Tuberculosis (TB) is a common and often deadly infectious disease caused by various strains of mycobacteria in humans. The slow-growing bacteria that cause TB grow best in areas of the body that have lots of blood and oxygen, which is why it is most often found in the lungs (called pulmonary TB). But TB can also spread to other parts of the body, which is called extrapulmonary TB.

Tuberculosis is either latent or active.

• Latent TB means that you have the TB bacteria in your body, but your body’s immune system are keeping it from turning into active TB. This means that you don’t have any symptoms of TB right now and can’t spread the disease to others. If you have latent TB, it can become active TB.
• Active TB means that the TB bacteria are growing and causing symptoms. If your lungs are infected with active TB, it is easy to spread the disease to others.

Pulmonary TB is contagious. It spreads when a person who has active TB breathes out air that has the TB bacteria in it and then another person breathes in the bacteria from the air. An infected person releases even more bacteria when he or she does things like cough or laugh.

If TB is only in other parts of the body (extrapulmonary TB), it does not spread easily to others.

Some people are more likely than others to get TB. This includes people who:

• Have HIV or another illness that weakens their immune system.
• Have close contact with someone who has active TB, such as living in the same house as someone who is infected with TB.
• Care for a patient who has active TB, such as doctors or nurses.
• Live or work in crowded places such as prisons, nursing homes, or homeless shelters, where other people may have active TB.
• Have poor access to health care, such as homeless people and migrant farm workers.
• Abuse drugs or alcohol.
• Travel to or were born in places where untreated TB is common, such as Latin America, Africa, Asia, Eastern Europe, and Russia.

It is important for people who are at a high risk for getting TB to get tested once or twice every year.

Most of the time when people are first infected with TB, the disease is so mild that they don’t even know they have it. People with latent TB don’t have symptoms unless the disease becomes active.

Symptoms of active TB may include:

• A cough that brings up thick, cloudy, and sometimes bloody mucus from the lungs (called sputum) for more than 2 weeks.
• Tiredness and weight loss.
• Night sweats and a fever.
• A rapid heartbeat.
• Swelling in the neck (when lymph nodes in the neck are infected).
• Shortness of breath and chest pain (in rare cases).

Doctors usually find latent TB by doing a tuberculin skin test. During the skin test, a doctor or nurse will inject TB antigens under your skin. If you have TB bacteria in your body, within 2 days you will get a red bump where the needle went into your skin. The test can’t tell when you became infected with TB or if it can be spread to others.

To find pulmonary TB, doctors test a sample of mucus from the lungs (sputum) to see if there are TB bacteria in it. Doctors sometimes take a chest X-ray to help find pulmonary TB.

To find extrapulmonary TB, doctors can take a sample of tissue (biopsy) to test, do a CT scan, or an MRI.

Treatment is often a success, but it is a long process. It takes about 6 to 9 months to treat TB. Most of the time, doctors combine four antibiotics to treat active TB. It’s important to take the medicine for active TB for at least 6 months. Almost all people are cured following this treatment. If tests still show an active TB infection after 6 months, then treatment continues for another 2 or 3 months.

Most people with latent TB are treated with only one antibiotic that they take for 9 months. This reduces their risk for getting active TB.

TB can only be cured if you take all the doses of your medicine. A doctor or nurse may have to watch you take it to make sure that you never miss a dose and that you take it the proper way. You may have to go to the doctor’s office every day, or a nurse may come to your home or work. This is called direct observational treatment. It helps people follow all of the instructions and keep up with their treatment, which can be complex and take a long time. Cure rates for TB have greatly improved because of this type of treatment.

If active TB is not treated, it can damage your lungs or other organs and can be fatal.