Observations on Salmonella contamination of eggs from infected commercial laying flocks where vaccination for Salmonella enterica serovar Enteritidis had been used

Eggs were collected monthly from 12 cage-layer flocks on four farms where Salmonella Enteritidis was present in vaccinated flocks despite vaccination with an S. Enteritidis bacterin. Where possible, hens were also taken for culture at the end of the laying period, and faecal and environmental samples were taken from the laying houses before and after cleaning and disinfection. Twenty-four batches of six egg shells from the 13 652 tested (0.18% [0.11 to 0.26 CI 95 ] single egg equivalent) were positive for S. Enteritidis and 54 (0.40% [0.30 to 0.52 CI 95 ] single egg equivalent) for other serovars. Six batches of 13 640 (0.04% [0.02 to 0.10 CI 95 ] single egg equivalent) egg contents, bulked in six egg pools, contained S. Enteritidis and three batches contained other serovars. In addition three further batches contained S. Enteritidis in both contents and shells, and two other batches contained other serovars in both. The total level of contamination by S. Enteritidis of both contents and shells found in vaccinated flocks was therefore 33 batches/13 682 eggs(0.24% [0.17 to 0.34 CI 95 ] single egg equivalent). The total of contamination for any Salmonella serovar was 92 batches/13 682 eggs (0.68% [0.55 to 0.84 CI 95 ] single egg equivalent). These results contrast with the findings of testing of eggs from three unvaccinated flocks prior to this study where 21 batches of egg shells from a total of 2101 eggs (1.0% [0.63 to 1.56 CI 95 ] single egg equivalent) and six batches of contents from 2051 eggs (0.29% [0.11 to 0.64 CI 95 ] single egg equivalent) were contaminated with S. Enteritidis. S. Enteritidis was found in 67/699 (9.6%) of vaccinated spent hens and 64/562 (11.4%) of bulked fresh faecal samples taken from laying houses. Failure to adequately clean and disinfect laying houses and to control mice appeared to be a common feature on the farms. Résumé Surveillance de la contamination, par Salmonella , des œufs provenant d'un troupeau de pondeuses infectées chez lesquelles la vaccination Salmonella enterica serovar Enteritidis a été réalisée Tous les mois, des œufs ont été collectés dans 12 troupeaux de pondeuses en cage répartis dans quatre élevages, où Salmonella Enteritidis a été isolée malgré la vaccination avec un vaccin inactivé S. Enteritidis. En fonction des possibilités, les pondeuses ont fait l'objet de culture à la fin de la période de ponte et des échantillons de l'environnement et des fèces ont été réalisés dans les bâtiments avant et après ne