A century and a half ago, it took about 365 days to circumnavigate the globe by ship; today it takes less than 36 hours. Thus the incubation period of many infectious diseases is now longer than the time it takes the infected to travel from one location to another. In the past, infectious disease outbreaks were readily detected on ships as they pulled into port, and the ships were quarantined until the diseases had burned themselves out. Now, should a local outbreak spread silently and globally via an infected traveler or tourist, cases will likely start emerging only days or weeks later in clinics and communities worldwide. Human movement has become a process that involves much more than what happens during the trip itself; the impact persists long afterward, particularly with regard to HIV, TB, and other latent infections.
In the meantime, the world’s population has grown exponentially and more people have been on the move than ever before, especially during the past decade. According to Cetron (2002) migration volumes increased fourfold for the period 1960 through the 1990s. In 2001, an estimated 800 million people traveled; were forcibly displaced; or moved to new countries to work, study, join family members, or escape persecution. These individuals included international travelers (698 million), migrant workers (70–80 million), refugees and uprooted people (22 million), undocumented migrants (10–15 million), and migrant victims of human trafficking (0.7 million). This explosion in the rate of human mobility is almost certainly how HIV was introduced into North America and how fluoroquinolone-resistant gonococci were introduced into North America from Asia.
One participant noted that people on the move not only transmit infectious diseases, but also spread antimicrobial-resistant genetic material. A traveler’s immunological system may afford protection from certain strains but not others. Thus, although there is a tendency to think of travelers as targets for infectious disease per se, it was suggested that perhaps they should also be thought of as interactive biological agents that pick up microbes and drug-resistant microbial genetic material in one part of the world and transport them to another. Although the global spread of drug-resistant microbes was not discussed at length during the workshop, with the exception of multidrug-resistant TB (an especially acute problem in Russia), the globalization of antimicrobial-resistant pathogens was identified as a serious, major issue. Another recent Forum workshop, Issues of