Encyclopedia / T / Tuberculosis



Tuberculosis is a chronic infection caused by the bacteria Mycobacterium tuberculosis (and occasionally other variants of Mycobacterium). It usually involves the lungs, but other organs of the body can also be involved.


Today, tuberculosis (TB) tends to be concentrated among inner city dwellers, ethnic minorities and recent immigrants from areas of the world where the disease is still common. Alcoholics, who are often malnourished, are at high risk of developing the disease, as are people infected with HIV. It can occur anywhere, and no one is exempt from the threat of infection.

TB is caused by a germ that is transmitted from person to person by airborne droplets. Usually this infection is passed on as a result of very close contact, so family members of an infected person are endangered if the person continues to live in the same household and has not undergone proper treatment. (The family should take the precaution of seeing a doctor and getting a skin test.)

If an individual with active TB coughs or sneezes without covering the mouth and nose, droplets containing the tuberculosis germs are sprayed into the air and may be inhaled by anyone near the person. A tissue should always be used to cover the nose and mouth when coughing, sneezing or spitting, and hands should be washed promptly.

The vast majority of people who have TB germs in their bodies do not have an active case of the disease. Even if the disease is active, the disease is quite advanced. TB in children often occurs with childhood diseases. A simple skin test is available to detect individuals who have been or are infected with the TB germ. Those who have been infected will have a reaction where the skin becomes swollen. Once infected, most persons will generally test positive for the rest of their lives.

A positive reaction to the tuberculin test does not mean the person is ill or contagious to others. It means that the germs causing tuberculosis have been or are present in the body, and unless other symptoms are evident, the germs are probably not active. Their doctor may want to treat them to eliminate the germs so that a more serious case of active TB can be prevented.


Only about 10 percent of those infected with TB develop the disease. The first symptoms of an active case of TB may be so commonplace that they are often dismissed as the effects of a cold or flu. The individual may get tired easily, feel slightly feverish or cough frequently. It usually goes away by itself, but about in about half the cases, it will return.

For people who have the disease, TB can cause lung or pleural (the lining of the lung) disease or it may spread through the body via the blood. Often people do not seek the advice of a doctor until they have pronounced symptoms, such as pleurisy (a sharp pain in the chest when breathing deeply or coughing) or the spitting up of blood. Neither of these symptoms is solely of tuberculosis, but they should not be ignored. Other symptoms include fever, loss of appetite, weight loss and night sweats.

About 15 percent of people with the disease develop TB in an organ other than the lung, such as the lymph nodes, GI tract, and bones and joints.


If a person has a significant reaction upon being tuberculin skin-tested for the first time, additional laboratory and x-ray examinations are necessary to determine if the individual has active TB.

Tuberculosis can mimic other diseases, such as pneumonia, lung abscesses, tumors and fungal infections, or occur along with them. For a proper diagnosis, therefore, a doctor will rely on symptoms and other physical signs; a person's history of exposure to TB and x-rays that may show evidence of TB infection (usually in the form of lesions or cavities in the lungs). TB bacilli grown in cultures of sputum or other specimens provide a positive diagnosis.


With treatment, the chances of full recovery is good. Although several treatment protocols for active TB are in wide use by specialists, and protocols sometimes change due to advanced in our understanding of optimal therapy, they generally share three principles:

  1. The regimen must include several drugs to which the organisms are susceptible.
  2. The patient must take the medication on a regular basis.
  3. Therapy must continue for a sufficient time.

Also, treatment recommendations are subject to change depending upon both the characteristics of the particular organism being treated and newer advances in therapeutic agents. Thus, consultation on treatment strategies with local public health and infectious disease experts is always advisable.

Isoniazid (INH) is one of the most common drugs used for TB. Inexpensive, effective and easy to take, it can prevent most cases of TB and, when used in conjunction with other drugs, cure most TB. INH preventive treatment is recommended for individuals who have:

  • close contact with a person with infectious TB
  • positive tuberculin skin test reaction and an abnormal chest x-ray that suggests inactive TB
  • a tuberculin skin test that converted from negative to positive within the past two years
  • a positive skin test reaction and a special medical condition (for example, AIDS or HIV infection or diabetes) or who are on corticosteroid therapy
  • a positive skin test reaction, even with none of the above risk factors (in those under 35)

Isoniazid and rifampin are the keystones of treatment, but because of increasing resistance to them, pyrazinamide and either streptomycin sulfate or ethambutol HCL are added to regimens. If the patient is unable to take pyrazinamide, a nine-month regimen of isoniazid and rifampin is recommended.

Even if susceptibility testing reveals that the patient is infected with an isoniazid-resistant strain, the isoniazid component is continued because some organisms may yet be sensitive. In addition, two drugs to which the organisms are likely to be sensitive also are incorporated into the regimen.

The beginning phase of treatment is crucial for preventing the emergence of drug resistance and ensuring a good outcome. Six months is the minimum acceptable duration of treatment for all adults and children with culture-positive TB.

Drug resistance may be either primary or acquired. Primary resistance occurs in patients who have had no previous antimycobacterial treatment. Acquired resistance occurs in patients who have been treated in the past, and it is usually is a result of non-adherence to the recommended regimen or incorrect prescribing.

It has been estimated that one in seven cases of tuberculosis is resistant to drugs that previously cured the disease. Resistance arises when patients fail to complete their drug therapy, lasting six months or longer. The hardiest TB bacteria are allowed to survive as a result, and as they multiply, they spread their genes to a new generation of bacteria - and to new victims.

The drug-resistant forms of TB that do not respond to the usual drug therapy might be treatable by other, sometimes more toxic drugs. Officials of the Center for Disease Control and Prevention call for aggressive intervention to prevent the further spread of drug-resistant TB, including finding "every TB patient" and ensuring that patients complete their drug therapy. To accomplish this, increasing use of directly observed therapy (DOT) is being used - that is, the actual, documented observation of the patient when he or she takes the medicine. This method has been shown to reduce the likelihood of treatment failures.

Overall, it is critical to consult with a physician about the optimal course of therapy for any given case of tuberculosis. In turn, your physician will likely consult with local public health experts to determine if any local circumstances (such as drug-resistant TB) apply to a particular case.


Should a TB test be done?

What medications will you prescribe?

Is my case of TB contagious?

What precautions can be taken to minimize the exposure to TB?

Are there any lasting effects after treatment?