ago in one of the Mesopotamian river valleys (Preston, 1999). In addition, population migrations and new areas of human habitat during the past century have led to the emergence and reemergence of pathogens unaffected by current medical treatments (IOM, 1992). The phenomenon of antibiotic resistance is alarming because antibiotic-resistant pathogens are cumulative and accelerating (IOM, 1998a; Feikin et al., 2000). The loss of treatment alternatives makes the prevention of communicable disease through immunization ever more critical.

In addition to pathogen evolution, increased global travel has changed disease patterns throughout the world. In 1998, more than 53 million individuals flew on U.S. carriers to domestic and international locations. Travelers, businesspeople, immigrants, and migrants make national and state boundaries ineffectual barriers to disease in the United States. The IOM report Emerging Infections: Microbial Threats to Health in the United States summarizes the threat posed by the increased global movements of people:

As the human immunodeficiency virus (HIV) disease pandemic surely should have taught us, in the context of infectious disease, there is no-where in the world from which we are remote and no one from whom we are disconnected. Consequently, some infectious diseases that now affect people in other parts of the world represent potential threats to the United States because of global interdependence, modern transportation, trade, and changing social and cultural patterns (IOM, 1992:v).

The September 1999 outbreak of a West Nile-like virus in New York serves as a reminder of how easily disease can spread across the global community. This was the first time the West Nile-like virus, contracted from mosquitoes that have bitten infected birds, had ever been reported in the Western Hemisphere (CDC, 1999d).

Population Demographics

The worldwide movement of people, especially through immigration and migration, continually changes U.S. population demographics, affecting susceptibility to infectious diseases and placing increased demands on the national immunization effort. For example, immigrants accounted for 35 percent (7,930) of total U.S. tuberculosis cases in 1995 (IOM, 1998b). One of every five children under age 18 in the United States (14 million) is an immigrant or has immigrant parents (IOM, 1998b). Since foreign birth has been identified as a barrier to immunization, immigrant children and adults are likely to fall further behind in vaccination coverage unless special efforts are made to integrate them into the U.S. health care system (Findley et al., 1999).

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