Global alert over drug-resistant TB strains

World officials on Tuesday night put out an unprecedented warning that deadly new strains of tuberculosis (TB), virtually untreatable using the drugs currently available, appear to be spreading across the globe.

The new strains are known as extreme drug-resistant TB, or XDR-TB. They have been identified and have killed people in several countries, including the US and eastern Europe, and they have recently been found in Africa, where they could swiftly put an end to all hope of containing the AIDS pandemic through treatment.

Paul Nunn, who heads the WHO's TB resistance team, said the situation was very serious. There are 9 million cases of TB in the world and the WHO estimates that 2 percent of them -- or 180,000 -- could be XDR-TB.

"This is raising the spectre of something that we have been worried might happen for a decade -- the possibility of virtually untreatable TB," Nunn said.

Even in the US, which has the best medicines available, a third of those who have been diagnosed with XDR-TB have died. In March, the Centers for Disease Control in the US registered that there had been 64 cases of XDR-TB; 21 of those ended in death.

Significant of cases have been confirmed in Latvia and Russia, but in many parts of the world, XDR-TB could be rife but unrecognized. One of the reasons the WHO is concerned is that tuberculosis spreads easily in confined places, such as aircraft. Multi-drug resistant TB strains -- those that are resistant to the two basic, first-line drugs used to treat the disease -- have spread everywhere, including to the UK. Multi-drug resistant TB is increasingly common and is difficult and expensive to treat. The patient must be given four out of the six existing second-line drugs.

But the XDR-TB strains now appearing are a medical nightmare because at least three out of those six second-line drugs have no effect. There are no third-line drugs.

The specter of a new untreatable plague has concentrated minds because of the identification of a cluster of cases in KwaZulu-Natal, in South Africa. Scientists ran tests on people with tuberculosis in a rural part of the region. They studied 544 patients and found that 221 had TB strains against which the two common drugs, rifampicin and isoniazid, had no effect.

Finding a high rate of multi-drug resistant TB was serious enough. But they also discovered that 53 of the patients had XDR-TB -- and 52 of them died within an average of 25 days.

All the XDR-TB patients who could be tested were found to be HIV positive. Anybody with the virus becomes very susceptible to all types of infection. Tuberculosis is a major killer of people with AIDS.