but also fire control, housing, and others—has been inferred by Wallace (43), who decried how planned reduction in capacity to contain urban fires led to spreading urban decay, and the physical and social "ghettoization" of the Bronx. While sexual behaviors and health care most directly determine the rate of introduction and removal of bacterial STDs in the population, the patterns of introduction, spread, and removal within and between communities are determined by social networks and spatial factors, influenced by urban/community planning and services.

Quinn (46) discusses these factors separately in this volume as determinants of the spread of HIV infection. They equally influence spread of bacterial STD. The possible contribution of epidemic urban decay and resulting migration described by Wallace (43) to the reemergence of gonorrhea, syphilis, and chancroid in the United States provides one example. Global examples include the epidemic increases in gonorrhea and syphilis in the industrialized countries during and after World Wars I and II and in the United States during and after the Vietnam War, and the rapid global spread of two types of β-lactamase-encoding plasmids in gonococci from separate regional foci in Asia and Africa in the 1970s. The resurgence of reported STDs in China (Figure 1) accompanied reopening of the country to foreign visitors, movement of the male work force within the country to industrial centers, and reemergence of a commercial sex industry in response. Similarly, the growth of the commercial sex industry in Thailand accompanied increased military, work-related, and tourist travel and urbanization, all of which fueled epidemic STD (Figure 2). Indeed the classic tendency of one country to attribute STD epidemics to another country (e.g., syphilis, as both "The French Disease" in Italy and "The Italian Disease" in France at the end of the 15th century) generally reflects changing behaviors in both countries during periods of war, migration, or increased travel.

Figure 3 contrasts the age distribution of the population of the world's developing regions with that of the industrialized countries in 1980 and shows projected growth to the year 2000. Young people predominate now in developing regions and will become even more predominant. Furthermore, the percentage of the world's population living in urban areas will grow from 37% in 1985 to 45% by the year 2000 and to 61% by