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Tuberculosis

What is it?

Tuberculosis, also known as TB, is a chronic infection with a specific type of bacterium (Mycobacterium tuberculosis) that usually affects the lungs. Although contagious, TB is not as easy to catch as other respiratory infections, since repeated and prolonged exposure to airborne particles from coughing or sneezing is usually necessary to permit sufficient numbers of the bacteria into the lungs.Overcrowded, impoverished living conditions and frequent contact with others who are sick with TB are significant risk factors. In the United States a large proportion of people with TB were born in countries with high rates of the disease. The infection has two distinct stages. First, bacteria are inhaled into the lungs, where most are destroyed by the immune system. Bacteria that are not destroyed are trapped by the immune system inside hard, walled capsules, known as tubercles, which are composed of a number of different types of cells. TB bacteria cannot cause damage or symptoms while encased in the tubercles, and in many people the disease never progresses beyond this point.Only a small fraction (approximately 10 percent) of those infected will develop active disease, the second stage of TB. Active disease appears if the bacteria escape control of the tubercles and infect other sites in the lungs. Bacteria may also invade the bloodstream and the lymphatic system and spread throughout the body. A few people develop active disease within weeks of the initial infection, but in most cases the second stage does not appear until years or decades later. Factors such as aging, a weakened immune system, and poor nutrition increase the risk that the bacteria will break through the tubercle walls. Most commonly, active TB destroys lung tissue and severely impairs breathing, but it may also affect other parts of the body, including the brain, lymph nodes, kidneys, and gastrointestinal tract. Untreated TB may be fatal. Sometimes known as the white plague for the ashen complexion of its victims, TB is a leading killer worldwide despite the development of effective drug treatment. In addition, the disease experienced a resurgence in the United States between 1985 and 1992.With strengthened public health measures, however, the rate of TB has fallen substantially in recent years. A significant factor that contributed to the resurgence of TB, including drug-resistant TB, was nonadherence to treatment by people with the disease. A combination of drugs must be taken for six to nine months to cure the illness. These drugs kill the weakest bacteria first; stronger, more resistant bacteria survive the initial assault and must be attacked steadily over time. However, because symptoms fade after a few weeks, many people do not complete the entire course of treatment. This practice may lead to a relapse with an even more deadly form of the disease. Taking the medication for only a few weeks or months favors survival and growth of the strongest bacteria, creating an infection resistant to some or all drug therapy. To fight TB effectively, and to prevent the growth of drug-resistant strains of the bacteria, it is important that proper courses of treatment are strictly followed. In the United States it is generally recommended that all treatment for TB be directly supervised by a nurse or other health worker to assure compliance. Directly observed therapy (DOT) has been shown to result in high cure rates and low levels of drug resistance. Another major contributor to the resurgence of TB was the AIDS epidemic. The weakened immune defenses of AIDS patients result in the rapid spread of bacteria after an infection.

What Causes It?

  • Bacterial infection causes tuberculosis.
  • TB is spread through the air by the sneeze or cough of a person infected with the bacterium.
  • Those who live in crowded or unsanitary areas, including the poor, migrant farm workers, and the homeless, are at higher risk for TB.
  • People from nations with high rates of TB, such as countries in Latin America, Asia, or Africa, may harbor the TB bacteria and be at risk for becoming sick.
  • People with weakened immune systems, such as those infected with the human immunodeficiency virus (HIV) or undergoing treatment for cancer, are at greater risk for TB.
  • Others at high risk for TB include infants, the elderly, people with diabetes, intravenous drug users, the malnourished, health-care workers, prison guards, and family members of those with TB.
  • TB spreads more easily in confined, poorly ventilated spaces, including jails, nursing homes, tenements, homeless shelters, and even hospitals.

Prevention

  • A vaccine against TB, called BCG, is widely used around the world—but its use is discouraged in the United States. BCG helps reduce the risk of serious TB in children. However, it may provide adults with little or no protection against the disease.
  • Antibiotics may be administered to people who have a positive TB skin test but have no evidence of active disease. These drugs prevent development of second-stage TB by destroying the bacteria trapped within the tubercles. The most commonly used medicine is isoniazid, which should be taken for nine months.

Diagnosis

  • Patient history and physical examination.
  • Chest x-rays.
  • Tuberculin skin test. A small amount of protein derived from mycobacteria is injected into the skin on the arm, and the area is examined after 48 to 72 hours. A slightly raised, hard, red patch of skin at the site indicates the presence of TB (although not necessarily active disease).However, a positive TB skin test may also result from prior immunization with BCG.
  • Sputum smears and culture. Examining sputum for TB bacteria is essential. The smear shows if TB-like organisms are present; smears are negative, however, in many patients who have TB, and some positive smears may be caused by organisms other than TB. The results of the culture may take three to six weeks to develop. A positive culture confirms diagnosis.
  • Bone marrow biopsy. A sample of bone marrow is usually taken from the hip bone.
  • Bronchoscopy (the use of a thin, hollow, flexible tube passed through the mouth into the windpipe to view the main bronchial passages).

How to Treat It

  • A combination of four antibiotics—isoniazid, rifampin, pyrazinamide, and ethambutol, the most effective drugs against TB—is prescribed for six to nine months. After two months the treatment is usually reduced to only isoniazid and rifampin if culture reports indicate that TB will respond to these drugs. The antibiotics must be taken for the full term prescribed, both to cure the infection and to prevent the development of drug-resistant TB strains. Supervised treatment is recommended.
  • Resistant strains of bacteria may require treatment with a combination of additional drugs.
  • Patients should get plenty of rest until symptoms subside.
  • TB sufferers should sneeze or cough into disposable tissues to prevent the spread of infection.
  • Hospitalization in an isolation room with adequate ventilation may be necessary to prevent the spread of TB until the infection has been brought under control.
  • Surgery to remove damaged lung tissue may be performed in advanced cases of drug-resistant TB.

When to Call a Doctor

  • Call a doctor if you develop a persistent cough, chest pain, night sweats, and shortness of breath.
  • If you have been exposed to someone sick with TB, your doctor or local health department can perform a TB skin test.