TB is spread through the air from one person to another. The bacteria are put into the air when a person with active TB disease of the lungs or throat coughs or sneezes. People nearby may breathe in these bacteria and become infected. When a person breathes in TB bacteria, the bacteria can settle in the lungs and begin to grow. From there, they can move through the blood to other parts of the body, such as the kidney, spine, and brain.

TB in the lungs or throat can be infectious. This means that the bacteria can be spread to other people. TB in other parts of the body, such as the kidney or spine, is usually not infectious. People with active TB disease are most likely to spread it to people they spend time with every day. This includes family members, friends, and coworkers.

Symptoms of TB depend on where in the body the TB bacteria are growing. TB bacteria usually grow in the lungs. TB in the lungs may cause:

• a bad cough that lasts longer than 2 weeks
• pain in the chest
• coughing up blood or sputum (phlegm from deep inside the lungs)

Other symptoms of TB disease are:

• weakness or fatigue
• weight loss
• no appetite
• chills
• fever
• sweating at night

In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection

• have no symptoms
• don't feel sick
• can't spread TB to others
• usually have a positive skin test reaction
• can develop active TB disease if they do not receive treatment for latent TB infection

Many people who have latent TB infection never develop active TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weak immune systems, the bacteria become active and cause TB disease.

The best way to remember to take your medicine is to get Directly Observed Therapy (DOT). If you get DOT, you will meet with a health care worker every day or several times a week. You will meet at a place you both agree on. This can be the TB clinic, your home or work, or any other convenient location. You will take your medicine at this place while the health care worker watches.

DOT helps in several ways. The health care worker can help you remember to take your medicine and complete your treatment. This means you will get well as soon as possible. With DOT, you may need to take medicine only 2 or 3 times each week instead of every day.

The health care worker will make sure that the medicine is working as it should. This person will also watch for side effects and answer questions you have about TB.

Even if you are not getting DOT, you must be checked at different times to make sure everything is going well. You should see your doctor or nurse regularly while you are taking your medicine. This will continue until you are cured.

DOTS, is the internationally recommended strategy to control TB. DOTS has five components:

• political commitment to sustained TB control
• access to quality-assured TB sputum microscopy
• standardized short-course drug treatment, including direct observation of therapy
• an uninterrupted supply of quality-assured drugs
• a standardized recording and reporting system, enabling assessment of outcome in all patients.

Bacille Calmette-Guerin vaccine currently is the only vaccine available for TB. Although this vaccine is not widely used in the United States or Northern Europe, WHO recommends that BCG be given to infants and young children in countries where TB is common. The BCG vaccine does not always protect people from TB, and it should not be given during pregnancy or to children with symptomatic HIV infection.

Although BCG appears to reduce the risk of serious childhood forms of TB, BCG does not seem to be highly effective as people move into adulthood. Efforts to develop a more effective TB vaccine are underway, and researchers hope to make such a vaccine available within a decade.

There are two possible ways a person can develop TB disease.  The first applies to a person with latent TB infection -- when a person might have been infected with TB for years but has otherwise been healthy and without symptoms. However, it is possible for latent TB infection to become active at any time, particularly if a person's immune system is weakened. In this way, a person might become sick with TB disease months or even years after they first breathed the TB bacteria.

The other way TB disease develops happens much more quickly. Sometimes when a person first breathes in the TB bacteria the body is unable to protect itself against the disease. The bacteria then develop into active TB disease within weeks.

Active TB disease – an illness in which TB bacteria are multiplying and attacking different parts of the body. The symptoms of active TB disease include weakness, weight loss, fever, no appetite, chills, and sweating at night. Other symptoms of active TB disease depend on where in the body the bacteria are growing. If active TB disease is in the lungs (pulmonary TB), the symptoms may include a bad cough, pain in the chest, and coughing up blood. A person with active TB disease may be infectious and spread TB to others.

BCG – a vaccine for TB named after the French scientists who developed it, Calmette and Guérin. BCG is not widely used in the United States, but it is often given to infants and small children in other countries where TB is common.

Chest x-ray – a picture of the inside of your chest. A chest x-ray is made by exposing a film to x-rays that pass through your chest. A doctor can look at this film to see whether TB bacteria have damaged your lungs.

Contact – a person who has spent time with a person with infectious TB.

Culture – a test to see whether there are TB bacteria in your phlegm or other body fluids. This test can take 2 to 4 weeks in most laboratories.

Directly observed therapy (DOT) – a way of helping patients take their medicine for TB. If you get DOT, you will meet with a health care worker every day or several times a week. You will meet at a place you both agree on. This can be the TB clinic, your home or work, or any other convenient location. You will take your medicine while the health care worker watches.

Extrapulmonary TB – active TB disease in any part of the body other than the lungs (for example, the kidney, spine, brain, or lymph nodes).

HIV infection – infection with the human immunodeficiency virus, the virus that causes AIDS (acquired immunodeficiency syndrome). A person with both latent TB infection and HIV infection is at very high risk for active TB disease.

INH or isoniazid – a medicine used to prevent active TB disease in people who have latent TB infection. INH is also one of the four medicines often used to treat active TB disease.

Latent TB infection – a condition in which TB bacteria are alive but inactive in the body. People with latent TB infection have no symptoms, don't feel sick, can't spread TB to others, and usually have a positive skin test reaction. But they may develop active TB disease if they do not receive treatment for latent TB infection.

Multidrug-resistant TB (MDR TB) –active TB disease caused by bacteria resistant to two or more of the most important medicines: INH and RIF.

Mycobacterium tuberculosis– bacteria that cause latent TB infection and active TB disease.

Negative – usually refers to a test result. If you have a negative TB skin test reaction, you probably do not have TB infection.

Positive – usually refers to a test result. If you have a positive TB skin test reaction, you probably have TB infection.

Pulmonary TB – active TB disease that occurs in the lungs, usually producing a cough that lasts 3 weeks or longer. Most active TB disease is pulmonary.

QuantiFERON-TB ® Gold (QFT) – a blood test used to find out if you are infected with TB bacteria. The QFT measures the response to TB proteins when they are mixed with a small amount of blood.

Resistant bacteria – bacteria that can no longer be killed by a certain medicine.

Smear – a test to see whether there are TB bacteria in your phlegm. To do this test, lab workers smear the phlegm on a glass slide, stain the slide with a special stain, and look for any TB bacteria on the slide. This test usually takes 1 day to get the results.

Sputum – phlegm coughed up from deep inside the lungs. Sputum is examined for TB bacteria using a smear; part of the sputum can also be used to do a culture.

TB skin test – a test that is often used to detect latent TB infection. A liquid called tuberculin is injected under the skin on the lower part of your arm. If you have a positive reaction to this test, you probably have latent TB infection.

Tuberculinor PPD – a liquid that is injected under the skin on the lower part of your arm during a TB skin test. If you have latent TB infection, you will probably have a positive reaction to the tuberculin.