Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis and it most often affects the lungs, but TB bacteria can also attack any part of the body such as the kidney, spine, and brain.1,2

Difference Between Tuberculosis Infection and Tuberculosis Disease

Not everyone infected with TB bacteria becomes sick. There are two TB-related conditions Latent TB infection and TB disease. People with latent TB infection have no symptoms, may have a positive TB skin test reaction or positive TB blood test, and can develop TB disease if do not receive appropriate treatment. The person with TB disease usually feels sick, have symptoms, can spread TB bacteria to others & both skin tests and blood tests usually appear positive.1

Spread of Tuberculosis

Tuberculosis spreads through the air. When a person with TB disease coughs, sneezes speaks or sings the bacteria is put into the air. The bacteria can stay in the air for several hours depending on the environment. Prolonged exposure to tuberculosis is normally necessary for infection to occur. People with TB infection are not able to transmit it to others.1

Sign and symptoms of TB

People with TB infection do not show any signs and symptoms and do not feel sick. People who develop TB disease have a variety of symptoms depending on where in the body the TB bacteria are present and growing. Mostly, TB bacteria grow in the lungs and symptoms include a bad cough for 3 weeks or longer, chest pain, coughing up blood in sputum, excessive weakness/fatigue, noticeable weight loss, frequent chills, fever, and regular night sweats.1,3

Tuberculosis: A Global Threat

Tuberculosis remains a major health problem worldwide, with at least three million deaths annually. Each year there are nearly 10 million new cases, of which four to five million are smear-positive and, thus, highly contagious.2,4
The World Health Organization (WHO)- 2020 report states that Tuberculosis is the 13th leading cause of death and a second-leading infectious killer after Covid- 19. Moreover, 8 countries accounted for 2/3rd of the total new TB cases, globally; wherein India accounts for the maximum cases followed by China, Indonesia, Philippines, Pakistan, Nigeria, Bangladesh & South Africa.2,3

Risk of TB

Tuberculosis mostly affects adults. However, all age groups are at risk. Over 95% of cases and deaths are in developing countries. As per the WHO report, people with HIV are 18 times more likely to develop active TB. The risk of active TB is also greater in persons suffering from other conditions that impair the immune system. People with undernutrition are 3 times more at risk. Globally in 2020, there were 1.9 million new TB cases that were attributable to undernutrition.2,3 Alcohol use disorder and tobacco smoking increase the risk of TB disease by a factor of 3.3 and 1.6, respectively. In 2020, 0.74 million new TB cases worldwide were attributable to alcohol use disorder and 0.73 million were attributable to smoking.2,3

Diagnosis of TB

Test for TB Infection

The Mantoux tuberculin skin test (TST) or the TB blood test can be used to test for M. tuberculosis infection. This Mantoux tuberculin skin test is performed by injecting a small amount of fluid called tuberculin into the skin in the lower part of the arm. The test is read within 48 to 72 hours by a qualified health care professional, who looks for a reaction (induration) on the arm.5

Diagnostic Microbiology

The presence of acid-fast-bacilli (AFB) on a sputum smear or other specimen often indicates the presence of the TB disease. Acid-fast microscopy is easy and quick, but it does not confirm the diagnosis of TB because some acid-fast-bacilli are not M. tuberculosis.5

Therefore, a culture is done on all initial samples to confirm the diagnosis. A positive culture for M. tuberculosis confirms the diagnosis of TB disease.5
Culture examinations should be completed on all specimens, regardless of AFB smear results. Laboratories should report positive results on smears and cultures within 24 hours by telephone or fax to the primary health care provider and to the state or local TB control program, as required by law. The TB blood test measures the patient’s immune system reaction to M. tuberculosis.2,5

Dr. Dangs Lab TB Test Panels

Diagnostic tests

  • Rapid AFB Smear and Culture
  • GeneXpert MTB/RIF Ultra assay (RT-PCR)
  • Fine Needle Aspiration Cytology
  • Mantoux tuberculin skin test (TST)
  • TB Blood test (Interferon-Gamma Releasing Assays (IGRAs))

MDR-TB diagnostic technology

  • MOLECULAR DST (Eg. GeneXpert or Line probe assay (LPA))

Tuberculosis (TB) is caused by a bacteria called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain. Not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions exist- latent TB infection (LTBI) and TB disease. If not treated properly, TB disease can be fatal.
Publisher’s name- Dr. Dangs Lab

References :
  1. CDC/24 7. Tuberculosis (TB), accessed on 5/11/2021. Available at
  2. Tuberculosis, accessed on 5/11/2021. Available at
  3. Tuberculosis, on 5/11/2021. Available at
  4. Hirschfield ES. Tuberculosis - Still a major health problem. Can J Infect Dis. 1991;2(4):131-132. doi:10.1155/1991/297605.
  5. Diagnosis of Tuberculosis Disease, accessed on 8/12/2021. Available at

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion.

Related Articles
  1. Shingadia D. The diagnosis of tuberculosis. Pediatr Infect Dis J. 2012 Mar;31(3):302-5. doi: 10.1097/INF.0b013e318249f26d. PMID: 22330167.
  2. Suárez I, Fünger SM, Kröger S, Rademacher J, Fätkenheuer G, Rybniker J. The Diagnosis and Treatment of Tuberculosis. Dtsch Arztebl Int. 2019 Oct 25;116(43):729-735. doi: 10.3238/arztebl.2019.0729. PMID: 31755407.
  3. MacLean E., Kohli M, Weber SF, et al. Advances in Molecular Diagnosis of Tuberculosis. Journal of Clinical Microbiology. 2020; 58 (10): e01582-19. doi = {10.1128/JCM.01582-19}