TB affects mostly adults in their productive years; more than 50% of TB deaths occur in Asia Credit: Elena Korenbaum

Like something out of a horror movie, a lethal strain of tuberculosis blazed in 2005 across Tugela Ferry, a small village in South Africa, striking down nearly everyone it touched.

The strain, dubbed XDR for extensively drug-resistant, doesn't respond to known TB drugs and killed 52 of 53 infected individuals—all those tested found to be HIV-positive—and all of them within weeks of diagnosis (Lancet 368, 1575–1580; 2006).

Even among experts, the strain was cause for alarm. “The epidemic situation is very unusual, patients dying so rapidly,” says Salim Karim, director of Caprisa, a Durban-based consortium of AIDS and TB researchers.

What is less unusual, however, isn't more reassuring.

“When we start looking in countries where multidrug resistance is a serious problem, I think we'll find XDR.” Chris Dye, WHO's Stop TB program

XDR strains of TB have appeared in every part of the world, although they aren't all as virulent. Between 2000 and 2004, 20% of TB strains worldwide were found to be resistant to first-line drugs, and a tenth of those were XDR (MMWR 24, 301–305; 2006).

“When we start looking in countries where multidrug resistance (MDR) is a serious problem, where second-line drugs have been used, I think we'll find XDR,” says Chris Dye, coordinator for TB monitoring and evaluation for the World Health Organization's Stop TB program.

The former Soviet Union, China and India are all prime candidates, Dye says. “It remains to be seen how big the XDR problem is in these countries.”

The answers won't be easy to come by. Most countries don't have the resources and labs to screen people for drug resistance. Even when people are diagnosed by culturing the bacteria, infected individuals can spread the disease during the ten days it takes to get the results.

The South African strain has already been found in other provinces and is very likely to have spread beyond to the neighboring countries of Lesotho, Swaziland and Mozambique.

South Africa has an unhappy mix of conditions that foster TB: the disease thrives in poor, overcrowded townships or mining communities and among those infected with HIV. At 5.3 million, South Africa has an HIV burden second only to India's.

Although South Africa is in many ways better equipped than its neighbors to handle the crises, the government is notoriously negligent toward these concerns and, according to experts on the ground, has done little to protect its citizens from TB or to take full stock of the problem. For example, government clinics don't provide preventive drugs for TB to those on antiretroviral therapy, even though individuals with AIDS are at particular risk of infection.

South Africa's Medical Research Council has been evaluating the country's program for dealing with MDR-TB. “For the large part, the MDR program is unsupervised,” says Richard Chaisson, director of the Johns Hopkins Center for TB Research in Baltimore. “It's an invitation to create XDR-TB, no surprise.”