title: Adapting a scenario tree model for freedom from disease as surveillance progresses: the Canadian notifiable avian influenza model.
abstract: Scenario tree models with temporal discounting have been applied in four continents to support claims of freedom from animal disease. Recently, a second (new) model was developed for the same population and disease. This is a natural development because surveillance is a dynamic process that needs to adapt to changing circumstances - the difficulty is the justification for, documentation of, presentation of and the acceptance of the changes. Our objective was to propose a systematic approach to present changes to an existing scenario tree model for freedom from disease. We used the example of how we adapted the deterministic Canadian Notifiable Avian Influenza scenario tree model published in 2011 to a stochastic scenario tree model where the definition of sub-populations and the estimation of probability of introduction of the pathogen were modified. We found that the standardized approach by Vanderstichel et al. (2013) with modifications provided a systematic approach to make and present changes to an existing scenario tree model. We believe that the new 2013 CanNAISS scenario tree model is a better model than the 2011 model because the 2013 model included more surveillance data. In particular, the new data on Notifiable Avian Influenza in Canada from the last 5 years were used to improve input parameters and model structure.
authors.affiliation: Epidemiology and Surveillance Section, Canadian Food Inspection Agency, Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI C1A 4P3, Canada. Electronic address: Jette.Christensen@inspection.gc.ca.
authors.forename: Jette
authors.initials: J
authors.lastname: Christensen
authors.affiliation: Canadian Food Inspection Agency, 3200 rue Sicotte, C.P. 5000 Saint Hyacinthe, Quebac, Canada.
authors.forename: Farouk
authors.initials: F
authors.lastname: El Allaki
authors.affiliation: Canadian Food Inspection Agency, 3200 rue Sicotte, C.P. 5000 Saint Hyacinthe, Quebac, Canada.
authors.forename: André
authors.initials: A
authors.lastname: Vallières
mesh_terms: D000818:Animals; D001717:Birds; D002170:Canada / Q000453:epidemiology; D018563:Disease Notification; D004196:Disease Outbreaks / Q000662:veterinary; D005585:Influenza in Birds / Q000453:epidemiology*; D008954:Models, Biological; D011159:Population Surveillance; D013997:Time Factors
keywords: Avian influenza; Disease freedom; Poultry; Scenario tree methodology; Scenario tree modeling; Surveillance