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How is TB Spread? | Print |

If a person is diagnosed with latent TB infection it means that the person has inhaled TB bacteria and become infected with TB, but only has dormant (sleeping) TB bacteria in their body. However, not everyone who is exposed to the bacteria develops latent TB infection. In general, close contacts or persons with prolonged, frequent, or intense contact are at highest risk of becoming infected.

The dormant TB bacteria in the body are kept under control by the body’s immune system. The immune system does this by producing special immune cells that surround the TB bacteria. The cells form a hard shell that keeps the bacteria contained and under control. These dormant bacteria are not making them sick, and they cannot pass these bacteria to anyone else. A person with LTBI only, is not regarded as a case of TB. Many who have LTBI only--- never develop tuberculosis disease. In these people, the TB bacteria can remain inactive for a lifetime without causing disease.

People with Latent TB Infection (LTBI)

  • Have no symptoms
  • Don't feel sick
  • Can't spread TB to others
  • Usually have a positive skin test reaction or QuantiFERON-TB Gold test (QFT-G)
  • May develop active TB disease if they do not receive treatment for latent TB infection

What is TB Disease?

Some people diagnosed with latent TB infection will develop TB disease. TB disease develops when the immune system cannot keep the dormant bacteria under control and the bacteria begin to rapidly multiply and destroy tissue in their body; the bacteria can actually create a hole in the lung. People with TB disease are sick and usually have symptoms of TB disease.

TB disease can develop very soon after infection or many years after infection. In the United States, older people, persons with issues of substance abuse, HIV infection, or cancer are more likely to progress from latent TB infection to active TB disease. People with a history of TB exposure have about a 10% risk, over their lifetime, of developing active TB disease. People with HIV and a history of TB exposure have about a 10% risk each year of life of developing active TB disease.

People with TB Disease

  • Usually have signs and symptoms
  • Usually feel sick
  • May spread TB bacteria to others
  • Usually have a positive skin test reaction or QuantiFERON-TB Gold test (QFT-G)
  • May have an abnormal chest x-ray, or positive sputum smear or culture
  • Need treatment to treat active TB disease¬†

TB disease normally affects the lung and is called pulmonary TB. When TB occurs outside the lung it is referred to as extra pulmonary TB. TB in the lungs or throat can be infectious; meaning that the bacteria can be spread to other people. People with TB disease are most likely to spread it to people they spend time with every day, including family members, friends, and coworkers. TB disease in other parts of the body, such as the kidney or spine, is usually not infectious. TB is a serious illness; it is important to identify people who have active TB disease so they can be treated, preventing further spread of the bacteria and future cases of TB.

TB is contagious, but not as contagious as other diseases such as the flu or chickenpox. To get infected, a person usually has to spend many hours over an extended period of time with the person who has infectious TB disease. You must inhale the infectious droplet to become infected. People who live in overcrowded housing with poor air circulation may be more at risk of getting TB infection. The probability that TB will be transmitted heavily depends on these other factors:

  • Infectiousness of the person with TB disease
  • Environment in which exposure occurred
  • Duration of exposure
  • Virulence of the organism




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