About one quarter of previously untreated TB patients were infected with the multi-drug-resistant TB.

WSJ: Tuberculosis Strain in Mumbai Doesn't Respond to Main Treatment

They then develop resistance to several medications, thus infecting their communities with multi-drug resistant strains of TB.

CNN: The Killer Cough

Partially drug-resistant TB can now found in countries across the world, and "multi-drug resistant" strains affect countries such as Russia and China.

BBC: Indian TB cases 'can't be cured'

In Uttar Pradesh, India's most populous state with 200 million people, a study published in 2008 in the Indian Journal of Medical Research showed about 20% of TB patients were multi-drug-resistant.

WSJ: Tuberculosis Strain in Mumbai Doesn't Respond to Main Treatment

When China released its first nationwide survey this year, it found 5.7% of that country's newly diagnosed TB patients were multi-drug-resistant, according to a study published this year in the New England Journal of Medicine.

WSJ: Tuberculosis Strain in Mumbai Doesn't Respond to Main Treatment

The WHO's latest estimate that about 2.1% of previously untreated and 15% of previously treated TB patients in India are multi-drug-resistant is based on surveys done by just a few Indian states, he said.

WSJ: Tuberculosis Strain in Mumbai Doesn't Respond to Main Treatment