Tuberculosis (TB) is an infectious disease caused by a germ (bacterium) called Mycobacterium tuberculosis. This germ primarily affects the lungs and may infect anyone at any age.
In the United States, the number of TB cases steadily decreased until 1986 when an increase was noted; TB has continued to rise since. Today, ten million individuals are infected in the U.S., as evidenced by positive skin tests, with approximately 26,000 new cases of active disease each year. The increase in TB cases is related to HIV/AIDS, homelessness, drug abuse and immigration of persons with active infections.
How is TB Contracted?
TB is a contagious or infectious disease that is spread from person-to- person. A person is usually infected by inhaling the germs which have been sprayed into the air by someone with the active disease who coughs.
However, inhaling the germ does not usually mean you will develop active disease. A person's natural body defenses are usually able to control the infection so that it does not cause disease. In this case, the person would be infected, but not have active disease. Only about 10% of those infected will actually develop TB in their lifetimes.
Active disease can occur in an infected person when the body's resistance is low or if there is a large or prolonged exposure to the germs that overcome the body's natural defenses. The body's response to active TB infection produces inflammation which can eventually damage the lungs. The amount of damage may be quite extensive, yet the symptoms may be minimal. The usual symptoms of disease due to TB are:
-Fever -Night sweats -Cough -Loss of appetite -Weight Loss -Blood in the sputum (phlegm) -Loss of energy
To diagnose TB, your clinician will gather five important pieces of information:
-Symptoms -History of possible exposure and onset of symptoms -Tuberculin skin test or PPD -Chest X-ray Sputum test
Tuberculin Skin Test
The tuberculin skin test (or PPD) is performed with an extract of killed tuberculosis germs that is injected into the skin. If a person has been infected with tuberculosis, a lump will form at the site of the injection--this is a positive test. This generally means that TB germs have infected the body. It does not usually mean the person has active disease. People with positive skin tests but without active disease cannot transmit the infection to others.
If a person has been infected with TB, but active disease has not developed, the chest X-ray usually will be normal. Most people with a positive PPD have normal chest X-rays and continue to be healthy. For such persons, preventive drug therapy may be recommended.
However, if the germ has attacked and caused inflammation in the lungs, an abnormal shadow is usually visible on the chest X-rays. For these persons, aggressive diagnostic studies (sputum tests) and treatment usually are appropriate.
Samples of sputum coughed up from the lungs can be tested to see if TB germs are present. The sputum is examined under a microscope (a "sputum smear") to look for evidence of the presence of TB organisms. The organisms are then grown in the laboratory to identify them as TB germs and to determine what medications are effective in treating them. These studies are referred to as culture and susceptibility testing. State health department laboratories and reference laboratories can perform such testing.
Treatment of TB
Individuals with a positive tuberculin skin test may or may not receive preventive drug therapy depending on the exposure history, the timing of the skin test conversion (when the test changes from negative to positive) and other factors in the individual's medical history. When it is known that a person has recently been in close contact with an individual with active tuberculosis and has developed a positive tuberculin skin test, preventive treatment is advisable due to a relatively high...
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