Tuberculosis (TB) is an infectious disease of the lungs caused by the bacterium Mycobacterium tuberculosis. In the mid-nineteenth century, about one-fourth of the mortality rate was attributable to tuberculosis. It was particularly rampant in early childhood and young adulthood. Its presence was felt throughout the world, but by the 1940s, with the introduction of antibiotics, there was a sharp decline of cases in developed countries. For less-developed countries with poor public health structures, tuberculosis is still a major problem. Since 1989, however, there has been an increase in reported cases in economically advanced countries due mainly to immunosuppression associated with AIDS, and the emergence of antibiotic-resistant strains of TB.

The bacillus infects the lungs of those who inhale the infected droplets formed during coughing by an individual who has an active case of the disease. It can also be transmitted by unpasteurized milk, as animals can be infected with...