MOSCOW -- A virulent strain of tuberculosis resistant to most available drugs is surfacing around the globe, raising fears of a pandemic that could devastate efforts to contain TB and prove deadly to people with immune-deficiency diseases such as HIV-AIDS.\n\nKnown formally as extensively drug-resistant TB, or XDR-TB, the strain has been detected in 37 countries. It arises when the bacterium that causes TB mutates because antibiotics used to combat it are carelessly administered by poorly trained doctors or patients don't take their full course of medication. Rather than being killed by the drugs, the microbe builds up resistance to them.\n\nAt least 50 percent of those who contract this strain of TB will die of it, according to medical experts. In trying to stop the spread of the disease, which can be transmitted through coughing, spitting or even speaking, health officials have imposed sometimes extreme controls on infected people.