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Research article - Peer-reviewed, 2009

Probability of freedom from disease after the first detection and eradication of PRRS in Sweden: Scenario-tree modelling of the surveillance system

Frössling, Jenny; Ågren, Estelle; Eliasson-Selling, Lena; Sternberg Lewerin, Susanna


In July 2007, PRRS was detected for the first time in Sweden. A total of eight positive herds were identified and various measures were taken to eradicate the disease, including restrictions and slaughter of infected herds. Subsequently, both active and passive surveillance activities were undertaken. This study describes stochastic scenario-tree modelling of all the various surveillance system components, to estimate the current probability that Sweden is free from PRRS. The model includes all actions taken after the first positive herd was detected. The surveillance system components included in the model were as follows: investigations undertaken in association with the outbreak, a serological study based on samples collected at slaughter, samples collected in the national PRRS surveillance programme and passive clinical surveillance. The probability of freedom was estimated in time steps of I month, from July to December 2007. After each time step, the calculated posterior probability of freedom from the previous month, combined with the probability of introduction, was used as a prior probability for the next month.The result from the model showed a 99.8% probability that Sweden was free from PRRS at the end of December 2007. The estimated total sensitivity of the surveillance system varied between 81.2% and 94.3% and was highest during the first months after the outbreak. For sensitivity analysis purposes, the model was also applied using higher risks of introduction. However, this did not make considerable difference to the final estimates. (C) 2009 Elsevier B.V. All rights reserved.


PRRS; Scenario-tree model; Surveillance; Sweden; Disease freedom

Published in

Preventive Veterinary Medicine
2009, Volume: 91, number: 2-4, pages: 137-145

    SLU Authors

      • Ågren, Estelle

        • National Veterinary Institute (SVA)
      • UKÄ Subject classification

        Other Veterinary Science

        Publication Identifiers


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