Overview of TB
According to the World Health Organization (WHO), tuberculosis (TB) is the second most common cause of death from a single infectious agent worldwide. (HIV/AIDS is the number one cause of infectious agent deaths.) Once called consumption, TB is a highly contagious, persistent disease characterized by the formation of hard grayish nodules, or tubercles. The disease is most often caused by the bacterium Mycobacterium tuberculosis and usually occurs in the lungs (the initial site of infection), but it also can occur in other organs. Worldwide incidence of tuberculosis (TB) may have peaked in 2005.
Because its signs and symptoms are easily confused with those of many other (usually respiratory) diseases, tuberculosis can be difficult to diagnose. Common symptoms are cough that is worse in the morning and may include hemoptysis (i.e., blood in the sputum), chest pain, night sweats, and breathlessness (dyspnea). Ninety percent of those infected with M. tuberculosis mount an effective immune response and never develop the disease.
Mycobacterial disease is one of the world's most difficult health problems. According to the WHO, 8.7 million people fell ill with TB in 2011 and 1.4 million people died from the infection. Worldwide, the TB death rate dropped 41 percent from 1990 to 2011 and the estimated number of people falling ill with tuberculosis each year is declininghowever, very slowly. The world is on track to reverse the spread of TB by 2015.
The WHO also reports that more than 95 percent of TB deaths occur in low- and middle-income countries, and it is among the top three causes of death for women aged 15 to 44. In 2010, about 10 million children worldwide were orphaned as a result of TB deaths among parents. Tuberculosis is a leading cause of death in people living with HIV, causing about 25 percent of all deaths in this population. AIDS (autoimmune deficiency syndrome) with coexistent mycobacterial infection is bringing TB back into Western cities and seriously threatens health services in the developing world.
Factors that affect tuberculosis rates in the United States and Europe include the following:
- Emergence of multidrug-resistant strains of M. tuberculosis (called MDR-TB and present in virtually all countries surveyed by the WHO)
- Erosion of systems for diagnosis and treatment of the disease
- Immigration of infected persons from countries where TB is prevalent
- Prevalence of HIV (human immunodeficiency virus) infection and AIDS
- Reactivation of disease in the elderly
- Socioeconomic decline in urban areas
The rapid response of state and federal agencies in the United States has averted a potentially drastic rise in TB incidence.