http://sphweb.bumc.bu.edu/otlt/MPH-Modules/PH/PublicHealthHistory/publichealthhistory2.html Quarantine and Isolation The use of quarantine as a public health measure dates back to the 14th century when the Black Death ravaged Italy and the rest of Europe. Quarantine comes from the Italian quarantena, meaning forty-day period. Travelers and merchandise that had potentially been exposed to disease were isolated for a period of time to ensure that they weren't infected. Some cities and towns would create a "cordon sanitaire,' a physical barrier that could only be crossed with permission. This practice persisted into the late 19th century and early 20th century. When plague threatened San Francisco, the Chinese section was quarantined by encircling it with a rope with armed guards to ensure that unauthorized individuals did not pass through. a "cordon sanitaire" was also used during an outbreak of bubonic plague in 1899-1900 in Honolulu's Chinatown. Fourteen blocks of the city were literally cordoned off, isolation 10,000 people.. While quarantine is one of the oldest public health measures, it is still useful today. During the SARS epidemic, Toronto quarantined individuals who had potentially been exposed by confining them to their homes until it was certain that they weren't infected. This measure was effective in controlling SARS because individuals infected with SARS were not infectious until they began to exhibit symptoms. Consequently, if an individual was possibly exposed, but did not yet show symptoms, quarantine prevented them from infecting others. However, quarantine is less useful for diseases like influenza, when an infected person can spread the disease even before they begin having symptoms. Quarantine is different from isolation, which is separation of a person who has the disease; quarantine refers to the separation of an individual who has possibly been exposed to disease.