An epidemic is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.
The Plague of Athens (c. 1652–1654) by Michiel Sweerts, illustrating the devastating epidemic that struck Athens in 430 BC, as described by the historian Thucydides
Anopheles mosquito, the vector of malaria
Possibilities for zoonotic disease transmissions
Neisseria meningitidis, often referred to as the meningococcus, is a Gram-negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. The bacterium is referred to as a coccus because it is round, and more specifically a diplococcus because of its tendency to form pairs.
The growth of Neisseria meningitidis colonies on New York City agar
Neisseria meningitidis in cerebrospinal fluid (CSF) seen by Gram stain at 1000× magnification