Mumbai has recorded a rise in the number of extra extensively drug-resistant TB (XXDR TB). Currently 24 patients have been detected positive for the deadly strain of TB. This figure is 4 times the number of cases that existed at the same time last year. XXDR TB was first found in  2011 in 12 patients admitted to Hinduja Hospital, Mahim. According to the BMC records, of the 12 patients admitted, six died and 18 new cases have been recorded. Since the first reports surfaced about XXDR TB experts have worried about the ramifications of an outbreak in crowded urban centres like Mumbai.

So what exactly is XXDR TB?

Earlier termed totally drug resistant TB (TDR TB) but later renamed XXDR TB, the term refers to an extremely drug resistant TB strain that is impervious to all the first and second line drugs used in tuberculosis treatment. This resilience makes it very hard to treat and contain it.

How TB is caused?

TB is caused by the bacteria Mycobacterium tuberculosis. It is an aerobic (requires high levels of oxygen to survive), non-motile bacterium and transmitted primarily through the air. You can get TB from an infected person when he coughs, sneezes or spits. This bacterium is known to be highly stable and can survive in a dry atmosphere for weeks. A test known as ‘drug sensitivity’ is performed on a TB strain to determine which drug will eradicate the bacterium most effectively.

When the disease first emerged it was treated with a combination of drugs. With time, the bacterium started to develop immunity to the drugs being used. As the bacterium mutated, medical science started to use more potent drugs for its treatment. This cycle resulted in the formation of a strain that is so evolved that it is immune to all medications known to treat the disease.

Why does this happen?

The standard course of treatment for TB lasts between 6 to 9 months. The patient is prescribed isoniazid, rifampicin, pyrazinamide, and ethambutol for two months, followed by isoniazid and rifampicin for a further four months. In the case of latent tuberculosis the treatment lasts for 6-9 months of isoniazid alone. A patient is considered cured after six months, when sputum analysis is done to check for presence of the bacilli. This is done because a person can be a carrier of the bacilli without showing any symptoms which makes the person capable of passing on the infection without suffering from the disease.

Why discontinuing treatment is dangerous

It has been seen that patients tend to discontinue treatment once they start feeling better. This is usually around the 4th month of treatment. Discontinuation of medication, results in the particular strain of Mycobacterium developing resistance to the medication that the person was prescribed, leading to multi drug resistant TB. On discontinuing treatment the person is infected yet again, but this time with a more potent and drug resistant form of the bacterium. XXDR TB is the result of people mutated bacteria that have been passed on from previously ill patients and latent carriers of the disease.

Also read: How you can prevent tuberculosis