As a public health measure, quarantine has come to mean the restriction of disease carriers to an environment where their contact with outsiders is limited. Quarantine was widely used until the 1950s. For self-limited diseases such as measles, the infected person was required to stay home and not have visitors. For diseases such as infectious tuberculosis before antitubercular agents were available, the quarantine might be at a sanitarium with other tuberculosis patients.

Isolation, a special case of quarantine, is almost always used in an institutional setting. It may be reverse isolation, to protect the person being isolated. The most famous reverse isolation case was the “bubble baby,” the child who was raised in an isolation chamber because he did not have a functioning immune system. The medical and psychological sequellae of indefinite length long-term protective isolation were sufficiently daunting to discourage its further use. Nevertheless, it is used routinely for short, controlled periods for patients undergoing certain types of chemotherapy and organ transplantation.

Isolation is used for diseases that are transmitted through casual contact or respiratory transmission. Strict isolation is used for highly infectious agents that may travel long distances through the air or be caught from cutaneous contact with sores or secretions. Strict isolation requires restriction to a private room with controlled air flow. Persons entering the room must wear gowns, gloves, and respirators capable of filtering out micron-level particles. Respiratory isolation is used for diseases such as tuberculosis that are spread through the inspiration of infected particles but have only limited spread through contact with wounds or secretions. Respiratory isolation requires the same precautions as strict isolation but without the extensive gowning and gloving. Contact isolation is for diseases that spread by direct contact and limited droplet spread. It requires personal protective measures but not a controlled air supply. [Coleman D. The when and how of isolation. RN. 1987;34:50.]

Strict and respiratory isolation must be meticulously maintained to be effective. Patients may not leave the room without supervision to ensure that they do not remove their respirators. Staff must never break isolation, and visitors must be carefully monitored. The patient rooms must be at negative pressure to doors and hallways. The room air must be exhausted outside, preferably through high- efficiency air particulate air filters. Ultraviolet lights may also be used to reduce the spread of infectious particles. All treatment rooms must meet these isolation standards, including the control of personnel entering and leaving the room. [Drug- resistant TB outbreak highlights need for screening. AIDS Alert. 1991;6:96.] The CDC and the military maintain a few very high- level biohazard isolation and medical facilities for potential cases of unknown new agents or highly dangerous diseases such as the Marburg or Ebola viruses.