"Recent quarantine policies announced by several states, including New York and New Jersey, for travelers arriving from areas affected by the outbreak of Ebola Virus Disease have raised legal and constitutional questions about federal and state authority to order quarantine and isolation measures. Both the federal and state governments have authority to impose isolation and quarantine measures to help prevent the spread of infectious diseases. While the terms are often used interchangeably, quarantine and isolation are two distinct concepts. Quarantine typically refers to separating or restricting the movement of individuals who have been exposed to a contagious disease but are not yet sick. Isolation refers to separating infected individuals from those who are not sick. Historically, the primary authority for quarantine and isolation exists at the state level as an exercise of the state's police power in accordance with its particular laws and policies. Generally, state and local quarantines are authorized through public health orders, though some states may require a court order before an individual is detained. The Supreme Court has indicated that at least where Congress has not taken action, it is 'well settled' that states may impose quarantines to prevent the spread of disease. Nevertheless, the federal government has jurisdiction over interstate and foreign quarantines. The Centers for Disease Control and Prevention (CDC) is authorized to take measures 'to prevent the introduction, transmission, or spread of communicable diseases from foreign countries into the States or possessions, or from one State or possession into any other State or possession.'"
CRS Legal Sidebar, October 28, 2014