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It is estimated that 1 to 1.5 million people worldwide are living with multidrug-resistant tuberculosis. In 2006, one in every 20 of all new cases of tuberculosis was multidrug-resistant. Of the nearly half a million people who became ill with multidrug-resistant tuberculosis, 50% were in China and India, and 7% in the Russian Federation.
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The lowest levels of drug-resistance are in Western and Central Europe, followed by Africa and the Americas. The Eastern Mediterranean and South East Asia are moderately affected, followed by the Western Pacific. Eastern Europe reports the highest proportions of drug-resistance.
There are important variations within the WHO regions, particularly in the Eastern Mediterranean, the Western Pacific, and the European regions. For example, there is much less drug-resistant TB in Western and Central Europe than in Eastern Europe. In all regions, there are some countries where the results are very different from the average.
Data on the evolution of the occurrence of tuberculosis and drug-resistance show different trends. For example, the proportion of multidrug-resistant tuberculosis (MDR-TB) among new TB cases is decreasing rapidly in Hong Kong, China and the United States while it appears to be stable in Thailand, Viet Nam, in three Baltic countries and in many countries with a low TB burden.
In South Korea and in Peru, TB cases are declining, although at a slower pace than before, and the number of cases of multidrug resistant tuberculosis is increasing. In Peru this is probably caused by weaknesses in tuberculosis control. In South Korea, the results could be due to a better surveillance system that is now detecting cases that would not have been detected in the past.
In some parts of the Russian Federation, the overall number of new TB cases is not as high as in previous years but the proportion of new cases that are multidrug-resistant is increasing very rapidly.
At present it is not possible to estimate global trends because there is very little information on trends from high burden countries.
Data on trends can be misleading. For instance, an improvement in testing would detect previously unreported cases and therefore lead to an apparent increase in multidrug-resistant tuberculosis. An increase in the reported proportion of drug resistance in a population could also be due to a better control programme that cures more TB cases overall, but cannot cure resistant forms of the disease. Therefore, when evaluating the trends, it is important to interpret the data carefully, to consider additional information and to take into account any changes in TB control programmes that could affect the data.
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Extensively drug-resistant tuberculosis (XDR-TB) is more expensive and difficult to treat than multidrug resistant tuberculosis (MDR-TB) and outcomes for patients are much worse because the treatment options are limited. Therefore, it is important to know how many cases of XDR-TB there are and how they are distributed.
The available data on XDR-TB have several limitations. Firstly, the quality of the tests for resistance to second-line drugs is not sufficiently ensured as most tests were not carried out by supranational reference laboratories. Secondly, second-line drug susceptibility testing is not available in most countries because of its significant cost. Therefore, in most settings only MDR-TB cases were tested for resistance to second-line drugs, which may limit the accuracy of the estimates of the levels of XDR-TB.
Despite these shortcomings, data indicate that XDR-TB is widespread with 45 countries having reported at least one case. However, no conclusions can be drawn about the total number of cases worldwide because most of the information available is from countries that report few TB cases.
Japan and South Korea have reported high rates of XDR-TB but these may be overestimates because the test population was not representative. The Philippines might also be heavily affected. In Africa the problem of XDR-TB may be less, except in South-Africa. In the countries of the former Soviet Union, where drug resistance is widespread a very high proportion of cases of MDR-TB are XDR-TB.
Data from many parts of the world is still sparse, highlighting the need for a strengthening of the global capacity for diagnosis and surveillance of resistance to second-line drugs.
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