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Wednesday, April 23, 2014
Tuberculosis is a chronic bacterial infection caused by a germ called Mycobacterium tuberculosis. Tuberculosis is an infectious disease that is spread through the air when a person with the disease coughs or sneezes. A person may become infected with TB when they breathe the air droplets from the person who is sick with the disease. The disease commonly infects the lungs but can infect other parts of the body including the spine, brain or kidney. Below are the characteristics of TB infection and TB disease.
Not everyone who becomes infected with tuberculosis becomes sick with the disease itself. This is because the body's immune system is able to keep the number of TB germs low enough to prevent the active disease from developing. The infection at this point is called latent TB infection.
If the TB germs become too numerous for the immune system to contain the person becomes sick with active TB disease.
People with particular health conditions are more likely to develop active disease once infected (see below). The development of active TB disease from latent infection may take months to years to occur. Both TB infection and disease can be readily diagnosed and treated.
Active tuberculosis infection is generally treated with 4 antibiotics, given for 6-12 months, depending upon the patient's ability to tolerate the medication. These medications are:
Sometimes the tuberculosis infection does not respond to some of the antibiotics listed above. The laboratory can test the tuberculosis bacteria for the effectiveness of the antibiotics that are routinely used. If drug resistant tuberculosis is detected, more potent antibiotics must be used, often for longer periods of time.
Drug resistance develops when a person who is sick with tuberculosis does not take all their medications as instructed. This is why it is extremely important for tuberculosis patients to take all their medications. Most tuberculosis treatment programs provide the tuberculosis medications and watch the patient take all their pills. This is called directly observed therapy. This is the best way to prevent the development of drug resistant tuberculosis.
The interferon gamma release assay (IGRA) tests are blood tests that detect the ability of the immune system to recognize the tuberculousis infection. The advantage to these blood tests is that they do not require a follow up visit (like the visit needed to read the TB skin test). In addition the IGRA tests are useful in patients who have recieved the BCG vaccine because the IGRA tests do not cress react with the vaccine which can be a problem with the PPD. The IGRA test is done instead of a PPD. A positive IGRA test typically indicates latent TB infection.
Many research studies are underway to help us learn about tuberculosis. Would you like to find out more about being part of this exciting research? Please visit the following links:
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Last Reviewed: Oct 04, 2011
Catherine A Curley, MD, MS
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University
Allan B Chiunda, MPH
Case Western Reserve University