What are the probable causes of Drug Resistant TB?

• The disease has already progressed too far, as often occurs with cancer.
• Stronger strains of TB have emerged.
• In Third World countries many infected people are treated for TB but not treated for malnutrition.
• In Third World countries people are constantly being re-infected through ingestion of contaminated food and drink and constant contact with infected people, animals and soil.

Ref: Infectious disease: TB's revenge