Homeland Security

Flu Pandemic Mitigation - Quarantine and Isolation

The CDC differentiates between Quarantine and Isolation. Isolation is the separation of a person or group of persons from other people to prevent the spread of infection. A Quarantine is the restriction of activities or limitation of freedom of movement of those presumed exposed to a communicable disease in such a manner as to prevent effective contact with those not so exposed.


Isolation means separation, during the period of communicability, of a person infected with a communicable disease, in a place and under conditions so as to prevent direct or indirect transmission of an infectious agent to others. It may mean extremely limited contact with an ill person who is diagnosed with or suspected of having a communicable disease. The isolation can occur in a hospital setting in a negative airflow room (prevents potentially contaminated air from going back into the hospital) for very infectious airborne diseases. Isolation usually requires health care providers and visitors to use clothing protectors, masks or respirators, goggles and gloves as a means of protecting the visitors but also to protect the patient from exposure to new diseases that their weakened immune system may not be able to overcome.

The degree of viral shedding in flu is directly proportional to the severity of symptoms and height of fever. Therefore, virus is shed to a greater degree by symptomatic individuals as compared with those who are asymptomatic. As a result, isolating the sick might be expected to reduce transmission and therefore slow the spread of disease. But since asymptomatic infected individuals begin shedding virus for at least a day prior to exihibiting symptoms, patient isolation is highly unlikely to halt the spreads of a pandemic.


Quarantine means restrictions, during or immediately prior to a period of communicability, of activities or travel of an otherwise healthy person who likely has been exposed to a communicable disease. The restrictions are intended to prevent disease transmission during the period of communicability in the event the person is infected. This period is commonly known as the "incubation" period of a disease. This means they have been exposed to an individual with a communicable disease and may be developing the disease as well. Some diseases are not communicable until symptoms appear; other diseases may be communicable for hours or days before the person shows any signs of the disease. Quarantine can be accomplished by a variety of means including having the person stay in their own home and avoid contact with others (including family members) to having the person or group of persons stay in a designated facility, to restricting travel out of an impacted area.

While in Quarantine the contact remains separated from others for a specified period (up to 10 days after potential exposure), during which s/he is assessed on a regular basis (in person at least once daily) for signs and symptoms of influenza disease. Persons with fever, respiratory, or other early influenza symptoms require immediate evaluation by a trained healthcare provider. Restrictions may be voluntary or legally mandated; confinement may be at home or in an appropriate facility. Whenever possible, contacts would be quarantined at home. Home quarantine requires the fewest additional resources, although arrangements must still be made for monitoring patients, reporting symptoms, transporting patients for medical evaluation if necessary, and providing essential supplies and services. Home quarantine is most suitable for contacts with a home environment that can meet their basic needs and in which unexposed household members can be protected from exposure. Because onset of symptoms may be insidious, it may be prudent to minimize interactions with household members during the period of quarantine, if feasible. Quarantined persons should minimize interactions with other household members to prevent exposure during the interval between the development and recognition of symptoms. Precautions may include 1) sleeping and eating in a separate room, 2) using a separate bathroom, and 3) appropriate use of personal protective equipment

In extreme circumstances, public heath officials may consider the use of widespread or community-wide quarantine, which is the most stringent and restrictive containment measure. Strictly speaking, "widespread community quarantine" is a misnomer, since "quarantine" refers to separation of exposed persons only and (unlike snow days) usually allows provision of services and support to affected persons. Like snow days, widespread community quarantine involves asking everyone to stay home. It differs from snow days in two respects: 1) It may involve a legally enforceable action, and 2) it restricts travel into or out of an area circumscribed by a real or virtual "sanitary barrier" or "cordon sanitaire" except to authorized persons, such as public heath or healthcare workers.

It is difficult to imagine a quarantine enforcement situation that would require the use of deadly force by police or military agencies. Indeed, the very question of using deadly force in this context illustrates a lack of understanding of quarantine methods. During the recent SARS pandemic, compliance with quarantine was generally quite good in those countries that had to impose it. In addition, complete quarantine is not necessary to stop an epidemic.

DTRA ASCO commissioned a Rand study on the role of the uniformed military in quarantine and natural disasters. It was noted that in one exercise involving use of chemical weapons, local authorities decided to turn incident command over to the military, citing lack of relevant experience. Interestingly, the National Guard also demurred for the same reason. The study did not resolve exactly when, by whom, and under what circumstances military support would be requested. The report indicated that 1) the military would be involved if the base was hit, but under local civilian control outside the gates, and 2) following one international incident (bombing of embassy in Nairobi) military assets arrived on site, but no one could tell them what to do.

National Guard and Reserve personnel train to their purely military mission. Specific training for quarantine enforcement would require development of a detailed mission description and appropriate training courses, and reprioritization of missions so as to afford the time necessary to provide that training. As long as military support is limited to communications, logistics, and engineering, no additional training is necessary. Armed national guardsmen were in evidence in airports and major train stations after 9-11, though mostly for show and it is doubtful if they ever intended to use their weapons. If quarantine were invoked, it might be similarly comforting to see the national guard on duty at supermarkets, banks, and so on, as a very visible indication of continuity of government.

The United States Marines have two different rules of engagement (ROE). The first is "close and secure." This a military action which potentially involves lethal force against the enemy. The second, "close and save," is intended to assume control of a situation and to preserve lives. Thus, some senior military leaders understand they have to change the way they do things. In addition, there are pockets of specialized knowledge within the military. For example, the military police know how to deal with non-military personnel, how to search a car, and so on. Infantry soldiers do not have this range of training and experience.

The US military is required to assist the Red Cross by congressional mandate. For example, the military coordinates closely in efforts to assist in stabilizing refugee situations. The military in general is not geared to do this, but increasing modular medical training for military units is coming into vogue.

Some mathematical models of quarantine for flu show that there must be a nearly perfect degree of limitation of travel to be effective. Other analyses suggest that these measures do not have to be absolute to be effective. Modeling exercises suggest that partial quarantine can be effective in slowing the rate of disease spread, especially when combined with vaccination.

The short incubation period for influenza makes it difficult to identify and quarantine contacts of pandemic influenza-infected persons before they become ill and have spread infection to others. By contrast, the longer incubation periods for smallpox (about 14 days) and SARS (up to 10 days) make this a more effective control strategy for those infections. Consequently, quarantine is unlikely to be an effective measure in controlling pandemic flu.

In general quarantine has been ineffective, at the most postponing epidemics of influenza by a few weeks to 2 months and even the most severe restrictions on travel and trade have gained only a few weeks. The exception was Australia, in 1918, when maritime quarantine was instituted. This delayed the onset of illness in Australia until 1919 when the virus appeared to have lost some of its virulence. The subsequent epidemic was of milder illness but longer duration than in other countries. Nonetheless, 60% of the mortality was in people aged 20-45 years.

Influenza is predicted to be very difficult to control even with 90% quarantining and contact tracing because of the high level of pre-symptomatic transmission. Quarantining and contact tracing for influenza would probably be infeasible because of the very short incubation (2 days) and infectious (3-4 days) periods.

Pandemic flu would probably take about a month to build up from a few to around a thousand cases and then perhaps only 2 to 4 weeks to spread from Asia. Imposing a 90% restriction on air travel might delay the peak of a pandemic wave by only 1 to 2 weeks. On the other hand a 99.9% travel restriction might delay a pandemic wave by 2 months. If there is a substantial seasonal effect on the transmissibility of pandemic flu it might, theoretically, be possible to "buy" enough time to shift what would otherwise have been a winter outbreak to the spring (or a spring outbreak to the summer), when the lower transmissibility would result in a smaller initial outbreak wave.

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