No abstract

Increasing demands for cost-effectiveness in surveillance for human health hazards can be met by 1ntroducmg nsk-based principles. This 1mphes target1ng subpopulat1ons w1th h1gher nsk of Infection compared to the whole population. We demonstrate how historical data from surveillance can be used to assess risk of infection. The model is called "Discounting historical evidence" and depends mainly on two variables: Annual risk of introduction Plntro and surveillance system sensitivity SSe (ability to detect infection if present). The model Implies simulations that reiterate for a number of years, and for each year the output is updated with the confidence on absence of infection. Trichmella sp1ralis infect1on in p1gs IS used as an example. In Denmark, pigs at slaughter are tested (currently 23 mill1on per year), and despite of > 70 years of sampling no pigs have been found positive. Hence, we concluded that Plntro 1s low. SSe can be estimated from the maximum number of infected carcasses expected under the spec1fied design prevalence, and the sensitiv1ty of the test applied. According to the assessment, the prevalence of Trichmella in Dan1sh pigs is negligible (<1 case/ million). Based on this , a risk-based surveillance programme for Tnchmella is des1gned that targets all outdoor reared pigs as well as all sows and boars (currently 610,000 per year). Compared to confined pigs, outdoor-reared pigs have higher nsk of getting Tnchinella because of their exposure to wildlife , wh1ch m1ght harbour Tnchmella. Sows and boars are at increased risk, because they live longer than fimshers. Again , SSe and Plntro are estimated and the model is used to show how risk-based surveillance can be applied w1thout jeopardizing human health. Finally, we Incorporate wildlife surveys and test quality assurance in the programme. The model results are included in an application to the European Commission concern1ng Denmark's status as a reg1on w1th negligible risk of Trichinella .