Dr. Howard Markel, the author of When Germs Travel, talked about the history and present state of a variety of contagious diseases. In his book, he chronicles six epidemics or outbreaks that occurred in America over the last century: trachoma, bubonic plague, tuberculosis, AIDS, cholera, and typhus fever.

Markel outlined how these epidemics share a set of common features, which include panic (often fueled by media reports), quarantines and/or the closing down of ports, and the scapegoating of a certain group (such as immigrants) who are blamed for bringing in the disease.

Along with AIDS, tuberculosis remains one of the top health threats, he said, noting a 1996 case in which a TB-infected woman traveled on a long plane flight from Seoul to Baltimore, and 29 people sitting near her came down with the illness. Influenza is another worry, and the medical community keeps a constant vigil for deadly strains of the virus, such as the one that wiped out millions in 1918, he noted.