What is tuberculosis?

Tuberculosis (TB) is a contagious disease that can cause a serious infection, mainly affecting the lungs. Caused by the bacterium Mycobacterium tuberculosis, it can be potentially fatal if left untreated or not treated correctly. Some patients become very ill, while others never have symptoms. Most cases can be treated successfully with antibiotics, but they must be taken for many months to kill the bacteria. An active TB infection can cause coughing, fatigue, fever and weight loss, and is contagious. 

Are there different types of TB?

There are two types:

  • Latent TB infection means you have tuberculosis germs in your body. However, because of a healthy immune system, the body is able to stop the germs from growing. You don’t have symptoms or feel ill, and are not contagious. Unfortunately, the germs are still alive and they can become active at any time. This happens if your immune system is weakened and becomes less effective at fighting the germs. Latent TB infection requires medication to kill the bacteria and reduce your risk of later developing active TB disease. About 10% of infected people who fail to get treatment for latent TB infection will develop active TB disease at some point in their lives. If you have latent TB, your TB skin or blood test will be positive.
  • Active TB disease means TB germs are multiplying, you have symptoms, are ill, and you’re contagious. The majority of adult cases (90%) of active TB develop from latent TB infection. While it chiefly affects the lungs, TB can also affect many other parts of your body. Antibiotics are needed for six to 12 months to kill the bacteria and reduce the chances of infecting others.


What causes TB?

TB is caused by bacteria that are spread (by coughing, sneezing, talking) through the air from an infected person. Although it spreads via microscopic airborne droplets, like a cold or the flu, it is much harder to get. You must be around someone who has a lot of TB bacteria in their lungs for a lot of time, such as co-workers or family members. 

Once the bacteria are inhaled, they lodge in your lungs and start growing. If you have a healthy immune system, your body fights it and you won’t become ill or contagious to others. However, the bacteria will develop into active, contagious infection if your immune system is weak and unable to fight the infection. Active TB disease can happen within days or weeks in a patient with a weak immune system. Or, it can develop months or years later, when your immune system grows weaker. Your chances of quickly developing active TB are greater if your immune system is weak when you are first exposed. 

TB is hard to catch because TB germs cannot live on surfaces. You can’t get it by touching something the infected person has touched. It can’t be transmitted by shaking hands, sharing food or drink, or from faucets or toilets. Active TB patients are no longer contagious after they’ve had at least two weeks of treatment.

In the United States during the 1980s, TB cases increased rapidly because of the spread of HIV and AIDS. HIV is a virus that suppresses the immune system, making it harder for the body to fight off TB bacteria. HIV-positive patients have a high risk of getting active TB disease. They are also more likely to have latent TB progress to active TB.

Another fairly recent cause is the development of drug-resistant TB. Drugs used to treat it lose their ability to kill TB bacteria. Drug-resistant strains develop because patients don’t take their treatment medications correctly, or don’t complete the full course of treatment. When an antibiotic fails to kill all the bacteria it’s targeting, the surviving bacteria mutate and are able to resist antibiotics. 

TB is more likely to develop if you have certain risk factors. They include:

  • Weakened immune system that is caused by having HIV AIDS, diabetes, severe kidney disease, cancer or cancer treatment, anti-rejection drugs for an organ transplant, malnutrition or very low body weight, being very young or very old, or taking medications for rheumatoid arthritis, Crohn’s disease or psoriasis. 
  • Living in or traveling to areas with high TB rates, such as Africa, Asia, Caribbean, Eastern Europe, Russia or South America.
  • Alcohol or IV drug abuse
  • Smoking or using tobacco
  • Working in health care
  • Living or working in a residential care facility such as a prison, nursing home, or homeless shelter

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What are the symptoms of TB?

Latent TB infection does not cause any symptoms or sickness. 

Active TB disease in the lungs may cause these symptoms:

  • Coughing that lasts more than three weeks
  • Coughing up blood or mucus
  • Chest pain, especially when you breathe or cough
  • Fatigue
  • Night sweats
  • Fever and chills 
  • Loss of appetite and unintentional weight loss

TB can travel from your lungs, through your blood or lymph system, and affect other parts of the body. It can affect lymph nodes, bones, brain, spine, kidneys, and skin, causing symptoms related to that organ. For example, TB in your spine may cause back pain; in your kidneys it might cause blood in your urine. Unless TB is in the lungs, it’s usually not contagious. 


How is TB diagnosed?

TB is diagnosed with these tests:

  • Skin test (Mantoux tuberculin skin test) is done by injecting a small amount of fluid into the skin on your lower arm. After two to three days, you will be checked for swelling. A positive result means you have TB bacteria in your body. Accuracy of the skin test is reduced if you very recently got TB, or have had a TB vaccine (BCG).
  • Blood test (interferon-gamma release assays or IGRAs) requires a small amount of your blood to be mixed with TB proteins and the response is measured. 

If you get a positive test result, your doctor will need more testing to determine if you have active or latent TB. Additional testing is done by:

  • Chest X-ray or CT scan to look for changes in your lungs‍
  • Acid-fast bacillus (AFB) test looks for TB bacteria in your sputum (mucus coughed up from keep in your lungs)


How is TB treated?

A combination of antibiotics taken every day for at least six to 12 months will cure most active TB cases.

If you have active TB, you must have several weeks of antibiotic treatment before you’re not contagious. During the contagious period, you’ll need to take precautions to protect those around you. Precautions include:

  • Finish your medication! This is the most important thing you can do to keep from spreading the disease to those close to you. Failing to complete TB treatment is the main reason that dangerous drug-resistant TB bacteria are developing. Drug-resistant strains are deadlier. They are more difficult to treat, requiring the patient to take medications for up to 30 months, and they cause more side effects.  Both latent and active TB can be drug-resistant.
  • Stay home and stay away from family members. Don’t go to work or school, or sleep in the same room with anyone.
  • Increase ventilation in your sleeping room and room where you spend the day. Open the windows and use a fan to blow the room’s air to the outside.
  • Cover your mouth with a tissue every time you laugh, sneeze or cough. Dispose of the tissue in a sealed bag that is emptied regularly
  • Wear a face mask when you’re around others during the first three weeks of treatment.
  • Latent TB infections should be treated with medications that kill the bacteria so the infection doesn’t become active. You’ll need to take the medications for about nine months.

TB medication side effects can include upset stomach or nausea and vomiting, loss of appetite, weakness, chills, painful or swollen joints, lack of energy, muscle or joint pain.

Vaccination against TB is not recommended in the United States because it’s not very effective in adults. Infants are often given the BCG vaccine in less-developed countries where TB is more common. Currently, there are several TB vaccines in various stages of development and testing.


Mayo Clinic. (April 2021). Tuberculosis. Retrieved 8-18-21, {}
Centers for Disease Control and Prevention. (March 2016). Basic TB Facts. Retrieved 8-18-21, {}
WebMD. (June 2020). Tuberculosis (TB). Retrieved 8-18-21, {}
Medline Plus. (n.d.). Tuberculosis. Retrieved 7-18-21, {}


Medically reviewed by:

Dr. Javeed Siddiqui, MD, MPH

Dr. Siddiqui is the Chief Medical Officer at TeleMed2U responsible for clinical and technical program development as well as maintaining a thriving telemedicine practice in infectious diseases which includes specialized care of Hepatitis and HIV.

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