The roots of epidemiology can be traced to Hippocrates, a Greek physician
who lived from about 460 to 375 BCE and who is sometimes referred to as
the first epidemiologist. Hippocrates and other members of the Hippocratic
School believes that disease not only affects individuals but also affects the
masses. This was one of the earliest associations of the occurrence of
disease with lifestyle and environmental factors, specifically geographic
location (Lawson & Williams, 2001). Not until the late 19th century however,
did modern epidemiology come into existence.
An epidemic refers to a disease occurrence that clearly exceeds the
normal or expected frequency in a community or region. In past
centuries, epidemics of cholera, bubonic plague, and smallpox swept
through community after community, killing thousands of people,
changing the community structure, and altering the lifestyle of masses
of people.
Epidemiology -M. SC. Alaa aldaami
‫المحاضره‬
‫الثانيه‬

When an epidemic, such as the bubonic plague (also called pneumonic plague or
the Black Death) or acquired immunodeficiency syndrome (AIDS), is worldwide
in distribution, it is called a pandemic.
Epidemic and pandemic diseases clearly prompted the development of
epidemiology as a science. Epidemiology became a distinct branch of medical
science through its concern with massive waves of infectious diseases. In 1348
and 1349, the Black Death (likely caused by the bacillus Yersinia pestis) swept
through continental Europe and England, killing millions of people. In England
alone, the epidemic resulted in the deaths of 30% to 60% of the population
(Theilmann & Cate, 2007).