Tuberculosis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Tuberculosis (abbreviated as TB for 'Tubercle bacillus' or Tuberculosis) is a common and deadly infectious disease caused by mycobacteria, mainly Mycobacterium tuberculosis. Tuberculosis most commonly attacks the lungs (as pulmonary TB) but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, joints and even the skin. Other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, and Mycobacterium microti can also cause tuberculosis, but these species do not usually infect healthy adults.[1] Over one-third of the world's population has been exposed to the TB bacterium, and new infections occur at a rate of one per second.[2] Not everyone infected develops the full-blown disease; asymptomatic, latent TB infection is most common. However, one in ten latent infections will progress to active TB disease, which, if left untreated, kills more than half of its victims.
Historical Perspective
Tuberculosis has been present in humans since antiquity. The earliest unambiguous detection of Mycobacterium tuberculosis was in the remains of bison, dated 18,000 BC.[3] However, whether tuberculosis originated in cattle and then transferred to humans, or diverged from a common ancestor, is currently unclear.[4] Through history tuberculosis had many names, such as phthisis and Wasting disease, which were mostly derived from its symptoms. The Mycobacterium tuberculosis was only identified in 1882 by Robert Koch. In the 19th and early 20th centuries, tuberculosis caused the most widespread public concern, being considered an endemic disease of the urban poor. It was only in 1946, with the development of the antibiotic streptomycin, that effective treatment and cure became possible. Since the rise of drug-resistant strains in the 1980s, hopes that the disease could be completely eliminated have been dashed.
Classification
Tuberculosis may be classified according to its pathogenesis into 6 categories. This classification divides patients from "class 0", in which the person hasn't had previous exposure to TB, and has a negative TST and IGRA, to "class 5", in which TB is suspected, there are signs and symptoms of the disease, but the evaluation is not complete to confirm the diagnosis. According to the U.S. Citizenship and Immigration Services, immigrants and refugees have a special classification system. This last classifies immigrants and refugees from "no class", in which the person has normal screening tests, to "class B3", in which the person is a recent contact of a known tuberculosis case.
Pathophysiology
About 90% of those infected with Mycobacterium tuberculosis have asymptomatic, latent TB infection (sometimes called LTBI), with only a 10% lifetime chance that a latent infection will progress to TB disease. However, if untreated, the death rate for these active TB cases is more than 50%.[5]
Causes
The primary cause of tuberculosis is Mycobacterium tuberculosis, an aerobic bacterium.
Epidemiology and Demographics
Tuberculosis, or TB is a bacterial infection that kills 3 million people worldwide, more people than any other infection in the world. Approximately one-third of the world is infected, and 15 million people in the US. Active tuberculosis kills 60% of the time if not treated, but treatment cures 90% of patients. Most people are infected with TB have latent TB. This means that the bacteria is controlled by the body's immune system. People with latent TB do not have symptoms and cannot transmit TB to other people. However, later if the infected person has a weakened immune system (AIDS, young children, elderly, sick with other diseases, etc.), the bacteria can break out leading to active TB, or TB disease.
Risk Factors
Progression from TB infection to TB disease occurs when the TB bacilli overcome the immune system defenses and begin to multiply.
Diagnosis
History and Symptoms
Tuberculosis can be a difficult disease to diagnose, due mainly to the difficulty in culturing this slow-growing organism in the laboratory. A complete medical evaluation for TB must include a medical history, a chest x-ray, and a physical examination.
Physical Examination
A physical exam can provide valuable information about the patient’s overall condition and other factors that may affect how TB is treated, such as HIV infection or other illnesses.
Electrocardiogram
Patients can develop a pericardial effusion secondary to TB and this might be manifested as low voltage and tachycardia on an EKG.
Chest X-Ray
A chest X ray is one of the important diagnostic tools in tuberculosis. A chest radiograph may be used to rule out the possibility of pulmonary TB in a person who are symptomatic or had a positive reaction to a tuberculin test or QFT-G and no symptoms of disease. The findings on chest x ray can be divided into parenchymal and pleural. The early parenchmal findings can be infiltrates, and cavity. A healed tuberculotic lesion can present as fibrosis, and calcification. Pleural lesions in form of pleral effusion can also be seen. An advanced tuberculosis lesion can present as combination of these early lesions and termed as fibrocavitatory lesions.
Echocardiography or Ultrasound
Echocardiography or ultrasound: Patients can develop a pericardial effusion secondary to TB.
Other Diagnostic Studies
Because of difficulties with the Tuberculin skin test, many laboratory methods of diagnosis are emerging [6] [7].
Treatment
Medical Therapy
If there is a high probability of infection, presumptively treat the patient even if the stain is negative, while waiting for the culture results. The patient should be brought back in few weeks. Patients usually feel better a few weeks post-treatment. In the U.S., all TB is tested for drug resistance. Isoniazid (INH) resistant TB can be treated in same way as non-MDR TB.
Surgery
Surgery may be necessary, especially to drain spinal abscesses or to stabilize the spine in case of Pott's disease.
Primary Prevention
Many countries use BCG vaccine as part of their TB control programs, especially for infants. This was the first vaccine for TB and developed at the Pasteur Institute in France between 1905 and 1921.[8] However, mass vaccination with BCG did not start until after World War II.[9] The protective efficacy of BCG for preventing serious forms of TB (e.g. meningitis) in children is greater than 80%; its protective efficacy for preventing pulmonary TB in adolescents and adults is variable, ranging from 0 to 80%.[10]
Secondary Prevention
All health-care settings need an infection-control program designed to ensure prompt 1) detection, 2) airborne precautions and 3) treatment of persons who have suspected or confirmed tuberculosis (TB) disease (or prompt referral of persons who have suspected TB disease for settings where persons with TB disease are not expected to be encountered). In order to be effective, the primary emphasis of the TB infection-control program should be on achieving these three goals.
In all health-care settings, particularly those in which persons who are at high risk for exposure to Mycobacterium tuberculosis work or receive care, policies and procedures for TB control should be developed, reviewed periodically, and evaluated for effectiveness to determine the actions necessary to minimize the risk for transmission of M. tuberculosis.
References
- ↑ Raviglione MC, O'Brien RJ (2004). "Tuberculosis". In Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL, Isselbacher KJ, eds. Harrison's Principles of Internal Medicine (16th ed. ed.). McGraw-Hill Professional. pp. 953–66. doi:10.1036/0071402357. ISBN 0071402357.
- ↑ World Health Organization (WHO). Tuberculosis Fact sheet N°104 - Global and regional incidence. March 2006, Retrieved on 6 October 2006.
- ↑ Rothschild B, Martin L, Lev G, Bercovier H, Bar-Gal G, Greenblatt C, Donoghue H, Spigelman M, Brittain D (2001). "Mycobacterium tuberculosis complex DNA from an extinct bison dated 17,000 years before the present". Clin Infect Dis. 33 (3): 305–11. PMID 11438894.
- ↑ Pearce-Duvet J (2006). "The origin of human pathogens: evaluating the role of agriculture and domestic animals in the evolution of human disease". Biol Rev Camb Philos Soc. 81 (3): 369–82. PMID 16672105.
- ↑ Onyebujoh, Phillip and Rook, Graham A. W. World Health Organization Disease Watch: Focus: Tuberculosis. December 2004. Accessed 07 October 2006.
- ↑ Drobniewski F, Caws M, Gibson A, Young D (2003). "Modern laboratory diagnosis of tuberculosis". Lancet Infect Dis. 3 (3): 141–7. PMID 12614730.
- ↑ Dinnes J, Deeks J, Kunst H, Gibson A, Cummins E, Waugh N, Drobniewski F, Lalvani A (2007). "A systematic review of rapid diagnostic tests for the detection of tuberculosis infection". Health Technol Assess. 11 (3): 1–314. PMID 17266837.
- ↑ Bonah C (2005). "The 'experimental stable' of the BCG vaccine: safety, efficacy, proof, and standards, 1921–1933". Stud Hist Philos Biol Biomed Sci. 36 (4): 696–721. PMID 16337557.
- ↑ Comstock G (1994). "The International Tuberculosis Campaign: a pioneering venture in mass vaccination and research". Clin Infect Dis. 19 (3): 528–40. PMID 7811874.
- ↑ Bannon M (1999). "BCG and tuberculosis". Arch Dis Child. 80 (1): 80–3. PMID 10325767.