Drug-resistant TB is found by growing bacterium in a dish containing TB drugs; if the bacteria grow, they are resistant

WHO/TDR/Crump

An outbreak of 'extreme drug-resistant tuberculosis' in South Africa's province of Kwazula Natal is highlighting the urgent need for new drugs.

Known as XDR TB, the strain is virtually untreatable.

An emergency conference held last week in Johannesburg, South Africa, heard that almost all the 120 people known to have contracted the strain have died.

Neither the standard drugs nor at least three of the six classes of backup drugs are effective against the strain.

This is the first outbreak of XDR TB which, although present in several countries, has until now only caused isolated cases. The World Health Organization warns that many more people could be infected.

All those infected so far in South Africa also have HIV, so have weakened immune systems. This could mean that the strain is not virulent enough to make healthy people ill, but it could still spread quickly in a population with high levels of HIV.