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Global and regional standards for the demonstration of freedom from FMD often include a mandatory waiting period. More recently, the probability of freedom has been used as a quantitative standard for surveillance. This is the population-level analogy of the negative predictive value of a test on an individual animal, and can be calculated from the surveillance sensitivity using a Bayesian approach. In addition to the above factors, the probability of freedom takes further factors into account: the combined sensitivity of multiple surveillance activities (e.g. sero-surveillance and clinical surveillance), the probability of re-introduction of disease per unit time (i.e. biosecurity measures in place), and the accumulation of surveillance evidence over time. The ability to quantitatively capture time-related aspects of the probability of freedom provides a mechanism to evaluate appropriate waiting periods for FMD freedom. This paper illustrates the use of this approach, providing examples of how the appropriate waiting periods may be calculated, based on different approaches to eradication and surveillance.
(c) A. Cameron / EuFMD (email@example.com)