Quarantine is the isolation of a person or animal afflicted with a communicable disease or the prevention of such a person or animal from coming into a particular area, the purpose being to prevent the spread of disease. The power of governments to quarantine is an essential aspect of maintaining the public health, and dates back to 1377, when Venice required Crusader ships to wait forty days in port after returning from Arabia.

In modern American law, the authority to quarantine is a basic power of a health authority and a proper exercise of the police power. Federal law even acknowledges the power to quarantine and provides for the cooperation between federal and state or local health authorities in implementing quarantine laws. 42 U.S.C. § 243(a).

The quarantine exception to liability applies to the liability of public health officers under the tort claims acts. The FTCA states that the federal government will not be held liable for “[a]ny claim for damages caused by the imposition or establishment of a quarantine by the United States.” 28 U.S.C.§ 2680(f). Federal liability is precluded even if the quarantine is shown to have been unnecessary and costly. For instance, a federal court held that the government's withholding of test samples and negligent informing of plaintiff that diseased livestock was free of hoof and mouth disease was covered by the quarantine exemption. Saxton v. United States, 456 F.2d 1105, 1106 (8th Cir. 1972).

In another case, a USDA doctor imposed quarantine on hogs, and injected them with hog cholera vaccine after erroneously diagnosing them with hog cholera. Many died as a result of the hazardous vaccine. The federal appeals court held that the FTCA quarantine exemption barred any claim against the government or the doctor. The court also stated that any negligence in procedures, either through diagnosis or testing, by which the government doctor arrived at the decision to impose quarantine, would also be barred. Rey v. U.S ., 484 F.2d 45 (5th Cir. 1973).