Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis organisms. Because the body's defense system has difficulty fighting this particular type of bacterium, the body attempts to wall off invading organisms within small nodules, called granulomas or tubercles, which contain both the infecting bacteria and the tissue produced by the body in reaction to them.

Of all people who are infected by the tuberculosis bacteria, 80 percent will never experience the symptoms of the disease. Usually, the body is able to surround the offending bacteria with granulomas; the tuberculosis bacteria then lie dormant in the body, and active disease does not develop. However, because the body cannot actually kill the tuberculosis bacteria, the infection can become active at a later time, often when some other disease has caused a weakening of the body's defenses.

Of the 20 percent of infected people in whom an active case of tuberculosis does develop, only half will become sick within three months of contracting the infection; the other half will suffer from the disease at some other time in their lives, perhaps years later. Tuberculosis usually affects the lungs, but it can also involve other parts of the body, such as the spine, the kidneys, the digestive tract, and the lining of the heart.

Causes

Tuberculosis is contracted when a person breathes in droplets containing Mycobacterium tuberculosis organisms that have been coughed or sneezed into the air by an infected person. Tuberculosis is contagious, especially for people living in crowded conditions. Also highly susceptible to this disease are those who are undernourished, in poor health, or living in poor urban areas, as well as the very young, the very old, and those in the medical professions.

Anyone who has been in close contact with a tuberculosis patient should be tested for the infection.

Symptoms

Early signs include fever, fatigue, loss of appetite, and weight loss. Later signs include coughing up of blood-tinged sputum, chest pain, and shortness of breath.

Diagnosis

The symptoms of tuberculosis are similar to those of many other diseases, and its characteristic symptoms do not appear until the disease is in its advanced stages. For these reasons, coupled with the fact that the incidence of tuberculosis has been declining in recent years in the United States, this disorder often remains untreated or misdiagnosed for some time.

Patients can be tested for tuberculosis with a tuberculin skin test. If the bacteria are present, whether active or inactive, the patch of skin that has been treated with dead tuberculosis bacteria will swell. Chest X-rays or sputum analysis may also help to identify the site of infection.

Treatment

Tuberculosis is treated with a variety of antibacterial drugs simultaneously. Each type of medication acts individually on a different portion of the tuberculosis bacterium; only in combination do these drugs have the greatest probability of eliminating the infection. The drugs are prescribed for a long period of time, perhaps 6 to 18 months, but usually after two weeks the patient is no longer contagious and can resume normal activities.

With this type of treatment, the disease is rarely fatal. (When an infected individual does not complete drug therapy, however, new, drug-resistant strains of tuberculosis may develop.) Severe side effects, such as liver or hearing damage, can result from certain antituberculosis drugs.

Prevention

An active case of tuberculosis can be prevented in some high-risk people by the administration of certain antituberculosis drugs, but these drugs are likely to have undesirable side effects in many of the people who take them. (High-risk people include those under the age of 35, especially children, who have been exposed to the disease, as well as those with chronic diseases that have weakened their respiratory or immune systems.)

Liver damage that can be caused by these drugs is more likely to occur in those older than the age of 35, so people in this age group need to be monitored closely if they receive these medications.

Regardless of age or physical condition, however, anyone who has been in close contact with a person who has an active case of tuberculosis should be tested for the disease.