"Isolation and quarantine are public health practices used to stop or limit the spread of disease. Isolation is used to separate ill persons who have a communicable disease from those who are healthy. Isolation restricts the movement of ill persons to help stop the spread of certain diseases. For example, hospitals use isolation for patients with infectious tuberculosis. Quarantine is used to separate and restrict the movement of well persons who may have been exposed to a communicable disease to see if they become ill. These people may have been exposed to a disease and do not know it, or they may have the disease but do not show symptoms. Quarantine can also help limit the spread of communicable disease. Isolation and quarantine are used to protect the public by preventing exposure to infected persons or to persons who may be infected. In addition to serving as medical functions, isolation and quarantine also are 'police power' functions, derived from the right of the state to take action affecting individuals for the benefit of society."
Division of Global Migration and Quarantine: http://www.cdc.gov/ncpdcid/dgmq/