The principle of preventing the spread of infectious disease by which people, baggage, merchandise, etc, likely to be infected or coming from an infected place are isolated at frontiers or ports until their harmlessness has been proven to the satisfaction of the authorities. (See INFECTION.)

Originally it involved detention for 40 days; but the period now covers the INCUBATION period of the disease whose presence is suspected.

Numerous international conferences upon the subject have been held with the view of arriving at a uniform practice as regards quarantine in different countries. Amongst diseases to which quarantine still applies are CHOLERA, YELLOW FEVER, PLAGUE, SMALLPOX, TYPHUS FEVER and RELAPSING FEVER.