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tries and cause increased crowding in urban areas, thereby facilitating tuberculosis transmission. Increasing economic gradients increase the allure of wealthier countries for poor people in the developing world. In many parts of the world, wars, worsening economic circumstances, reordering of priorities, and lack of political commitment have all led to deterioration in the public health infrastructure while, at the same time, the need for disease control programs and surveillance is increasing. Consequently, overall, there are probably more cases of tuberculosis in the world today than there have ever been. It would be easy to blame human immunodeficiency virus (HIV) infection for the world's worsening tuberculosis situation, and, clearly, it is an important factor. However, one could contend that HIV merely illuminated the existing weaknesses of existing tuberculosis control programs.

In view of the current state of global tuberculosis control efforts, it is not surprising that in low-incidence countries, increasing proportions of new cases are arising from among individuals born in high-incidence areas. In general, low-incidence, industrialized countries have in place screening processes by which applicants for immigrant visas are examined for tuberculosis and individuals with infectious tuberculosis are denied visas. However, the systems are imperfect and, depending on the circumstances, may break down entirely. For example, because of the need for rapid resettlement of a large number of Southeast Asian refugees in the United States in the late 1970s, screening for tuberculosis was not performed. As a consequence, persons with active tuberculosis entered the country, resulting in a reduction of the previous years' rate of decline and an actual slight increase in the number of cases of tuberculosis in 1980. San Francisco was the destination for many of the refugees, and the number of cases rose from approximately 300 in 1978 to 400 in 1979 to 500 in 1980. A similar impact on case numbers was seen in Hawaii with the unannounced arrival of a large number of Filipino World War II veterans who much earlier had been promised citizenship in return for serving in the U.S. armed forces.

The combination of the natural history of tuberculosis, with its often long period of latency and the high prevalence of both latent infection and disease in many parts of the world, together with the many factors that cause individuals and groups of people to move from country to country ideally suits global distribution of the disease. The phenomenon of the globalization of tuberculosis is clearly seen in most industrialized countries. In the United States foreign-born persons made up 41 percent of the new cases reported in 1998 (see Chapter 2). During the 1990s, this proportion has progressively increased, in part because the intensified control measures applied early in the 1990s were directed more toward U.S.-born individuals. As noted in Chapter 2 , the proportion of cases among U.S.-



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