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The aim of this study is to identify general properties of emerging infectious agents that determine the likely success of two simple public health measures in controlling outbreaks, namely (i) isolating symptomatic individuals and (ii) tracing and quarantining their contacts. Because these measures depend on the recognition of specific disease symptoms, we investigate the relative timing of infectiousness and the appearance of symptoms by using a mathematical model. We show that the success of these control measures is determined as much by the proportion of transmission occurring prior to the onset of overt clinical symptoms (or via asymptomatic infection) as the inherent transmissibility of the etiological agent (measured by the reproductive number R(0)). From published studies, we estimate these quantities for two moderately transmissible viruses, severe acute respiratory syndrome coronavirus and HIV, and for two highly transmissible viruses, smallpox and pandemic influenza. We conclude that severe acute respiratory syndrome and smallpox are easier to control using these simple public health measures. Direct estimation of the proportion of asymptomatic and presymptomatic infections is achievable by contact tracing and should be a priority during an outbreak of a novel infectious agent.

Original publication

DOI

10.1073/pnas.0307506101

Type

Journal article

Journal

Proceedings of the National Academy of Sciences of the United States of America

Publication Date

07/04/2004

Volume

101

Pages

6146 - 6151

Addresses

Department of Infectious Disease Epidemiology, Imperial College, St. Mary's, London W2 1PG, United Kingdom. c.fraser@imperial.ac.uk

Keywords

Humans, Communicable Diseases, Emerging, Virus Diseases, Patient Isolation, Disease Outbreaks, Models, Theoretical