Despite improvements in the prognosis of TB in affluent nations, the disease continues to be the leading cause of death among bacterial infections worldwide. Further-more, about 2 billion people harbor latent M. tuberculosis, constituting a reservoir that has been estimated will result in about 100 million cases of reactivation TB. The World Health Organization (WHO) esti-mates that of about 50 million deaths occur-ring each year, about 2 million are from TB and over 95 percent of those deaths occur in the developing world. TB epidemics are extremely slow, typically expanding over centuries. Although the incidence of TB worldwide was in a downtrend since the 1950s, this has changed considerably in recent times: from 1985 to 1992 the inci-dence of TB rose by 20 percent in the United States, and a considerable percentage of the cases were drug-resistant. Among the most important reasons for such reversal were the AIDS pandemic, reduction in public health resources in inner cities, and continued immigration from areas of high TB prevalence.