A cordon sanitaire (, French for "sanitary cordon") is the restriction of movement of people into or out of a defined geographic area, such as a community, region, or country. The term originally denoted a barrier used to stop the spread of infectious diseases. The term is also often used metaphorically, in English, to refer to attempts to prevent the spread of an ideology deemed unwanted or dangerous, such as the containment policy adopted by George F. Kennan against the Soviet Union (see cordon sanitaire (politics)). Origin The term cordon sanitaire dates to 1821, when the Duke de Richelieu deployed French troops to the border between France and Spain, to prevent yellow fever from spreading into France. Definition A cordon sanitaire is generally created around an area experiencing an epidemic or an outbreak of infectious disease, or along the border between two nations. Once the cordon is established, people from the affected area are no longer allowed to leave or enter it. In the most extreme form, the cordon is not lifted until the infection is extinguished. Traditionally, the line around a cordon sanitaire was quite physical; a fence or wall was built, armed troops patrolled, and inside, inhabitants were left to battle the affliction without help. In some cases, a "reverse cordon sanitaire" (also known as protective sequestration) may be imposed on healthy communities that are attempting to keep an infection from being introduced. Public health specialists have included cordon sanitaire along with quarantine and medical isolation as "nonpharmaceutical interventions" designed to prevent the transmission of microbial pathogens through social distancing. The cordon sanitaire is not used now in its most extreme historical form. This is partly due to our improved understanding of disease transmission, treatment and prevention. In modern days, its function is more to allow easier identification and control over contagion spreading. For example, in China, in tightly controlled cordons one delegated family member might have been given an exit pass to do daily shopping, while in loosely controlled cordons individuals might be permitted to enter and exit without control (other than a temperature check) through a main entrance, while other entrances are temporarily blocked. In its more traditional role, the cordon also remains a useful intervention under conditions in which: 1) the infection is highly virulent (contagious and likely to cause illness); 2) the case fatality rate is very high; 3) treatment is nonexistent or difficult;