by Dr. Jaclynn Moskow
Each year on March 24th, we recognize “World Tuberculosis Day” in an effort to build global awareness about the ongoing tuberculosis epidemic. Tuberculosis is an infectious disease caused by bacteria of the Mycobacterium tuberculosis complex, including Mycobacterium tuberculosis, Mycobacterium africanum, and Mycobacterium bovis (1). Worldwide, tuberculosis is the leading cause of death from an infectious agent (2).
“World Tuberculosis Day” occurs on March 24th as it was on this date, in 1884, that Dr. Robert Koch announced that he had discovered the causative agent of this disease (3).
Tuberculosis is generally spread via the inhalation of droplet nuclei expelled by individuals with the active pulmonary or laryngeal disease. Less commonly, humans may also acquire tuberculosis from consuming unpasteurized dairy products. The incubation period of tuberculosis ranges from 4w-12w.
Clinical manifestations of tuberculosis vary depending on the site of mycobacterial proliferation (4). Most infections represent reactivation of a dormant focus in a lung and present with chronic fever, weight loss, nocturnal diaphoresis, and productive cough (5). Approximately 8% of patients with pulmonary tuberculosis will experience hemoptysis (6). Tuberculosis can also cause extrapulmonary disease in sites including the bone, joints, muscles, central nervous system, gastrointestinal system, hepatobiliary system, genitourinary system, eyes, breasts, and skin.
Individuals with latent tuberculosis infection (LTBI) do not experience symptoms but are carriers of the disease. They cannot spread the disease to others unless it becomes reactivated. The lifetime risk of reactivation for a person with documented LTBI is estimated to be 5–10% (7). Immunocompromised individuals are much more likely to experience tuberculosis reactivation.
Diagnosis and Treatment
A definitive diagnosis of tuberculosis is made by the identification of the Mycobacterium tuberculosis complex in a clinical sample. Since the culture of these bacteria can be time-consuming, treatment may be initiated based on clinical suspicion alone. Tuberculosis skin tests and blood tests can be used to identify whether an individual has been infected, but cannot be used to distinguish between active and latent infections. Radiographic and other imaging techniques may also be useful in identifying patients, including those with asymptomatic active disease.
Typical pulmonary infection is treated with two months of Isoniazid, Rifampin, and Pyrazinamide (with Ethambutol pending results of susceptibility testing), followed by four months of Isoniazid and Rifampin alone. Treatment of multidrug-resistant tuberculosis generally includes the use of five drugs (including Pyrazinamide and/or Rifampin) for at least 6 months, followed by four drugs for 18-24 months (5).
Patients suspected of having active tuberculosis should be isolated, and healthcare personnel should observe relevant precautions.
The Centers for Disease Control and Prevention recommends treating individuals with latent tuberculosis that are at a high risk of progressing to an active infection. Included in the “high risk” designation are individuals with HIV/AIDS and other diseases that weaken the immune system, individuals who became infected with tuberculosis in the last two years, infants and young children, the elderly, and injecting drug users (8).
In 2018, approximately 1.7 billion individuals were infected with Mycobacterium tuberculosis – roughly 23% of the world’s population (9). In 2019, approximately 10 million individuals experienced symptomatic tuberculosis, and approximately 1.4 million died as a result of the disease (10). Tuberculosis is found worldwide, but over 95% of cases and deaths occur in developing countries (10). Eight countries currently account for two-thirds of new tuberculosis cases: India, Indonesia, China, Philippines, Pakistan, Nigeria, Bangladesh, and South Africa (10). If you have a GIDEON account, click here to explore our tuberculosis outbreak map.
Tuberculosis cases and rates Worldwide, 1965 – today
Currently, Bacille Calmette-Guerin (BCG) vaccine remains the only licensed vaccine for the prevention of tuberculosis. It provides some protection against childhood tuberculosis but is less effective in preventing adult disease (11). BCG is commonly given to children in countries in which tuberculosis is prevalent, and is estimated to decrease the risk of contracting the disease by 50% (12).
Prevention for High-Risk Travelers
The Centers for Disease Control and Prevention recommend that “travelers who anticipate possible prolonged exposure to people with tuberculosis (for example, those who expect to come in contact routinely with clinic, hospital, prison, or homeless shelter populations) should have a skin or blood test before leaving the United States. If the test reaction is negative, they should have a repeat test 8 to 10 weeks after returning to the United States. Additionally, annual testing may be recommended for those who anticipate repeated or prolonged exposure or an extended stay over a period of years.” (8)
In 2014, the World Health Organization announced that they seek to end the global tuberculosis epidemic by 2035. They defined this goal “with targets to reduce tuberculosis deaths by 95% and to cut new cases by 90%, and to ensure that no family is burdened with catastrophic expenses due to tuberculosis.” WHO called on the cooperation and collaboration of governments, and suggested a strategy that focuses on highly vulnerable populations (such as migrants) (13).
In 2020, they announced that the COVID-19 pandemic has stalled progress, as a result of resources being reallocated (2). They noted, for example, that many diagnostic testing machines have been used to test for COVID-19 instead of for tuberculosis. Hopefully, robust testing efforts for the disease will resume soon, as the identification of cases is critical to ending the epidemic.
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(1) M. Rowe and J. Donaghy, “Mycobacterium bovis: the importance of milk and dairy products as a cause of human tuberculosis in the UK. A review of taxonomy and culture methods, with particular reference to artisanal cheeses”, International Journal of Dairy Technology, vol. 61, no. 4, pp. 317-326, 2008. Available: 10.1111/j.1471-0307.2008.00433.x
(2) “Global Tuberculosis Report”, World Health Organization, 2020. [Online]. Available: https://apps.who.int/iris/bitstream/handle/10665/336069/9789240013131-eng.pdf
(3) “The Clock Is Ticking: World TB Day 2021”, World Health Organization, 2021. [Online]. Available: https://www.who.int/campaigns/world-tb-day/world-tb-day-2021
(4) W. Cruz-Knight and L. Blake-Gumbs, “Tuberculosis”, Primary Care: Clinics in Office Practice, vol. 40, no. 3, pp. 743-756, 2013. Available: 10.1016/j.pop.2013.06.003
(5) “Tuberculosis”, GIDEON Informatics, Inc, 2021. [Online]. Available: https://app.gideononline.com/explore/diseases/tuberculosis-12470
(6) U. Seedat and F. Seedat, “Post-primary pulmonary TB haemoptysis – When there is more than meets the eye”, Respiratory Medicine Case Reports, vol. 25, pp. 96-99, 2018. Available: 10.1016/j.rmcr.2018.07.006
(7) “Latent tuberculosis infection (LTBI): FAQs”, World Health Organization, 2021. [Online]. Available: https://www.who.int/tb/areas-of-work/preventive-care/ltbi/faqs/en/
(8) “Tuberculosis: Basic TB Facts: TB Prevention”, Centers for Disease Control and Prevention, Division of Tuberculosis Elimination, 2016. [Online]. Available: https://www.cdc.gov/tb/topic/basics/tbprevention.htm
(9) “Global Health: Newsrooms: Global Health Topics: Tuberculosis”, Centers for Disease Control and Prevention, Global Health, 2020. [Online]. Available: https://www.cdc.gov/globalhealth/newsroom/topics/tb/index.html
(10) “Tuberculosis: Key Facts”, World Health Organization, 2020. [Online]. Available: https://www.who.int/news-room/fact-sheets/detail/tuberculosis
(11) S. Fatima, A. Kumari, G. Das, and V. Dwivedi, “Tuberculosis vaccine: A journey from BCG to present”, Life Sciences, vol. 252, p. 117594, 2020. Available: 10.1016/j.lfs.2020.117594
(12) G. Colditz, “Efficacy of BCG Vaccine in the Prevention of Tuberculosis”, JAMA, vol. 271, no. 9, p. 698, 1994. Available: 10.1001/jama.1994.03510330076038
(13) “WHO End TB Strategy”, World Health Organization, 2021. [Online]. Available: https://www.who.int/tb/post2015_strategy/en/