What is drug resistant TB?
A person has drug resistant TB if the TB bacteria that the person is infected with, will not respond to, which means that they are resistant to, at least one of the main TB drugs.1“Drug resistance” National Cancer Institute, http://www.cancer.gov
Drug susceptible TB is the opposite. If someone is infected with TB bacteria that are fully susceptible, it means that all of the TB drugs will be effective so long as they are taken properly. It still means that several drugs need to be taken together to provide effective TB treatment.
Drug susceptibility testing is how you find out which drugs will be effective against certain TB bacteria.
Is it possible to cure?
It is more difficult to cure TB which is drug resistant than TB which is fully susceptible, but it is still possible.
How do you get it?
There are two ways that people get it.
- Firstly, people get acquired drug resistant TB when their TB treatment is inadequate. This can be for a number of reasons, including the fact that patients fail to keep to proper TB treatment regimens. It can also be that the wrong TB drugs are prescribed, or sub standard TB drugs are used for treatment.
- Secondly, transmitted or primary drug resistant TB, results from the direct transmission of drug resistant TB from one person to another. The occurrence and prevention of primary drug resistant TB has largely been neglected during the development of global programs to end TB. It had been believed that most development of drug resistant TB arose from acquired TB.
New tools have enabled researchers to investigate this further. They have found that primary resistance plays a much greater role than previously thought.2"Report warns of rise in drug-resistant tuberculosis", 2017, http://www.cidrap.umn.edu/news-perspective/2017/03/report-warns-rise-drug-resistant-tuberculosis
Our best estimates are that globally, at least 75% to 80% of drug-resistant TB is now primarily transmitted, as opposed to primarily acquired during treatment. D Dowdy
So simply doing a better job of treating drug susceptible TB is no longer sufficient for controlling drug resistance. To control it, it is necessary to specifically diagnose and treat it.
What are the main types?
MDR (multi drug resistant) TB is the name given to TB when the bacteria that are causing it are resistant to at least isoniazid and rifampicin, two of the most effective TB drugs.
When a person is described as having MDR TB, it is not clear whether they may also be resistant to other drugs as well. So the World Health Organisation has now started to refer to “uncomplicated MRD TB”. This is TB which is resistant to isoniazid and rifampicin (making it MDR TB) but it is known that the bacteria are not resistant to any of the second line TB drugs.
XDR TB (extensively drug resistant TB) is defined as strains resistant to at least rifampicin and isoniazid. This is in addition to strains being resistant to one of the fluoroquinolones, as well as resistant to at least one of the second line injectable TB drugs amikacin, kanamycin or capreomycin.3“Extensively drug-resistant tuberculosis (XDR-TB): recommendations for prevention and control”, Weekly epidemiological record, WHO, 2006, www.who.int/
MDR TB and XDR TB do not respond to the standard six months of TB treatment with “first line” anti TB drugs. Treatment for them can often take two years or more and requires treatment with other drugs that are less potent, more toxic and much more expensive. However, there are now starting to be some shorter regimens for treatment, based on the Bangladesh regimen.
What other types are there?
A third type variously referred to as totally drug resistant TB, XXDR-TB or TDR-TB has also now been detected.4Velayati, Ali “Emergence of New Forms of Totally Drug Resistant Tuberculosis Bacilli”, Chest, Vol 136, August 2009, no. 2 420-425
http://www.ncbi.nlm.nih.gov/pubmed/ 5Migliori, G “125 years after Robert Koch’s discovery of the tubercle bacillus: the new XDR-TB threat. Is “science” enough to tackle the epidemic?”, European Respiratory Journal, March 1 2007
http://erj.ersjournals.com It is sometimes also referred to as extremely drug resistant TB. It is extremely difficult, although not always totally impossible to treat.
What are the statistics for MDR TB and XDR TB?
Globally, 186,772 cases of MDR TB or rifampicin resistant TB (MDR/RR TB) were detected and notified in 2018. This was an increase from 160,684 in 2017. 156,071 cases were enrolled in treatment. This was an increase from 139,114 in 2017.
Globally 13,068 cases of XDR-TB were notified in 2018.
However the number of people enrolled in treatment in 2018 was equivalent to only 32% of the estimated incidence of 484,000 cases.
The treatment outcome data from WHO gives success rates of 56% for MDR/RR-TB and 39% for extensively drug resistant TB.
Where do MDR TB and XDR TB occur?
The notified cases of MDR TB and XDR TB by World Health Organisation (WHO) region are given below.6“Global Tuberculosis Report 2019”, WHO, Geneva, 2019,
|Region||Cases of MDR/RR-TB TB||Cases of XDR-TB|
High burden countries
There is now a new list of 30 high burden MDR TB countries. The 30 “high burden” MDR TB countries are:
Angola, Azerbaijan, Bangladesh, Belarus, China, DPR Korea, DR Congo, Ethiopia, India, Indonesia, Kazakhstan, Kenya, Kyrgyzstan, Mozambique, Myanmar, Nigeria, Pakistan, Papua New Guinea, Peru, Philippines, Republic of Moldova, Russian Federation, Somalia, South Africa, Tajikistan, Thailand, Ukraine, Uzbekistan, Viet Nam, Zimbabwe.
There is more about high burden TB countries.
This page was last updated in February 2020.
Author Annabel Kanabus
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