Tuberculosis (TB)
What Happens
Tuberculosis (TB) develops when Mycobacterium tuberculosis bacteria are inhaled into the lungs. The infection usually stays in the lungs. But the bacteria can travel through the bloodstream to other parts of the body (extrapulmonary TB).
An initial (primary) infection can be so mild that you don't even know you have an infection. In a person who has a healthy immune system, the body usually fights the infection by walling off (encapsulating) the bacteria into tiny capsules called tubercles. The bacteria remain alive but cannot spread to surrounding tissues or other people. This stage is called latent TB, and most people never go beyond it.
A reaction to a tuberculin skin test is how most people find out they have latent TB. It takes about 48 hours after the test for a reaction to develop, which is usually a red bump where the needle went into the skin. Or you could have a rapid blood test that provides results in about 24 hours.
If a person's immune system becomes unable to prevent the bacteria from growing, the TB becomes active. Of people who have latent TB, 5% (1 person out of 20) will develop active TB within 2 years after the initial infection. Another 5% of people who have latent TB will develop active TB at some point in their lives.1
People who have latent TB may be at risk for the active disease if they:
- Have an impaired immune system. The immune system may be weakened in older adults, newborns, women who have recently given birth, and people who have HIV infection, some cancers, or poorly controlled diabetes.
- Have poor access to health care, such as homeless people, migrant farm workers, or people who abuse alcohol or drugs.
- Take some types of medicines, such as long-term corticosteroids, tumor necrosis factor-alpha antagonists (used to treat rheumatoid arthritis or Crohn's disease), or medicines to prevent rejection of a transplanted organ.
- Have a chronic lung disease caused by breathing in tiny sand or silica particles (silicosis) or celiac disease.2
- Have had gastric bypass surgery or a gastrectomy.
- Are 10% or more under their healthy body weight.
Active TB in the lungs
Active TB in the lungs (pulmonary TB) is contagious. TB spreads when a person who has active disease exhales air that contains TB-causing bacteria and another person inhales the bacteria from the air. These bacteria can remain floating in the air for several hours. Coughing, sneezing, laughing, or singing releases more bacteria than breathing. TB is more likely to spread when:
- People are living together in crowded conditions. TB can spread rapidly in nursing homes, hospitals, homeless shelters, schools, military barracks, and prisons.
- People live in the same house with a person who has active TB. This increases the chance of inhaling TB-causing bacteria and developing an infection. TB is not spread by handling objects that have been touched by a person who has TB.
In general, after 2 weeks of treatment with antibiotics, you cannot spread an active pulmonary TB infection to other people.
Skipping doses of medicine can delay a cure and cause a relapse. In these cases, you may need to start treatment over. Relapses usually occur within 6 to 12 months after treatment. Not taking the full course of treatment also allows antibiotic-resistant strains of the bacteria to develop, making treatment more difficult.
Without treatment, active TB can cause serious complications, such as:
- Pockets or cavities that form in the lungs. These damaged areas may cause bleeding in the lungs or may become infected with other bacteria and form pockets of pus (abscesses).
- A hole that forms between nearby airways in the lungs.
- Difficulty breathing because of blocked airways.
TB can be fatal if it is not treated.
Active TB outside the lungs
Active TB in parts of the body other than the lungs (extrapulmonary TB) is not spread easily to other people. You take the same medicines that are used to treat pulmonary TB. You may need other treatments depending on where in your body the infection is growing and how severe it is.
TB in certain groups of people
Infants and children and people with HIV or AIDS who have active TB need special care.
 Go to previous section |  Go to top of page |  Go to next section |
| Author: | Maria G. Essig, MS, ELS | Last Updated: April 23, 2009 |
| Medical Review: | Caroline S. Rhoads, MD - Internal Medicine R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care, Medical Toxicology | |
 | ||
