Approximately 20 million people worldwide have tuberculosis (TB), and it is responsible for 3 million deaths worldwide annually. In the United States, approximately 15 million people are infected with M. tuberculosis, with more men infected than women. The incidence is highest among Asians and Pacific Islanders, followed by African Americans, Hispanics, Native Americans, and whites. The incidence of TB is rising in the United States because of the emergence of drug-resistant strains. Fifteen percent of people infected with TB in the United States have a drug-resistant strain. Hospitals and correctional facilities in Florida and New York have reported outbreaks of drug-resistant strains of TB with a mortality rate of 70-90% and a mean survival time of 4-16 weeks.

TB is often classified as an opportunistic infection because it is likely to develop in someone with a weakened immune system. People at high risk for contracting TB are those with acquired immunodeficiency syndrome, malnutrition, diabetes, and/or alcoholism. Poverty, overcrowding, homelessness, and drug abuse also place people at risk for the disease.

TB may be classified as primary (i.e., disease occurs 2 years after infection), reactivation (i.e., disease occurs later than 2 years after infection), pulmonary (i.e., disease occurs in the lungs), or extrapulmonary/miliary (i.e., disease occurs in other tissues). Transmission of TB occurs via airborne droplets when a person with active disease, approximately 5% to 15% of those infected, talks, sings, coughs, or sneezes. High concentrations of the bacilli in the air, such as in small, closed, nonventilated areas, and numerous exposures to the bacilli increase the risk for transmission of the infection.