Half a million people fell sick with dangerous superbug strains of tuberculosis in 2012, but fewer than one in four were diagnosed, putting the rest at risk of dying from wrong medicines or no treatment at all.
The latest data from the World Health Organization, which says drug-resistant TB is a "global health security risk," showed a third of the estimated 9 million people who contract TB in any form each year do not get proper care.
This has led to drug resistance spreading around the world at an alarming rate and has given rise to incurable strains of the bacterial infection - known as totally drug-resistant TB - which cannot be treated with any known medicines.
"Earlier and faster diagnosis of all forms of TB is vital," said WHO director general Margaret Chan. "It improves the chances of people getting the right treatment and being cured, and it helps stop spread of drug-resistant disease."
Last year the WHO called for multidrug-resistant tuberculosis to be recognized as a public health crisis. It said the contagious, deadly superbug forms of the disease carry "grave consequences for those affected."
Treating even regular TB is a long process. Patients need to take a cocktail of antibiotics for six months and many fail to complete the treatment.