Epidemic , Endemic, Pandemic

Endemic is defined as the usual occurrence of a disease within a population. In contrast, an epidemic is a sudden and great increase in the occurrence of a disease within a population. It may also be the first occurrence of an entirely new disease. An epidemic can give rise to a pandemic, which is a rapidly emerging outbreak of a disease that affects populations across a wide geographical area. Pandemics often are worldwide in scope. As an illustration of the three types: small numbers of people may be affected by influenza throughout the year in a large city; those individuals would be considered endemic cases of the disease. If the number of people affected by influenza in the same city increases to high levels in the winter, the outbreak would be considered an epidemic. If a new variety of influenza emerges and affects people throughout the world, the outbreak would be considered a pandemic. An example of a pandemic is the influenza pandemic of 1918–19, which spread to countries worldwide and killed an estimated 20 million–50 million people.