The World Health Organization says it is concerned about the emergence of a new drug-resistant strain of tuberculosis (TB).

International health experts are set to meet Thursday and Friday in Johannesburg to discuss stronger preventative measures against this deadly form of the disease.

The WHO says the strain, known as XDR-TB, is virtually untreatable and has an alarmingly high mortality rate.

It says one recent outbreak in the Kwazlul-Natal province of South Africa killed 52 of 53 patients infected.  Most of the victims were HIV-positive.

Health officials warn that people infected with HIV are particularly susceptible to XDR-TB because of their already weakened immune systems.

In its press release Tuesday, WHO officials said drug-resistant tuberculosis could have a severe impact on mortality in Africa, given the underlying HIV epidemic.

It noted that the strain has been found in all regions of the world, most frequently in the countries of the former Soviet Union and in Asia.

Some information for this report was provided by AP.