24 Now more than 125 years since identification of the tubercle bacillus by Robert Koch in 1882, we still cannot become complacent about the disease. It has been estimated that approximately one third of the world’s current population, or over 2 billion people, have been infected (i.e., have either latent or active infection) with the tubercle bacillus, with 8 to 10 million new cases of active tuberculosis and approximately 2 to 3 million deaths occurring worldwide each year. The overwhelming majority of cases of active tuberculosis occur in developing countries. Some 70 million of the 88 million cases of tuberculosis during the 1990s were from Asia and sub-Saharan Africa, where coinfection with the human immunodeficiency virus (HIV) is a major contributor to the increase in infections. Tuberculosis remains an important public health problem in the United States, particularly in indigent and immigrant populations and patients with AIDS (see Chapter 26). Reported cases of tuberculosis in the United States were decreasing until the mid-1980s, at which time the AIDS epidemic and immigration from countries with a high prevalence of tuberculosis combined to result in an increasing frequency of cases. Fortunately, since 1991 the number of cases reported annually in the United States has again been decreasing. Perhaps most alarming, both in the United States and throughout the world, is the relatively recent emergence of drug-resistant strains of the organism, some of which are resistant to multiple antituberculous drugs.
Tuberculosis and Nontuberculous Mycobacteria