title: A scenario tree model for the Canadian Notifiable Avian Influenza Surveillance System and its application to estimation of probability of freedom and sample size determination.
abstract: In 2008, Canada designed and implemented the Canadian Notifiable Avian Influenza Surveillance System (CanNAISS) with six surveillance activities in a phased-in approach. CanNAISS was a surveillance system because it had more than one surveillance activity or component in 2008: passive surveillance; pre-slaughter surveillance; and voluntary enhanced notifiable avian influenza surveillance. Our objectives were to give a short overview of two active surveillance components in CanNAISS; describe the CanNAISS scenario tree model and its application to estimation of probability of populations being free of NAI virus infection and sample size determination. Our data from the pre-slaughter surveillance component included diagnostic test results from 6296 serum samples representing 601 commercial chicken and turkey farms collected from 25 August 2008 to 29 January 2009. In addition, we included data from a sub-population of farms with high biosecurity standards: 36,164 samples from 55 farms sampled repeatedly over the 24 months study period from January 2007 to December 2008. All submissions were negative for Notifiable Avian Influenza (NAI) virus infection. We developed the CanNAISS scenario tree model, so that it will estimate the surveillance component sensitivity and the probability of a population being free of NAI at the 0.01 farm-level and 0.3 within-farm-level prevalences. We propose that a general model, such as the CanNAISS scenario tree model, may have a broader application than more detailed models that require disease specific input parameters, such as relative risk estimates.
authors.affiliation: Canadian Food Inspection Agency, Epidemiology and Surveillance Section, Atlantic Veterinary College, Department of Health Management, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Jette.Christensen@inspection.gc.ca
authors.forename: Jette
authors.initials: J
authors.lastname: Christensen
authors.forename: Henrik
authors.initials: H
authors.lastname: Stryhn
authors.forename: André
authors.initials: A
authors.lastname: Vallières
authors.forename: Farouk
authors.initials: F
authors.lastname: El Allaki
mesh_terms: D000818:Animals; D001717:Birds; D002170:Canada / Q000453:epidemiology; D002645:Chickens; D003657:Decision Making; D005260:Female; D005585:Influenza in Birds / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D008954:Models, Biological; D018571:Sentinel Surveillance / Q000662:veterinary*; D013045:Species Specificity; D014422:Turkeys