Zarir Udwadia, a tuberculosis (TB) doctor at the Hinduja National Hospital in Mumbai, said compared to classifications used by the government and the World Health Organization (WHO) to describe malicious strains - multi-drug resistant (MDR) and extensively drug-resistant (XDR) TB - the patients diagnosed at his hospital were different.

"It is an untreatable form of TB in the sense that there are no available first- and second-line drugs for it in the world," he said in a telephone interview.

If a first six-month course of drugs fails to work, so-called second-line drugs are used for longer periods in attempts to cure the TB infection.

"XDR is easier to treat ... there are three to four second-line drugs still available which you can treat these patients with, but (for) our patients there is none."

He said the cases highlighted the need for India to pay more attention to treating patients with severe forms of TB, which the WHO said numbered around 110,000 in 2006, a figure Udwadia said was a "considerable underestimate."

But India's government said on Tuesday the laboratory at Hinduja hospital was not accredited for some of the tests that Udwadia's team carried out and questioned the term "totally drug resistant TB."

"The term ... is neither recognized by the WHO nor by the Revised National Tuberculosis Control Programme," it said in a statement. Such cases can be managed by national XDR-TB treatment guidelines, according to the WHO.

Udwadia and colleagues cultured TB bacteria taken from the patients, exposed them to all first- and second-line TB drugs and found them all powerless. They also performed genetic tests on the samples.

"We confirmed that whether we used traditional culture or genetic (tests), we came up with the same resistance pattern. These patients were already exposed to these drugs and ... they did not work in them," Udwadia said.

Udwadia said patients who contract drug-resistant TB face a problem as many private doctors are untrained in diagnosing and managing these more severe forms.

"They will get more and more malnourished, eventually they die without any available drug," Udwadia said when asked what would happen to those with untreatable forms of TB.

The first four of Udwadia's patients with this form of TB were described in a letter that he and colleagues published in the journal Clinical Infectious Diseases in December 2011.

According to medical literature, cases of such untreatable TB were first reported in 2007 in Europe. In 2009, 15 patients in Iran were reported to be resistant to all anti-TB drugs.

TB is caused by mycobacterium tuberculosis and destroys lung tissue, causing victims to cough up the bacterium, which then spreads through the air and can be inhaled by others.

An ancient, long-neglected disease, the world has had no new vaccines or drugs to fight TB for decades even though it is still a leading killer. In 2010, 8.8 million new cases were reported, with 1.45 million deaths worldwide.

(Writing by Tan Ee Lyn; Editing by Ed Lane)

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