Hippocrates in ancient Greece is considered one of the first epidemiologists for associating disease occurrence with lifestyle and environmental factors like geographic location. An epidemic refers to a disease exceeding normal frequency in a community, with epidemics in the past of cholera, plague, and smallpox killing thousands and altering societies. A pandemic is an epidemic occurring worldwide, and massive waves of infectious disease clearly drove the development of epidemiology as a scientific field concerned with such outbreaks.