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Most people are familiar with tuberculosis, which is a disease caused by the bacterium, Mycobacterium tuberculosis. The germ is spread by air borne transmission, when an infected person coughs or sneezes. This same bacterium causes latent tuberculosis (TB) infection. Individuals with latent TB do not have any symptoms and do not have TB disease.
What is Latent Tuberculosis (TB) Infection?
Latent TB infection is an infectious disease infection that has been contained by the host’s immune system. The bacteria are inactive. Individuals with latent TB infection are not contagious and cannot spread the infection to others.
Tuberculosis usually affects the lungs, but it can affect other parts of the body, such as the brain, the kidneys or the spine. As long as the immune system functions normally, an infected person will not have symptoms. However, if the immune system fails in fighting off the tuberculosis germs, the infection becomes active tuberculosis disease. This can happen at any time.
The CDC estimated 5 to 10 percent of untreated cases of latent TB infection will develop TB disease at some time in life. About half of these individuals will convert to active TB within the first two years of infection. The risk is considerably higher for people with weak immune systems.
If Latent TB infection Does Not Cause Symptoms, How is it Diagnosed?
A person with latent TB infection usually has a skin test or blood test result indicating the infection. She has a normal chest x-ray and a negative sputum test. She will not feel sick.
Targeted tuberculosis testing for latent TB infection identifies persons at high risk for developing tuberculosis. The high risk group includes people who have had a recent infection with Mycobacterium tuberculosis or who have clinical conditions that increase the risk for infection, patients with organ transplants and immunosuppressed patients.
Two tests are used to detect the infection. The skin test is used most often. A small needle is inserted under the skin. The special needle contains tuberculin, which is a special testing material. In two to three days, the site is examined by your health care provider.