Sensitivity of environmental sampling methods for detecting Salmonella Enteritidis in commercial laying flocks relative to the within-flock prevalence

The objective of this study was to estimate the sensitivity of three different sampling/testing methodologies for the detection of Salmonella Enteriditis in commercial egg-laying flocks relative to the within-flock prevalence. The following methods were compared on 21 farms: (1) The European Union (EU) baseline survey method (five faecal and two dust samples); (2) an in-house method that involved collecting 10 dust and 10 faecal samples into jars with buffered peptone water, and (3) a method involving single samples of pooled faeces and dust that has been adopted as a monitoring method for the National Control Programme across the EU (the NCP method). Testing of individual bird ovaries/oviduct and caeca was carried out on each flock, and the sensitivity of each sampling method was estimated relative to the within-flock prevalence using Bayesian methods. Results showed that the sensitivity of all the sampling methods increased as the within-flock prevalence increased, and that all were more efficient than individual bird sampling for detection of S. Enteriditis in commercial flocks. The in-house method was the most sensitive of the methods compared, with a 98% power to detect a 0.1% prevalence, and the NCP method the least sensitive, with a 93% power to detect a prevalence of 20%.