Quarantine is the restriction of movement and isolation of well persons who have been exposed to a contagious disease before it is known whether they will become ill. It includes symptom monitoring, instructions on how to wash hands, and possibly the provision of meals and accommodations in a facility away from home (depending on the disease). Quarantine should last no longer than one incubation period from the time of exposure, and it should be applied in ways that respect “due process” for those who are restricted or isolated.

In a public health emergency, there are many situations where quarantine might be needed to contain an outbreak or protect unexposed people from the harms of infection. The practice is ethically justified because it prevents harm, but it must also be implemented carefully to reduce the risks of undesirable effects and harms, including increased risk of infection in congregate quarantine settings and psychological distress for some people.

The most effective quarantine measures will be those that have a high likelihood of reducing transmission in a particular circumstance—i.e., those that are expected to reduce transmissivity significantly above what would be achieved by other control measures, such as symptom monitoring and daily reporting, without limiting movement (low-to-moderate COE). It is also important to keep in mind that the basic reproductive number (R0) of a pathogen may increase dramatically during an outbreak, and therefore any quarantine action might be more effective if it were shorter than the R0 for the disease.