Governments act through laws passed by legislatures. These laws are of two types: criminal laws, which are intended to punish wrongdoing, and civil laws, which are intended to direct future behavior. Criminal laws are enforced by local prosecutors, state attorneys general, and the Justice Department. Civil laws are enforced by administrative agencies and through litigation by private parties. These range in size and complexity from the Internal Revenue Service and the Department of Health and Human Services, which have bigger budgets than some states, to small, specialized agencies with no full- time staff. Public health departments are among the oldest of administrative agencies, with some dating from the colonial period.

Criminal laws and regulations must be passed by the legislature, they must be specific, and they cannot be modified by the law enforcement agency based on its expertise. Persons accused of committing a crime have the right to remain silent, confront their accusers, and present witnesses, as well as the right to have   counsel, a trial by jury, and certain other protections attendant on their criminal prosecution. These rights make criminal prosecutions slow and expensive, and they also limit the ability of law enforcement to respond to new problems.

The advantages of administrative agencies are so great that legislatures sometimes pass laws that impose punishments, while claiming they are administrative laws, to avoid giving individuals full criminal law protections. While the courts generally accept the legislature's determination that a law is not a criminal law, they do examine the law and its effects as it is applied.

A law that required the permanent quarantine of persons accused of murder to protect the public's health, for example, would be a criminal law because it is based on past behavior rather than on proof of present danger to the community. Accused murderers are therefore entitled to full criminal law protections before being locked away. In contrast, if it can be that persons who commit a violent sexual assault have a high probability of committing future assaults, then it would be acceptable to lock up these persons as a threat to the public health without full criminal law protections. This is an administrative action, even though the person is locked up in a prison.[Allen v Illinois, 478 US 364 (1986).] It is the purpose of the law that matters, not the conditions of confinement.

Public health restrictions were once carried out in prisons and jails. In one case, disease carriers were quarantined in a prison. They petitioned the court for release, claiming that they were being punished by being put in prison and treated as prisoners. The court rejected their claim and concluded the following:

While it is true that physical facilities constituting part of the penitentiary equipment are utilized, interned persons are in no sense confined in the penitentiary, and are not subject to the peculiar obloquy which attends such confinement.[Ex Parte McGee, 185 P 14,16 (Kan 1919)]

Most public health law cases were decided decades ago, and the U.S. Supreme Court gave individuals few rights. Some argue that these cases were superseded by the Supreme Court's civil liberties decisions in the 1960s and 1970s. In these rulings, the Supreme Court required criminal law protections in several cases where the legislature had said that the law was not intended to punish. In other cases, the Court recognized a right of privacy that might also apply to public health laws.

While the current Supreme Court has not directly affirmed traditional public health cases, it has upheld public health rationales in other contexts.[Richards EP, Rathbun KC. Law and the Physician, A Practical Guide. Boston, Mass: Little Brown & Co; 1993] For example, it specifically rejected the Warren Court's consideration of the conditions of confinement in determining whether public safety detention is punishment. The Court rejected arguments that detainees should be held in the least restrictive manner necessary to ensure their confinement. Instead, the Court allowed them to be kept with other prisoners and subjected to the same prison rules. Despite the detainees' apparent imprisonment, the Court ruled that their incarceration was not a punishment because the state's intent  was merely to protect the public until the detainees could be tried.

Pretrial detention cases may prove more than is  necessary to uphold public health restrictions. The  difficult problem in the detention of criminally dangerous persons is determining the probability that they will endanger public safety by committing another crime. This probability is certainly less than 100 percent, perhaps substantially less. In contrast, communicable diseases can be objectively diagnosed and their risk assessed. Persons with diseases such as active tuberculosis are dangerous, irrespective of  whether they intend to harm others.