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What is tuberculosis?

Tuberculosis (TB), once called "consumption," is a highly infectious disease that primarily affects the lungs. According to the World Health Organization (WHO), it’s the most deadly infectious disease in the world, killing 1.5 million people in 2014. TB is most common in developing countries, but people in the United States are diagnosed with the condition each year.

Tuberculosis is usually preventable and curable under the right conditions.

What are the symptoms of tuberculosis?

Some people carry the TB bacteria but don’t experience symptoms. This condition is known as latent TB. TB can stay dormant for years before developing into active TB.

Active TB causes many symptoms that are most commonly related to the respiratory system, including coughing up blood or sputum (phlegm). You may experience a cough that lasts for over three weeks and pain when coughing or during normal breathing.

Other symptoms include:

  • unexplained fatigue
  • fever
  • night sweats
  • appetite loss
  • weight loss

While TB usually affects the lungs, it can also affect other organs, such as the kidneys, spine, and brain. Symptoms will vary depending on which organ is infected. For example, tuberculosis of the kidneys can cause you to urinate blood.

Who is at risk for tuberculosis?

According to WHO, more than 95 percent of all diagnosed TB cases occur in developing countries.

People who use tobacco or are long-term drug or alcohol abusers are more likely to get active TB, as are people diagnosed with HIV or AIDS. TB is the leading killer of people who are HIV-positive, killing 1 in 3 people, according to WHO. Other risk factors for getting TB include:

  • diabetes
  • end-stage kidney disease
  • malnourishment
  • certain cancers

Medications that suppress the immune system can also put people at risk for developing active TB, in particular medications that help prevent organ transplant rejection. Other medications that increase your risk of getting TB include those taken to treat:

  • cancer
  • rheumatoid arthritis
  • Crohn’s disease
  • psoriasis

Traveling to regions where TB rates are high also increases your risk of contracting the infection. These regions include:

  • sub-Saharan Africa
  • India
  • Mexico and other Latin American countries
  • China and many other Asian countries
  • parts of the former Soviet Union
  • islands of Southeast Asia
  • Micronesia

According to the Mayo Clinic, some low-income groups in the United States have limited access to resources needed to diagnose and treat TB, placing them at greater risk of TB infection. People who are or have been homeless or in prison are at a higher risk of developing TB.

What causes tuberculosis?

A bacteria called Mycobacterium tuberculosis causes TB. There are a variety of TB strains, and some are resistant to medication.

TB bacteria are transmitted through the air. Once they’re in the air, a nearby person can inhale them. They can be transmitted via:

  • sneezing
  • coughing
  • speaking
  • singing

People with strong immune systems may not experience TB symptoms, even though they carry the bacteria. This is known as latent or inactive TB. According to WHO, about one-third of the world’s population has latent TB. Latent TB isn’t contagious, but active TB can make you and others sick.

How is tuberculosis diagnosed?

Skin test

Your doctor can use a purified protein derivative (PPD) skin test to determine if you are carrying the TB bacteria.

For this test, your doctor will inject 0.1 mL of PPD (a small amount of protein) under the top layer of your skin. After two to three days, you return to your doctor’s office. If there is a welt on your skin where the PPD was injected, you may be TB-positive. This test will tell you whether you have been exposed to TB; it does not tell you whether you have an active infection.  

However, the test isn’t perfect. Some people don’t respond to the test even if they have TB, and others respond to the test and don’t have TB. People who have recently received the TB vaccine may test positive but not have TB.

Chest X-ray

If your PPD test is positive, you will be sent for a chest X-ray, which checks for small spots in your lungs. These spots are a sign of TB infection and indicate that your body is trying to isolate TB bacteria. If your chest X-ray is negative, then either your PPD test was incorrect or you have latent TB. If it’s positive, then you should begin treatment for TB. If it’s negative, you will likely need to be treated for latent TB to prevent the bacteria from activating and making you sick later on.

Other tests

Your doctor may also order tests on your sputum or mucus, extracted from deep inside your lungs, to check for TB bacteria. If your sputum tests positive, this means you can infect others with the TB bacteria and should wear a special mask until after you have started treatment and your sputum tests negative for TB.

A blood test, called QuantiFERON-TB, is sometimes recommended to determine whether you have latent TB, but these tests may not be available in all areas. Like the skin test, this test can only tell if you have been exposed to the bacteria that cause TB. It cannot tell whether you have an active infection. The benefit of this test is that it does not give a false positive in people who have received the vaccine against TB. The limitation is that it may be falsely negative for a short time after initial exposure to TB. Like the skin test, it can occasionally give incorrect results (both positive and negative).

How is tuberculosis treated?

Many bacterial infections are treated with antibiotics for a week or two, but TB is different. People diagnosed with TB generally have to take one or more medications for six to nine months. The full treatment must be taken, otherwise it’s highly likely a TB infection could come back. If TB does recur, it may be resistant to previous medications.

Your doctor may prescribe multiple medications because some TB strains are resistant to certain drug types. The most common medications include:

High-dose antibiotics can harm your liver, so people taking TB medications should be aware of liver-injury symptoms, such as:

  • appetite loss
  • dark urine
  • fever lasting longer than three days
  • unexplained nausea or vomiting
  • jaundice, or yellowing of the skin

Notify your doctor immediately if you experience any of these symptoms. You should also have your liver numbers checked with frequent blood tests while taking these medications.

What is the outlook for tuberculosis?

Treatment for tuberculosis can be successful, given the person with the infection is healthy and has access to proper medical care.

If the infected person has other diseases, it can be harder to treat TB. For example, HIV and AIDS damage the immune system and weaken the body’s ability to fight off TB infection.

Other infections and diseases can complicate a TB infection, as can insufficient medical care. Generally, an early diagnosis and treatment, including a full course of antibiotics, offers the best chance for curing TB.

How can tuberculosis be prevented?

Most people in high-risk regions receive TB vaccinations as children. The vaccine is called Bacillus Calmette-Guerin, or BCG, and only protects against some TB strains. The vaccine isn’t commonly given in the United States.

Having the TB bacteria doesn’t necessarily mean you’ll have symptoms of active TB. If you do have the bacteria and don’t show symptoms, your doctor can prescribe preventive antibiotics to keep it from developing into active TB. A common medication for this is isoniazid, which must be taken for six to nine months to fully kill the bacteria.

People who have been diagnosed with TB should avoid crowds until they aren’t contagious. According to WHO, people with TB can infect 10 to 15 people through close contact per year if they don’t take precautions. People who are infected with TB can also wear a surgical mask, known as a respirator, to keep TB particles from spreading through the air. It’s best that a person with active TB avoid contact with others until finishing the first three to four weeks of treatment. 

Content licensed from:

Written by: Rachel Nall
Medically reviewed on: Jul 08, 2016: University of Illinois-Chicago, College of Medicine

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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