Effectiveness of quarantine. Examine the effectiveness of quarantine as a policy

Question

Effectiveness of quarantine. Examine the effectiveness of quarantine as a policy to prevent an epidemic. To do so, modify the SIR model to include a stock of quarantined individuals.

(i) Assume people are quarantined only after they exhibit symptoms, so the quarantine rate (the rate of inflow to the quarantined population) flows from the infectious population to the quarantined population. Formulate the quarantine rate as follows. Assume it takes a certain period of time, denoted the Quarantine Time, to identify infectious people and move them to a quarantine area. Further, assume only a fraction of the infectious population, denoted the Quarantine Fraction, is identified as infectious and willing or able to be quarantined. Be sure your formulation for the quarantine rate is dimensionally consistent. Assume quarantined individuals recover from the disease with the same average duration of infectivity as those not quarantined.

ii) Quarantined individuals are not completely removed from contact with the rest of the population (during an epidemic of smallpox in 18th century Boston, for example, the sick were quarantined but still permitted to attend church on Sunday). Modify the equation for the infection rate to include the possibility that quarantined people come in contact with susceptibles at a certain rate, denoted the Quarantine Contact Rate. Assume the infectivity of quarantined individuals is the same as that for other infectives. How does the addition of a stock of quarantined individuals alter the feedback structure of the SIR model?

iii) Assume the Quarantine Time is half a day, and use the parameters for the simulation in Figure 9-6 (c = 6, i = 0.25, d = 2, N = 10,000). Assume the quarantine is perfect, so that the Quarantine Contact Rate is zero. Run the model for various values of the Quarantine Fraction and explain the resulting behavior. What fraction of the infectious population must be quarantined to prevent an epidemic? Now assume that the contact rate of quarantined individuals is half the normal contact rate. What fraction must now be sequestered to prevent an epidemic and how fast must people be moved to quarantine once they become infectious? Explore the response to other parameters, including partial immunization of the population. Compare the efficacy of immunization to quarantine in preventing or slowing epidemics. What policy considerations would influence your choice of these policies in different situations?

Explanation / Answer

A quarantine is used to separate and restrict the movement of people; it is a 'a restraint upon the activities or communication of persons or the transport of goods designed to prevent the spread of disease or pests', for a certain period of time.[1] This is often used in connection to disease and illness, such as those who may possibly have been exposed to a communicable disease.[2] The term is often erroneously used to mean medical isolation, which is "to separate ill persons who have a communicable disease from those who are healthy".[3] The word comes from an Italian variant (seventeenth-century Venetian) of 'quaranta giorni', meaning forty days, the period that all ships were required to be isolated before passengers and crew could go ashore during the Black Death plague epidemic.[4] Quarantine can be applied to humans, but also to animals of various kinds, and both as part of border control as well as within a country.

The quarantining of people often raises questions of civil rights, especially in cases of long confinement or segregation from society, such as that of Mary Mallon (aka Typhoid Mary), a typhoid fever carrier who spent the last 24 years and 7 months her life under quarantine.

The purpose of such quarantine-for-decontamination is to prevent the spread of contamination, and to contain the contamination such that others are not put at risk from a person fleeing a scene where contamination is suspect. It can also be used to limit exposure, as well as eliminate a vector.

The first astronauts to visit the Moon were quarantined upon their return at the specially built Lunar Receiving Laboratory.

New developments for quarantine include new concepts in quarantine vehicles such as the ambulance bus, mobile hospitals, and lockdown/invacuation (inverse evacuation) procedures, as well as docking stations for an ambulance bus to dock to a facility that's under lockdown.

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