A newly identified strain of extremely drug-resistant tuberculosis leaves patients "virtually untreatable," officials with the World Health Organization warn.

On Thursday and Friday, tuberculosis experts will meet in South Africa to evaluate possible ways to deal with drug-resistant TB, especially in Africa.

Tuberculosis causes about 1.7 million deaths a year worldwide, but researchers are worried about the emergence of strains that are resistant to drugs.

Multidrug-resistant TB is already a concern because at least two of the main first-line drugs won't work against the strain.

Now, extensive drug-resistant TB or XDR-TB is emerging, in which the bacteria resist not only front-line drugs, but also three of the more than six classes of second-line drugs. While more potent, these medications have more serious side-effects, are more expensive and may need to be taken for as long as two years. 

On average, about one per cent of all strains are drug-resistant, and of those, between five and 15 per cent are extensively drug-resistant, said Dr. Anne Fanning, a professor emeritus at the University of Alberta's faculty of medicine.

Call for access to better treatments

"It is of grave concern if it is not appropriately addressed," Fanning told CBC Newsworld. "Drug resistance happens if treatment is not handled well. Good TB treatment in the first instance cures. Poor treatment creates drug resistance."

The problems arise mainly from poorly managed care of people infected with TB, for example when they are given poor-quality drugs for the wrong period of time, WHO said.

Of the nine million cases of TB worldwide, about half the patients don't have access to proper treatments, Fanning said in calling for improved treatments and funding from donor countries such as Canada.

A survey of 18,000 TB samples by the U.S. Centers for Disease Control and WHO between November 2004 and November 2005 found XDR-TB in all regions of the world, including the United States.

The XDR-TB strains were found most frequently in the former Soviet Union and Asia. Cases are also on the rise in Africa.

"Given the underlying HIV epidemic, drug-resistant TB could have a severe impact on mortality in Africa and requires urgent preventative action," WHO said in a statement.

A cluster of XDR-TB cases among 53 HIV-positive patients in Kwazulu-Natal in South Africa showed an alarming mortality rate, with 52 dying within 25 days of their diagnosis in spite of receiving anti-retroviral drugs.