop resistance to them.

Dr. Neeraj Mistry, a public health physician, says surveys show that very few Indian doctors are actually treating TB patients with the right drugs for the right length of time.

"The emergence of totally-resistant TB is a result of failed public health intervention strategies," said Mistry.  "When we deliver ineffective treatment regimens and when we don't have full adherence and compliance to treatment, it enables the emergence of resistance within the individual."

Experts say that with the current arsenal of drugs failing to hold the line against TB, the need for new drugs and compounds has become more urgent.  Preventing TB through vaccination is one promising strategy.

"The ideal would be to develop a vaccine that works in all age groups. Everyone from newborn through the elderly," noted Dr. Ann Ginsberg of the Aeras Global TB Vaccine Foundation.

Ginsberg and her colleagues are running clinical trials on two TB vaccines they hope will provide long-lasting immunity to TB and stop transmission of the disease. If all goes as planned, she says, the vaccine will be ready by 2020.

"The clinical development program for a TB vaccine is a very long process, and it's long because, first of all, it's the nature of the disease itself - people get infected with TB and often don't get sick for years," added Ginsberg.  "So when you do a vaccine trial, you have to vaccinate people and watch them for years to see whether or not they will get the TB.  So that makes these clinical trials very long."

While the world waits for that TB vaccine, the WHO says a new line of TB drugs - fortified with a new class of potent anti-mycobacterial agents - could be available by the end of this year or early next.