Abstract
BackgroundCommunity quarantine is controversial, and the decision to use and prepare for it should be informed by specific quantitative evidence of benefit. Case-study reports on 2002-2004 SARS outbreaks have discussed the role of quarantine in the community in transmission. However, this literature has not yielded quantitative estimates of the reduction in secondary cases attributable to quarantine as would be seen in other areas of health policy and cost-effectiveness analysis.MethodsUsing data from the 2003 Ontario, Canada, SARS outbreak, two novel expressions for the impact of quarantine are presented. Secondary Case Count Difference (SCCD) reflects reduction in the average number of transmissions arising from a SARS case in quarantine, relative to not in quarantine, at onset of symptoms. SCCD was estimated using Poisson and negative binomial regression models (with identity link function) comparing the number of secondary cases to each index case for quarantine relative to non-quarantined index cases. The inverse of this statistic is proposed as the number needed to quarantine (NNQ) to prevent one additional secondary transmission.ResultsOur estimated SCCD was 0.133 fewer secondary cases per quarantined versus non-quarantined index case; and a NNQ of 7.5 exposed individuals to be placed in community quarantine to prevent one additional case of transmission in the community. This analysis suggests quarantine can be an effective preventive measure, although these estimates lack statistical precision.ConclusionsRelative to other health policy areas, literature on quarantine tends to lack in quantitative expressions of effectiveness, or agreement on how best to report differences in outcomes attributable to control measure. We hope to further this discussion through presentation of means to calculate and express the impact of population control measures. The study of quarantine effectiveness presents several methodological and statistical challenges. Further research and discussion are needed to understand the costs and benefits of enacting quarantine, and this includes a discussion of how quantitative benefit should be communicated to decision-makers and the public, and evaluated.
Highlights
In Emerging Infectious Disease from the Global to the Local Perspective Edited by: Davis JR, Lederberg J
We report the inverse of this statistic, interpretable as Number Need to Quarantine (NNQ)
We present several effect measures, including Secondary Case Count Difference (SCCD) and "number needed to quarantine" (NNQ), a novel adaptation of number needed to treat (NNT)
Summary
In Emerging Infectious Disease from the Global to the Local Perspective Edited by: Davis JR, Lederberg J. Case-study reports on 2002-2004 SARS outbreaks have discussed the role of quarantine in the community in transmission This literature has not yielded quantitative estimates of the reduction in secondary cases attributable to quarantine as would be seen in other areas of health policy and cost-effectiveness analysis. Public health agencies need to have weighed evidence of the potential costs and benefits of these manoeuvres before the outbreak of a severe, novel infection [8,9] and to have publicly and widely communicated the importance of planned control measures [6,10] This makes outcome evaluation of modern quarantine activity an important area for research [2,4,6]. When Rt, has a value below1.0, this is evidence that an outbreak is dying out [21]
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