Observations related to the Salmonella EU layer baseline survey in the United Kingdom: follow-up of positive flocks and sensitivity issues.

A follow-on study was carried out on 23 holdings identified as Salmonella positive in the 2004/2005 European Union (EU) baseline survey of Salmonella in laying hens. Eleven of 13 cage and 4/7 floor houses remained positive for Salmonella when the new flock was tested, and from 10/13 cage and 3/7 floor houses a Salmonella of the same serovar/phage type as found in the EU survey was isolated. There was a high correlation between the level of contamination in the houses at the time of the EU survey and in the follow-on flock. On seven occasions the house identified as positive in the EU survey was sampled after cleaning and disinfection but before a new flock was placed, and in all of them Salmonella could be isolated from the houses. The observed number of infected houses in infected holdings suggests that the holding-level prevalence in the United Kingdom would be about 21% higher than the results obtained in the EU survey.