title: An IDEA for short term outbreak projection: nearcasting using the basic reproduction number.
abstract: BACKGROUND
  Communicable disease outbreaks of novel or existing pathogens threaten human health around the globe. It would be desirable to rapidly characterize such outbreaks and develop accurate projections of their duration and cumulative size even when limited preliminary data are available. Here we develop a mathematical model to aid public health authorities in tracking the expansion and contraction of outbreaks with explicit representation of factors (other than population immunity) that may slow epidemic growth.
  
  
  METHODS
  The Incidence Decay and Exponential Adjustment (IDEA) model is a parsimonious function that uses the basic reproduction number R0, along with a discounting factor to project the growth of outbreaks using only basic epidemiological information (e.g., daily incidence counts).
  
  
  RESULTS
  Compared to simulated data, IDEA provides highly accurate estimates of total size and duration for a given outbreak when R0 is low or moderate, and also identifies turning points or new waves. When tested with an outbreak of pandemic influenza A (H1N1), the model generates estimated incidence at the i+1(th) serial interval using data from the i(th) serial interval within an average of 20% of actual incidence.
  
  
  CONCLUSIONS
  This model for communicable disease outbreaks provides rapid assessments of outbreak growth and public health interventions. Further evaluation in the context of real-world outbreaks will establish the utility of IDEA as a tool for front-line epidemiologists.
authors.affiliation: The Dalla Lana School of Public Health, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada ; Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada ; The Decision Centre for Infectious Disease Epidemiology (DeCIDE), Toronto, Ontario, Canada.
authors.forename: David N
authors.initials: DN
authors.lastname: Fisman
authors.affiliation: Department of Psychiatry, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Tanya S
authors.initials: TS
authors.lastname: Hauck
authors.affiliation: The Dalla Lana School of Public Health, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada ; The Decision Centre for Infectious Disease Epidemiology (DeCIDE), Toronto, Ontario, Canada.
authors.forename: Ashleigh R
authors.initials: AR
authors.lastname: Tuite
authors.affiliation: The Dalla Lana School of Public Health, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada ; The Decision Centre for Infectious Disease Epidemiology (DeCIDE), Toronto, Ontario, Canada ; Modeling and Projection Section of the Professional Guidelines and Public Health Practice Division, Centre for Communicable Diseases and Infection Control, Public Health Agency of Canada, Toronto, Ontario, Canada.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Greer
mesh_terms: D050936:Basic Reproduction Number / Q000706:statistics & numerical data*; D003141:Communicable Diseases / Q000453:epidemiology*; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005544:Forecasting / Q000379:methods; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology; D015233:Models, Statistical; D020957:Nunavut / Q000453:epidemiology