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Tuberculosis (TB)


The Manual's Editorial Staff

Reviewed/Revised Sep 2022
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What is tuberculosis?

Tuberculosis (TB) is a common, serious infection caused by bacteria called Mycobacterium tuberculosis.

What are the stages of TB?

Tuberculosis has 3 stages:

  • Primary infection

  • Latent infection

  • Active disease

In primary infection, the TB bacteria enter your lungs and sometimes spread to other parts of your body. Only a few people with primary infection get sick.

In latent infection, the body's defenses (immune system Overview of the Immune System The immune system is your body's defense system. It helps protect you from illness and infection. The immune system's job is to attack things that don’t belong in your body, including: Germs... read more ) attack the TB bacteria and seal them off inside small clumps of scar tissue. Your body may eventually kill the bacteria, but the bacteria often stay alive and inactive for many years. About 5 to 10% of people with latent infection get active disease.

In active disease, bacteria that were sealed off inside clumps of scar tissue become active and break free. Active disease makes you sick and able to spread the infection to others.

What causes TB?

TB is caused by breathing in the tuberculosis bacteria, Mycobacterium tuberculosis.

The bacteria gets into the air when a person with active disease coughs, sneezes, or even just talks.

Why does TB become active?

Diseases and drugs that weaken your immune system make TB more likely to become active.

The most common risk factor is:

Other risk factors include:

  • Diabetes

  • Severe kidney failure

  • Certain cancers

  • Drugs such as corticosteroids and new inflammation-blocking drugs

Sometimes TB becomes active even if you don't have risk factors.

What are the symptoms of TB?

TB usually doesn't cause symptoms right away. In fact, most people who are infected will never have symptoms.

If you have symptoms, they usually involve your lungs. You may have:

  • Cough, sometimes with yellow or green mucus streaked with blood

  • Fever

  • Night sweats

  • Weight loss

  • Feeling unwell, low-energy, and not hungry

  • Shortness of breath and chest pain

Less often, you'll have symptoms due to the infection involving other organs that are infected with the TB bacteria. For example, kidney infection causes back pain and blood in your urine. Brain infection causes headache, confusion, and drowsiness. Spine infection causes back pain.

How do doctors tell if I have TB?

If you have symptoms that might be TB, doctors look for active disease using:

  • A chest x-ray

  • A sample of your sputum (mucus you cough up) to test for TB bacteria

If the results of these tests aren't clear, doctors may do a TB skin test or a blood test.

The TB skin test is called a PPD (purified protein derivative). A health care worker injects a little bit of protein from TB bacteria just under the skin of your arm. If you've been exposed to TB, in about 2 days you get a hard bump in the area.

What are screening tests for TB?

Screening tests look for disease in people who don't have any symptoms. Because TB often doesn't cause any symptoms, you need regular screening tests if you're at risk for TB.

You might need a screening test if you:

  • Had close contact with someone with active TB

  • Are a health care worker

  • Have HIV infection, diabetes, or other diseases that increase your risk of TB

  • Take certain drugs that weaken your immune system

  • Come from a country where a lot of people have TB

Screening tests include:

  • TB skin test

  • TB blood test

  • Sometimes, a chest x-ray

If your skin or blood test is positive, doctors examine you and do a chest x-ray to see if you have active disease. If you don't have active disease, the positive screening test means you have a latent infection.

How do doctors treat TB?

Active TB

TB is treated with antibiotics. There are many different antibiotic regimens doctors use to treat active TB depending on your disease, test results, and other circumstances. But in general you'll:

  • Be treated at home

  • Take 4 antibiotics for about 2 months

  • Then take at least 2 antibiotics for another 4 to 7 months—it takes a long time to get rid of all the TB bacteria

You may need to be in the hospital if you're very sick, have no place to live, or live someplace where it's hard to limit who you're in contact with. For example, if you live in a nursing home, dormitory, or shelter.

Latent TB

Even though you don't feel sick with latent TB, doctors usually treat you if your screening test recently became positive. You need treatment so the TB doesn't become active. Typically doctors will have you:

  • Take a single antibiotic for 4 or 9 months (depending on which antibiotic they use)

What are resistant bacteria?

Some strains of TB have transformed so they can no longer be killed off by common antibiotics. These strains of drug-resistant TB must be treated for a very long time with 4 or 5 different antibiotics.

How do doctors prevent TB from spreading?

Unless your TB infection is extremely resistant to drugs, you won't spread it to healthy people after you've been taking antibiotics for a week or two. Until then, you need to take some precautions.

If you're treated at home:

  • Don't have visitors

  • Cover your cough (with a tissue or by coughing into your elbow)

If you live with people at high risk, such as young children or people with HIV, you may need to take precautions until tests show the TB is under control.

If you're being treated in the hospital, you may also have to:

  • Be in an isolation room where people coming in have to wear a special respirator mask (not just a regular surgical mask)

Is there a vaccine for TB?

There is a vaccine for TB Vaccination for tuberculosis Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs, but almost any organ can be involved. Tuberculosis... read more Vaccination for tuberculosis . It's called BCG. However, it makes your PPD skin test turn positive. So if you've had the vaccine, doctors can't use the skin test to screen you for TB. Because of this, the vaccine is used mainly for children in countries where TB is common.

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