Sanjay Basu and the research team at the Yale School of Medicine in New Haven, Conn., developed a computer model using data from South Africa where XDR TB is prevalent to determine the extent of the spread of the highly contagious disease in that country.

Cases of XDR TB have been diagnosed in every province of South Africa and are particularly concentrated in the area surrounding Tugela Ferry.

The Yale School of Medicine researchers said that the use of masks alone would prevent fewer than 10 percent of cases in the general epidemic but would help many healthcare workers. Reducing time spent in the hospital and shifting to outpatient therapy could prevent nearly one-third of cases. In addition, one-half of XDR TB cases could be prevented by addressing hospital overcrowding, improving ventilation, enhancing access to HIV treatment, and providing faster diagnostic tests, the study said.

The findings are published in The Lancet.