This trio of terms describes various degrees of an infectious disease's spread. The process begins with an outbreak—a sudden rise in the presence of a disease. An outbreak that can't be stopped or slowed, and in which the disease is spreading rapidly to many people within a localized community or region (such as a single country), is called an epidemic. The word pandemic refers to an epidemic that has gone international: the disease, once localized in scope, now starts to appear in other countries and even on other continents, typically infecting a large number of people in a short amount of time. A pandemic often has significant economic and social ramifications due to its global impact. If a disease lingers for a long time as an epidemic or a pandemic, it may eventually become endemic to an area. The word endemic describes a disease that persists at a consistent level within a region with fairly predictable rates of infection and spread, making it easier to prevent future outbreaks. Epidemic, pandemic, and endemic all share the Greek root dêmos, meaning "district, country, people."
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