Tuberculosis (TB) is a chronic bacterial infection that usually infects the lungs, although other organs such as the kidneys, spine or brain sometimes are involved. Considered one of the world's deadliest infectious diseases, TB and complications from the disease kill about 1.5 million people globally each year. Additionally, drug-resistant tuberculosis is a growing problem. The World Health Organization (WHO) estimates that nearly 5 percent of all TB cases worldwide are multidrug-resistant, with 440,000 cases occurring annually.
The predominant TB bacterium is Mycobacterium tuberculosis (M. tuberculosis). It is spread through the air when an infected person coughs, sneezes, speaks, sings or laughs; however, repeated exposure to the germ usually is necessary before you will become infected.
You are not likely to become infected through clothing, bedding, a drinking glass, eating utensils, a handshake, a toilet or other items that a person with TB has touched.
Adequate ventilation is the most important measure to prevent the transmission of TB.
Three stages of tuberculosis
There is a difference between being infected with the TB bacterium and having active tuberculosis disease. The three stages of TB include:
- Exposure – This occurs when you have been in contact with or have been exposed to someone who has TB. You will have a negative skin test, a normal chest X-ray and no signs or symptoms of the disease.
- Latent TB infection – This occurs when you have TB bacteria in your body but have no symptoms of the disease. The immune system walls off the TB organisms, which remain dormant for life in 90 percent of people who are infected. If you have latent TB infection, you will have a positive skin test but a normal chest X-ray.
- TB disease – If you have TB disease, you have signs and symptoms of an active TB infection. You will have a positive skin test and a positive chest X-ray.
Many people infected with M. tuberculosis never develop active TB and remain in the latent TB infection stage. However, in people with weakened immune systems, especially those with human immunodeficiency virus (HIV), TB organisms can overcome the body’s defenses, multiply and cause an active disease.
Tuberculosis affects all ages, races, income levels and both genders. Although TB rates fell to an all-time low in the United States in 2011, the disease continues to disproportionately infect racial and ethnic minorities, those who are foreign-born and people infected with HIV.
Those at higher risk for tuberculosis include:
- People who live or work with others who have TB
- Medically underserved populations
- Homeless people
- People from other countries where TB is prevalent
- People in group settings, such as nursing homes
- People who abuse alcohol
- People who use intravenous drugs
- People with impaired immune systems
- Senior citizens
- Health care workers who come in contact with high-risk populations