Quarantine

Quarantine is a public health measure that keeps people who have been exposed to an infectious disease, but who are not ill, apart from others for a set time. It serves two purposes: to watch whether they develop the disease, and to stop them spreading it if they turn out to be infected, since some people can pass on an infection before symptoms appear. Its length is usually chosen to cover the incubation period, the time between infection and the first symptoms.

Quarantine is not the same as isolation. Isolation separates people who are already sick or confirmed to be infected, while quarantine applies to those who are well but may be incubating the disease. Both can be voluntary or ordered by law, and both are often paired with contact tracing, which finds the people a patient has been near. Animals, plants and goods can also be quarantined, for example at borders to keep out rabies or crop pests.

Quarantine as a formal rule began during 14th-century plague outbreaks, when Adriatic ports such as Ragusa (now Dubrovnik) and Venice made ships from infected places wait offshore before anyone could land. The wait was eventually set at 40 days, and the word comes from the Italian quaranta giorni, meaning forty days.