Strains of TB that are resistant to a single drug have been documented in every country surveyed and strains that are resistant to all the major drugs have emerged. The treatment of multi-drug resistant TB is complex, time consuming and difficult for both patient and doctor. It requires up to two years of treatment with drugs that can be 100 times more expensive than the standard treatment. For many countries already struggling to implement an effective TB programme this extra cost can be prohibitively expensive. Patients may not take all their drugs because of side effects, or not complete the whole course because they start to feel better.
Medical ignorance can also be a problem, with doctors prescribing the wrong treatment regimens.
In many countries the supply of drugs is not reliable. According to the WHO, poorly supervised or incomplete treatment of TB is worse than no treatment at all. Such patients remain infectious and the bacilli in their lungs may develop resistance to anti-TB drugs. People they infect will have the same drug-resistant strain. Other countries with a high prevalence or drug resistance include China, Iran and Russia.