What is Drug Resistant TB?

WHO has recently released the 2011 Global Tuberculosis Control Report.

As per this report, the number of people who fell ill with tuberculosis globally dropped to 8.8 million in 2010, after peaking at nine million in 2005.

But for India, the story is sad. It says that in India, the disease still wreaked havoc. It infected over 15 lakh people in 2010 and killed over three lakh.

The report says that India’s case detection rate in 2010 was just about 60%. Globally, it is estimated that 3.3% of all new TB cases had MDR-TB in 2009. Each year, about 4.4 lakh MDR-TB cases are estimated to emerge and 1.5 lakh persons with MDR-TB die. However, according to WHO, 2.1% of all new cases in India are MDR-TB while as many as 15% of retreatment TB cases are developing MDR-TB.

TB is also the most common illness among people living with HIV, including those who are taking antiretroviral treatment. In 2009, 3.8 lakh people died of HIV-associated TB. In India, only 32% of TB patients know their HIV status. Just about two lakh HIV positive people have been screened for TB. At least one-third of the 33.3 million people living with HIV worldwide are infected with TB. Persons co-infected with TB and HIV are 20-30 times more likely to develop active TB disease than persons without HIV.

Drug Resistant TB

Until 50 years ago, there were no medicines to cure TB. Now, strains that are resistant to a single drug have been documented in every country surveyed; what is more, strains of TB resistant to all major anti-TB drugs have emerged. Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their medicines regularly for the required period because they start to feel better, because doctors and health workers prescribe the wrong treatment regimens, or because the drug supply is unreliable. A particularly dangerous form of drug-resistant TB is multidrug-resistant TB (MDR-TB), which is defined as the disease caused by TB bacilli resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs. Rates of MDR-TB are high in some countries, especially in the former Soviet Union, and threaten TB control efforts. (WHO website).

What is MDR-TB ?

TB that is resistant at least to isoniazid and rifampicin the two most powerful first-line anti-TB drugs is called the Multi-drug-resistant tuberculosis (MDR-TB). It develops because the when the course of antibiotics is interrupted and the levels of drug in the body are insufficient to kill 100% of bacteria. This means that even if the patient forgets to take medicine, there are chances of developing MDR-TB.

MDR-TB is treated with secondline of antituberculosis drugs such as a combination of several medicines called SHREZ (Streptomycin+isonicotinyl Hydrazine+Rifampicin+Ethambutol+pyraZinamide)+MXF+cycloserine.

What is XDR-TB?

When the rate of multidrug resistance in a particular area becomes very high, the control of tuberculosis becomes very difficult. This gives rise to a more serious problem of extensively drug-resistant tuberculosis (XDR-TB). XDR-TB is caused by strains of the disease resistant to both first- and second-line antibiotics. This confirms the urgent need to strengthen TB control.

 

Thus, Extensively-drug resistant TB (XDR-TB) is a sub-set of MDR-TB which is further resistant to at least two more drugs which are second line drugs and is thus virtually incurable. XDR TB was first described in March 2006 following a joint survey of laboratories by the WHO, IUATLD, and CDC, Atlanta.

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