THE GRAVITAS OF Yersinia pestis, unique among pathogens, is based more on its history than on modern case numbers. When new outbreaks of plague are reported in the media, journalists are quick to link these incidents with the horrors of the medieval Black Death—and then to claim that there is no real threat to society, because we now have modern antibiotics. Walking a thin line between stirring up interest and not causing panic, reporters are only half right on both counts. On the one hand, modern plague cases are caused by the same lethal bacterium, Yersinia pestis; and yet the phenomenon of the Black Death was far greater than any of the isolated cases or small outbreaks that usually attract such attention today. On the other, antibiotics are not a panacea that can wholly protect us from the next pandemic. Plague is re-emerging in a world of growing antibiotic resistance, economic interdependence, and rapid transit. Yersinia pestis is found in enzootic foci on every inhabited continent except Australia, and it was found in the arsenals of some states in the twentieth century. Political instability and weak economies can prevent the growth of adequate public health infrastructures that would enable rapid response to large infectious disease outbreaks, natural or not. Air travel makes pneumonic plague quickly transferable from one site to another. If public health officials and environmental services do their due diligence, an isolated case in the United States (or in most other countries) should not be cause for panic. However, the outbreak of over a hun-dred pneumonic plague cases, something that occurred in Congo in 2004 and 2005, was almost ignored by the media even though this was a serious risk to regional health. Sensationalizing the plague does not help us to deal with these realities, but neither does the lack of attention given to plague in areas of the world that are often beneath our notice.

This essay addresses three basic questions. First, what does it mean for plague to be classified as a re-emerging infectious disease? Second, what is the human incidence of plague around the world today?