TB bacteria are most commonly found in the lungs. They can, however, spread to other parts of the body, in which case the symptoms would be localised in those areas. LTBI has no symptoms. Common symptoms of TB disease in the lungs include19:
A bad cough that lasts 3 weeks or longer
Pain in the chest
Coughing up blood or sputum (phlegm from deep inside the lungs)
Weakness or fatigue
Loss of appetite
Exposure to TB occurs when you have spent time with someone who is infected with active TB disease. The bacteria are spread through the air when a person who has active TB sneezes, coughs or speaks. If you think you have been exposed to active TB, you should immediately contact your doctor or the local public health department20.
Learning about TB and the risk factors for TB is important, as there are several different factors that can make a person susceptible to TB. However, these risk factors usually fall into two categories21:
Being in close contact with someone who has been recently infected with TB
Having a medical condition that weakens the immune system
1. Close proximity
The chances of a person getting infected with TB are higher for people that are in close contact with others who are infected. This includes21:
Family and friends of a person with TB
People who come from areas of the world with high TB rates
People in groups with high rates of TB transmission – such as the homeless, injection drug users or a person with HIV
People who work or reside in a place where the people are at a high-risk for TB – such as hospitals, homeless shelters, correctional facilities or nursing homes
People receiving certain specialised treatment for autoimmune diseases
Overall, 5-10% of people with latent TB who don’t receive treatment will develop active TB disease at some point in their lives.1
There are two categories of commercially available tests to detect TB infection:
Tuberculin skin test (TST)
The TST has been used to detect TB infection for over 100 years. It requires an intradermal injection of a small amount of purified protein derivative (PPD), a TB antigen, into the skin. In 48 – 72 hours, the resultant induration is measured22.
Tuberculin is injected into the skin on the lower part of the arm
Subject returns 48 to 72 hours later to have their test “read” to determine whether there has been a reaction to the tuberculin
Limited sensitivity, especially in the immunocompromised, young and elderly
Poor specificity; caused by:
Prior bacille Calmette–Guérin (BCG) vaccination
Non-tuberculosis mycobacteria (NTM) infection
Requires 2 visits
Failure to return for second visit = no test result
Administration and interpretation steps are technique-dependent
Interferon-gamma release assays (IGRAs)
Three IGRAs currently approved by the FDA for use as an aid in diagnosing TB are: the T-SPOT.TB test, the multi-tube ELISA test and the Chemiluminescence immunoassay (CLIA). These tests each involve a blood draw, which is then processed by a lab.
People with active TB disease must be treated and must take all of their medication exactly as directed. If they do not do this, the TB bacteria can become resistant to the drugs used to treat it. A typical course of treatment for active TB lasts from 6 – 9 months23.
It is is important to remember that TB is contagious and can be spread by an infected person coughing. For this reason, TB treatment often involves a period of isolation.
Lewinsohn DM, Leonard MK, LoBue PA, et al. Official American ThoracicSociety/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children. Clin Infect Dis. Published online December 8, 2016:ciw694. doi:10.1093/cid/ciw694
Wong SH, Gao Q, Tsoi KKF, et al. Effect of immunosuppressive therapy on interferon γ release assay for latent tuberculosis screening in patients with autoimmune diseases: a systematic review and meta-analysis. Thorax. 2016;71:64–72.
Mazurek GH, Jereb J, Vernon A, LoBue P, Goldberg S, Castro K, IGRA Expert Committee, Centers for Disease Control and Prevention (CDC). Updated guidelines for using Interferon Gamma Release Assays to detect Mycobacterium tuberculosis infection – United States, 2010. MMWR Recomm Rep. 2010; 59(RR-5:1-25.
WHO End TB Strategy. World Health Organization. Published September 8, 2015. Accessed November 12, 2020.
Wrighton-Smith P, Sneed L, Humphrey F, Tao X, Bernacki E. Screening health care workers with interferon-γ release assay versus tuberculin skin test: Impact on costs and adherence to testing (the SWITCH study). J Occupational & Environmental Med. 2012;54(7):806-815
GBD 2017 Inflammatory Bowel Disease Collaborators. The global, regional, and national burden of inflammatory bowel disease in 195 countries and territories, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017. The Lancet Gastroenterology & Hepatology. 2020;5(1):17-30
Lai CC, Tan CK, et al. Diagnostic performance of whole-blood interferon-γ assay and enzyme-linked immunospot assay for active tuberculosis. J Microbiol Immunol Infect. 2011 Oct;44(5):406-7. doi: 10.1016/j.jmii.2011.07.002. Epub 2011 Sep 8.
Redelman-Sidi G, Sepkowitz KA. Interferon-gamma release assays in the diagnosis of latent tuberculosis infection among immunocompromised adults. Am J Respir Crit Care Med 2013; 188:422-431. 2012/12/25. DOI: 10.1164/rccm.201209-1621CI.
Exposure to TB. Centers for Disease Control and Prevention. CDC Exposure to TB. Published March 21, 2016. Accessed January 8, 2020.
TB Risk Factors. Centers for Disease Control and Prevention. CDC TB Risk Factors. Published March 18, 2016. Accessed January 8, 2020.
Huebner R, Schein M, Bass J. The tuberculin skin test. Clin Infect Dis. 1993;968-975.
Treatment for TB Disease. Centers for Disease Control and Prevention. CDC Treatment for TB Disease. Published April 5, 2016. Accessed January 8, 2020.
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