 On a global scale, tuberculosis TB is the single most important infectious cause of morbidity and mortality. The World Health Organization has estimated that one-third of the entire worlds population carries latent TB infection. Of these 8 million develop active disease, and 2 million die from TB each year. In Canada, and most other industrialized countries, the incidence of TB fell dramatically from 1900 until the late 1970s, but since then decline has slowed, and TB continues to cause significant morbidity, and mortality in disadvantaged populations. 