Question

What is an epidemic disease?
A. A global outbreak of disease.
B. A disease that occurs suddenly and spreads rapidly to many people.
C. A disease that occurs only occasionally and at unpredictable intervals.
D. A disease with clinically distinct symptoms whose incidence has increased, particularly over the last two decades.

Answer 1

Hint: The term epidemic comes from a word form attributed to Homer's Odyssey, which later took on medical significance thanks to Hippocrates' treatise Epidemics. Epidemios, epidemeo, epidamos, and other variants had meanings that were similar to the current definitions of "indigenous" and "endemic" before Hippocrates. One of the earliest accounts of the Plague of Athens is Thucydides' description.

Complete answer:
An epidemic occurs when a disease spreads rapidly to a large number of people in a population in a short period. In meningococcal infections, for example, an attack rate of more than 15 cases per 100,000 people for two weeks is considered an epidemic.
A change in the ecology of the host population (e.g., increased stress or increased density of a vector species), a genetic change in the pathogen reservoir, or the introduction of an emerging pathogen to a host population are all common causes of infectious disease epidemics (by the movement of pathogen or host).
In most cases, an epidemic occurs when host immunity to an established pathogen or a newly emerging novel pathogen is suddenly reduced below that found in the endemic equilibrium, and the transmission threshold is crossed.
An epidemic can be localized; however, if it spreads to other countries or continents and affects a large number of people, it is referred to as a pandemic. A good understanding of a baseline rate of incidence is usually required to declare an epidemic; epidemics for certain diseases, such as influenza, are defined as reaching some defined increase in incidence above this rate.

Thus, the answer is option B: A disease that occurs suddenly and spreads rapidly to many people

Note:
A few cases of very rare disease might be classified as an epidemic, but many cases of a common disease (like the common cold) wouldn't. In addition to impaired health and loss of life, an epidemic can cause enormous financial and economic losses.