Evaluation of suspension array analysis for detection of egg yolk antibodies against Salmonella Enteritidis

Salmonella enterica serovar Enteritidis (SE) is an important source of food-related diarrhoea in humans, and table eggs are considered the primordial source of contamination of the human food chain. Using eggs collected at egg-packing stations as samples could be a convenient strategy to detect colonization of layer flocks. The aim of this study was to evaluate egg yolk anti-Salmonella antibody detection using suspension array analysis. An egg yolk panel from contact-infected and non-colonized laying hens was used for the evaluation. Receiver Operating Characteristic (ROC) curves were generated to define a cut-off value and to assess the overall accuracy of the assay. The diagnostic sensitivity and specificity were estimated by maximum likelihood. Sensitivity was quantified on hen level and on sample level, and also quantified as a function of time since colonization. The area under the ROC curve was estimated at 0.984 (se 0.006, P<0.001). Of all colonized contact-infected hens, 67.6% [95% CI: 46.8, 100] developed an antibody response, which was detectable 17.4 days [14.3, 26.9] after colonization. In total, 98% [95.4, 99.4] of the 'immunopositive' hens had test positive eggs. The overall sensitivity of the immunological test was 66.7% [45.9, 98.7] and the specificity was 98.5% [97.8, 99.1]. This study provided essential parameters for optimizing surveillance programs based on detection of antibodies, and indicates that immunology based on examination of egg yolk gives important information about the Salmonella status of the flock.