A pandemic example, depicting the number of new infections over time.
The rapid spread of disease to large numbers of people in a specific population in a short period of time is referred to as an epidemic. An epidemic of meningococcal infections, for example, is defined as a rate of more than 15 cases per 100,000 persons for two weeks.
Infectious illness outbreaks are frequently caused by a change in the host population’s environment (for example, increased pressure or a high density of vector species), a genetic mutation in the pathogen reservoir, or the advent of new diseases.
In a population of hosts (by pathogen or host movement).
When the host’s immunity to a confirmed or developing disease falls below endemic equilibrium and the transmission threshold is exceeded, an epidemic ensues.
The outbreak may be contained in a single location. It is referred to as a pandemic when it spreads to other nations or continents and affects a huge number of people.