of MDR TB patients. It is estimated that 50 percent of MDR TB cases worldwide occur in China and India. Other countries with large numbers of MDR TB cases include Bangladesh, Indonesia, Myanmar, Nigeria, Pakistan, the Philippines, and South Africa.
This chapter begins by briefly reviewing the difficulties involved in estimating the burden of MDR TB. It then looks at MDR and XDR TB first in South Africa and then in China. The fourth section presents an historical perspective on MDR TB control efforts. The final section details remaining challenges in global efforts to combat MDR TB.
The official figures for MDR TB prevalence and incidence raise many questions. Farmer cited official numbers of 1.5 million cases of MDR TB, with 500,000 new cases annually. But he raised the question of how prevalence could remain at 1.5 million with 500,000 new cases annually given existing rates of mortality and transmission.
Farmer acknowledged that estimating the prevalence and incidence of diseases such as TB is extremely complicated. In Lesotho and Peru, for example, similar conditions exist. They include poor health care infrastructures, limited access to diagnostics, fragmented health care delivery systems, a lack of public support for TB care, varying levels of knowledge about TB among providers, inadequate infection control, and a shortage of appropriate drugs for circulating strains. However, the importance of these factors differs considerably between the two countries. In Lesotho, for example, transnational migration is a significant part of the problem, but it is much less important in Peru. These differences make modeling and quantification difficult. Farmer quoted the French poet Paul Valéry: “All that is simple is false, and all that is complex is useless.”
Farmer noted that modeling is a good way to estimate the size of a problem. It may be the case, as some have insisted, that half of TB cases are not diagnosed at all and that the number of drug-resistant TB cases is unknown. But important progress has been made in the past decade. XDR TB is recognized as a serious health issue. Molecular diagnostics have created a much deeper understanding of the resistance problem. According to Farmer, it will be especially useful to link a social medicine perspective on the disease with new molecular techniques to better appreciate the dimensions of the epidemic, as well as the directions in which it is headed (see Box 2-1).
1 This section is based on the presentation of Dr. Farmer.