(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.
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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
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%
to 10% (1 to 2 people out of 20) will develop active TB at
some point in their lives.1
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
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.
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.