Incidences of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) -- associated with high mortality rate -- is on the rise in India, while threatening to derail the progress achieved in controlling the disease, researchers say.

Nearly one in five cases of TB are now resistant to at least one major anti-TB drug and approximately five per cent of all cases of TB are classed as MDR (resistant to two essential first-line TB drugs, isoniazid and rifampicin) or XDR (also resistant to fluoroquinolones and second-line injectable drugs). 

MDR and XDR-TB which are associated with high mortality -- 40 per cent for MDR-TB patients and 60 per cent for XDR-TB patients -- are a threat to health-care workers, prohibitively expensive to treat and are therefore a serious public health problem, the researchers noted. 

"TB exists on an epic scale in India, and cases of multidrug resistant TB are an increasing concern. Access to drugs to treat TB, including drug resistant TB is a major concern," said Zarir Udwadia from Hinduja Hospital & Research Centre in Mumbai. 

TB, caused by a bacterial species called Mycobacterium tuberculosis, is estimated to have killed 1.8 million people worldwide in 2015. Out of these, six countries -- India, Indonesia, China, Nigeria, Pakistan and South Africa -- accounted for 60 per cent of the total number of cases of TB. 

Globally in 2015, there were an estimated 480000 cases of MDR-TB, with approximately half of these cases being in India, China, and Russia, the study, published in the Lancet Respiratory Medicine, said. 

"Resistance to anti-tuberculosis drugs is a global problem that threatens to derail efforts to eradicate the disease. With resistance, the treatment can take years and the drugs used can have unpleasant and sometimes serious side effects," added Keertan Dheda, Professor at University of Cape Town in South Africa. 

Although a small number of repurposed and new drugs have recently become available to treat drug-resistant TB -- including bedaquiline, delamanid, and linezolid --, without accurate diagnostics, clear treatment guidelines and improved control efforts, the effectiveness of the drugs could be rapidly lost, the researchers stated.