Multidrug-resistant tuberculosis

Multidrug-resistance tuberculosis
Mycobacterium tuberculosis bacteria seen by microscope
Specialty	Infectious disease

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Multidrug-resistant tuberculosis (MDR-TB) is a form of tuberculosis (TB) infection caused by bacteria that are resistant to treatment with at least two of the most powerful first-line anti-TB medications (drugs): isoniazid and rifampicin. Some forms of TB are also resistant to second-line medications, and are called extensively drug-resistant TB (XDR-TB).^[1]

Tuberculosis is caused by infection with the bacterium Mycobacterium tuberculosis. Almost one in four people in the world are infected with TB bacteria.^[1] Only when the bacteria become active do people become ill with TB. Bacteria become active as a result of anything that can reduce the person's immunity, such as HIV, advancing age, diabetes or other immunocompromising illnesses. TB can usually be treated with a course of four standard, or first-line, anti-TB drugs (i.e., isoniazid, rifampicin, pyrazinamide and ethambutol).^[2][3]

However, beginning with the first antibiotic treatment for TB in 1943, some strains of the TB bacteria developed resistance to the standard drugs through genetic changes (see mechanisms.)^[2][4][5] This process accelerates if incorrect or inadequate treatments are used, leading to the development and spread of multidrug-resistant TB (MDR-TB). Incorrect or inadequate treatment may be due to use of the wrong medications, use of only one medication (standard treatment is at least two drugs), or not taking medication consistently or for the full treatment period (treatment is required for several months).^[6][7][8]

Treatment of MDR-TB requires treatment with second-line drugs, (i.e., fluoroquinolones, aminoglycosides, and others), which in general are less effective, more toxic and much more expensive than first-line drugs.^[6] Treatment regimes can run for two years, compared to the six months of first-line drug treatment.^[9][7] If these second-line drugs are prescribed or taken incorrectly, further resistance can develop leading to XDR-TB.^{[citation needed]}

MDR-TB can be directly transmitted from an infected person to an uninfected person. In this case a previously untreated person develops a new case of MDR-TB. This is known as primary MDR-TB, and is responsible for up to 75% of cases.^[10] Acquired MDR-TB develops when a person with a non-resistant strain of TB is treated inadequately, resulting in the development of antibiotic resistance in the TB bacteria infecting them. These people can in turn infect other people with MDR-TB.^[5][6]

MDR-TB caused an estimated 600,000 new TB cases and 240,000 deaths in 2016 and MDR-TB accounts for 4.1% of all new TB cases and 19% of previously treated cases worldwide.^[11] Globally, most MDR-TB cases occur in South America, Southern Africa, India, China, and the former Soviet Union.^[12]