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Tuberculosis (TB)

Last updated Feb. 17, 2018

Approved by: Maulik P. Purohit MD, MPH

Tuberculosis (TB) is a contagious infection caused by the bacterium Mycobacterium tuberculosis.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Koch's Disease
  • MTB (Mycobacterium Tuberculosis Infection)
  • TB (Tuberculosis)

What is Tuberculosis? (Definition/Background Information)

  • Tuberculosis (TB) is a contagious infection caused by the bacterium Mycobacterium tuberculosis. The disease is characterized by the formation of nodules (tubercles) in the affected tissues, from which the name is derived
  • The infection occurs in people worldwide, without any racial or gender bias; with fewer cases occurring in developed countries, when compared to the underdeveloped or developing countries
  • Compromised immunity due to age or disease, malnutrition, living in unsanitary conditions, poverty, and some pre-existing health conditions are risk factors for being diagnosed with Tuberculosis
  • The infection spreads primarily through air, when an infected individual sneezes, coughs, or even sings or speaks. This action causes the release of bacteria into air. All individuals, who breathe the contaminated air, can become infected with Tuberculosis
  • The infection normally affects the lungs (when it is called pulmonary Tuberculosis), but other parts of the body may be affected as well. Individuals are most likely to contract the condition from family members, friends, and co-workers
  • A persistent cough that lasts for over 3 weeks is a key symptom of Tuberculosis. However, an infected individual may also experience fever, chills, fatigue, wheezing, and night sweats
  • A preliminary diagnosis of Tuberculosis is made with the aid of a complete physical examination, assessment of symptoms, an individual’s medical history, and a TB skin test. A positive skin test is indicative of an infection with the bacterium. A follow-up with X-ray of the chest and microbial cultures of the sputum is generally undertaken to confirm an active or latent TB
  • The treatment measures differ slightly for latent and active Tuberculosis infections. Even though the same set of medications are typically prescribed in both cases, individuals with active forms of the disease may have to take multiple antibiotics  for a longer period of time to completely eliminate the bacterium from the body
  • The prognosis of Tuberculosis is generally good, if infected individuals take the full-course of prescribed medications for the recommended time period. However, if the condition is left untreated, TB can prove to be fatal

Who gets Tuberculosis? (Age and Sex Distribution)

  • Tuberculosis is a potentially fatal disease occurring worldwide, affecting all races and ethnic groups
  • It can infect any individual, of any age (particularly, if they have a weak immune system). Although statistically, young adults are amongst the most affected individuals
  • Both genders (males and females) are equally at risk
  • TB is common in Asia (India, China, and Indonesia), Africa (specifically sub-Saharan Africa, including Nigeria, Congo, and South Africa), and some South American countries. The infections are fewer in developed countries, such as Australia, Europe, and the USA

What are the Risk Factors for Tuberculosis? (Predisposing Factors)

The risk factors for Tuberculosis may include:

  • HIV infection (TB is the leading cause of death in HIV-infected individuals)
  • Previous TB infection; within the last 2 years
  • The presence of other health conditions/diseases that make it difficult for the body to fight a bacterial infection (such as diabetes)
  • Drug and alcohol abuse
  • Elderly adults with weak immune system
  • Poverty, poor standards of living, and overcrowding conditions/settlements
  • Malnutrition, especially among children
  • Prolonged stress can weaken the immune system increasing the risk
  • Use of medication that can suppress the immune system (such as corticosteroids and infliximab)

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Tuberculosis? (Etiology)

  • Tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis (a rod-shaped bacterium)
  • The infection usually occurs in the lung, but can also occur in other areas of the body; it is a multi-system disease
  • The infection is usually transmitted from one infected individual to another via contaminated air (through respiratory droplets)

What are the Signs and Symptoms of Tuberculosis?

The signs and symptoms of Tuberculosis may include:

  • A persistent cough that lasts for 3 weeks or longer
  • Breathlessness
  • Swollen lymph nodes
  • Chest pain
  • Pain during breathing
  • Fatigue
  • A general feeling of being sick
  • Weight loss and lack of appetite
  • Night sweats
  • Fever and chills
  • Coughing-up phlegm and/or blood
  • Wheezing 

How is Tuberculosis Diagnosed?

The diagnosis of Tuberculosis is made through the following tests and exams:

  • A thorough physical exam, which may reveal the following:
    • Clubbed fingers or toes
    • Inflammation of the lymph nodes in the neck region
    • Unusual sounds while breathing
    • Increased fluid in the lung area
  • An assessment of symptoms
  • Evaluation of medical history
  • The TB skin test, also known as purified protein derivative (PPD) test or tuberculin test
    • The skin test involves an injection of a small amount of tuberculin (which contains the tuberculosis bacteria) into the lower arm
    • 48-72 hours after the injection, a healthcare provider examines the site of injection
    • If there is swelling in the area, the test is positive and it indicates that the individual is infected with Mycobacterium tuberculosis
    • If no swelling is noted, the test is negative and the individual is not infected
  • TB screening blood test, also called interferon-gamma release assay or IGRA:
    • A blood sample is collected and tested, to see how the individual’s immune system responds to the tuberculosis bacteria
    • Like the TB skin test, a positive test indicates the presence of TB bacteria in the individual; a negative test indicates that there is no infection
  • If the blood or skin TB test is positive, follow-up tests are conducted to confirm latent or active infection:
    • Chest X-rays and other imaging studies such as a chest CT scan
    • Sputum culture
    • Blood culture
    • Advanced molecular testing on sputum or blood specimen
    • Bronchoscopy: A technique for visualizing the insides of the airways for diagnostic purposes

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Tuberculosis?

Some possible complications of Tuberculosis may include:

  • Significant blood loss, via coughing-up blood
  • Infection with multi-drug resistant Tuberculosis strain (owing to inadequate or improper medication regimen)
  • TB infection in body parts other than the lungs (usually associated with HIV-positive individuals)
  • Meningitis brought on by TB (more common in children)
  • Collapsed lung
  • Permanent lung damage

If untreated, Tuberculosis is a fatal condition.

How is Tuberculosis Treated?

The treatment for Tuberculosis is based on whether the affected individual has a latent or an active TB infection:

  • The treatment for TB infection involves the use of antibiotics to destroy the bacteria causing the infection. The treatment regimen may vary between latent and active infections. Whereas both are treated with antibiotics, an active TB disease may require a combination of drugs for a longer time period to completely rid the body of the pathogen. The type of medication, dosage, combination of drugs and duration of treatment are determined by the healthcare provider, based upon each individual’s particular health condition and other factors (such as age, pre-existing medical conditions, etc.)
  • Directly observed therapy (DOT):  Here, the treatment is directly supervised by a healthcare provider, who provides each dose of the prescribed (oral) medication, and ensures that it is swallowed by the patient (this may even be on a daily basis). The WHO recommends DOTS (directly observed treatment, short-course) as the best and complete curative method for TB infection
  • It is extremely important to take the full regimen of medications, so that the bacteria may be eliminated from an individual’s body. Otherwise, the infection may linger and become active later on.

Additionally, inappropriate or insufficient treatment can lead to the development of multidrug resistant forms of the TB-causing bacterium.

  • A multidrug resistant Tuberculosis (MDR-TB) develops when:
    • The prescribed drug course/regimen is not followed properly
    • The drugs being used have not been formulated properly, or are of poor quality
    • Improper storage of drugs takes place, such that their efficiency is compromised
    • Stopping drugs prematurely when the symptoms improve, without regard for the prescribed treatment duration
  • The MDR-TB is resistant to at least 2 of the most effective drugs to treat the disease. This form of disease is more difficult to treat
  • A form of disease known as extreme drug-resistant TB (XDR-TB) may develop when the bacterium develops resistance to several of the most effective drugs against TB

How can Tuberculosis be Prevented?

The following are the methods to help prevent getting infected by Mycobacterium tuberculosis, the bacterium that causes Tuberculosis:

  • Avoid contact with infected individuals, especially in closed and crowded areas. If such a contact is unavoidable, then proper respiratory protective equipment, such as a mask, should be used
  • Getting vaccinated against TB - vaccines called Bacilli Calmette-Guerin (BCG) are available against the disease. However, the effectiveness of the vaccine is currently being debated upon. BCG has been shown to reduce the rate of tuberculosis in children in developing countries
  • Getting treated once an individual has come into active contact with TB-infected individuals (i.e., those having confirmed tuberculosis infection)
  • Healthcare workers and individuals in close contact with the TB patients should follow strict hygiene and preventative measures
  • Getting treatment for any underlying medical condition(s) that may decrease immunity in the individual, such as by seeking suitable medical attention for maintaining good glycemic index in those with diabetes

Regular medical screening at periodic intervals with tests, and physical examinations are crucial, and highly recommended (for prevention and early diagnosis).

What is the Prognosis of Tuberculosis? (Outcomes/Resolutions)

  • The prognosis of Tuberculosis infection is good with treatment using medications, which are taken regularly and for the entire length of the prescribed period. The symptoms start to subside, typically with 2-3 weeks of treatment
  • Without proper treatment, the infection may worsen and spread from the lungs to other body parts, and evolve into disseminated disease. Complications arising from untreated disease may be fatal
  • In individuals with HIV infection and other conditions that weaken the immune system, the prognosis depends on many factors and is usually guarded

Additional and Relevant Useful Information for Tuberculosis:

  • Tuberculosis is a deadly disease worldwide. In 2015, according to US Centers of Disease Control and Prevention, approximately 10.4 million individuals contracted TB, of which 1.8 million succumbed to the disease
  • In many geographical (tropical) regions of the world (mainly in the lesser industrialized nations), where the healthcare system lacks the kind of preparation and resources needed to treat the disease, the mortality rates due to TB infection is very high
  • The evolution of multi-drug resistant tuberculosis (MDR-TB) is a significant public health concern around the world

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: July 20, 2014
Last updated: Feb. 17, 2018