The word Epidemic is derived from Greek ‘epi’ meaning “upon or above” and ‘demos’ meaning “people”. The word together literally translates to “upon or above people”.
Epidemic is often used to denote infectious diseases that can spread quickly from person to person. In an epidemic, a disease must spread to a large number of people in a short time, most commonly two weeks. The spread of Ebola in West Africa is an example of an epidemic.
Epidemics of diseases are caused by several factors such as a change in the ecology of the host population, a genetic change in the pathogen reservoir or the introduction of an emerging pathogen to a host population.
Epidemic can be limited to a localized region, but can also spread across states and even countries. The spread of a disease across continents and affecting a substantial number of people is known as a pandemic.