Multi drug-resistant tuberculosis (MDR-TB) is a strain of TB bacteria that has become resistant to TB drugs.
MDR-TB is difficult and costly to treat, and can be fatal.
The current definition of MDR-TB is when a strain of TB is resistant to at least two first-line anti-TB drugs.
Extensive Drug Resistant TB (XDR-TB also) is defined as MDR-TB that has also become resistant to three or more second-line drugs.
Drug resistance is caused by TB patients failing to complete treatment regimens or receiving incorrect treatment.
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What is multi drug-resistant TB?
Bacterial TB strains resistant to an anti-TB drug or a combination of these have emerged.
The current definition of multi drug-resistant TB (MDR-TB) is when bacteria become resistant to at least two first-line therapies - the drugs isoniazid and rifampin, considered to be the most potent against the disease.
What is XDR-TB?
XDR-TB stands for Extensive drug-resistant TB (also referred to as Extreme drug-resistance). This is a newly identified TB threat: MDR-TB that has also become resistant to three or more of the six classes of reserve second-line drugs.
This description of XDR-TB was first used earlier in 2006, after a survey by the World Health Organization (WHO) and the US Centres for Disease Control (CDC) and Prevention.
The emergence of XDR-TB is cause for great concern because it is widely distributed geographically, and renders patients virtually untreatable with available drugs.
A survey conducted by the WHO and CDC found that XDR-TB has been identified in all regions of the world but is most frequent in the former Soviet Union and Asia.
The medical community considers XDR-TB to be a major public health threat associated with high mortality rates, especially in areas with high HIV rates and poor health care resources. This is the case in many parts of Africa, where drug resistance is thought to be on the rise.
What causes MDR-TB?
MDR-TB is caused by poorly managed treatment of TB disease: when patients do not take all their medicines regularly for the required period because they start to feel better, when health workers prescribe the wrong drugs or the wrong combination of drugs, or when the drug supply is unreliable or of poor quality.
When patients fail to complete treatment regimens or receive incorrect treatment, they may remain infectious. Bacteria in their lungs may develop resistance to certain anti-TB drugs, which then can no longer kill the bacteria. People they infect will acquire the same drug-resistant strain. When drug treatment stops, the bacteria build up resistance to medication, reducing options for further treatment.
The end result is MDR-TB, a form of TB that doesn't respond to treatment.
Who is at risk for MDR-TB?
Drug resistance is more common in people who:
Have spent time with someone with drug-resistant TB disease
Do not take their prescribed medicine regularly
Do not take all their medicine
Develop TB disease again, after having taken TB medicine previously
Come from areas where drug-resistant TB is common (South East Asia, Latin America, Haiti and the Philippines)
Can MDR-TB be treated?
Patients with MDR-TB disease must be treated with special drugs, which are not as good as the usual anti-TB drugs and may cause more side effects. Even these drugs have little effect on XDR-TB.
Some people with MDR-TB disease must consult a TB specialist to observe their treatment to check its effectiveness. MDR-TB is at least 100 times more expensive to cure than non-resistant TB. At best, only half those infected with new strains can be cured. There is no cure affordable to developing countries for some MDR strains.
The worst scenario is that TB will become untreatable due to MDR-TB. MDR-TB usually kills its host, but only after allowing the victim years of life to spread drug-resistant bacteria to others.
Can MDR-TB be prevented?
People who have spent time with someone with MDR-TB disease can become infected with MDR-TB bacteria. If they have a positive skin test reaction, preventive therapy is important for those at high risk of developing MDR-TB disease, such as children and HIV-infected people.
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