Assessing the sensitivity of egg yolk antibody testing for detecting Salmonella enteritidis infections in laying hens

The identification of infected commercial poultry flocks has become a pivotal component of efforts to reduce the incidence of egg-associated transmission of Salmonella enteritidis to humans. To assess the sensitivity with which testing for specific antibodies in egg yolks can be applied to detect S. enteritidis infection in laying chickens, groups of hens were orally inoculated with either 10(3), 10(5), or 10(7) cfu of a phage type 13a strain of S. enteritidis. Eggs from these hens were collected for 4 wk after inoculation and yolk samples were tested for antibodies to S. enteritidis flagella by ELISA. All hens that were inoculated with 10(7) cfu of S. enteritidis were detected as infected by the egg yolk ELISA when eggs were tested individually, as were up to 66 and 35% of hens inoculated with 10(5) or 10(3) cfu, respectively. Even when yolks from infected hens were diluted 1:10 in yolk from uninfected hens, specific antibodies could still be found in eggs from 31% of hens given 10(7) cfu of S. enteritidis and 13% of hens given 10(3) cfu. These results demonstrate that egg yolk antibody testing can provide a highly sensitive indication of prior exposure to S. enteritidis, and should accordingly be useful for verifying the effectiveness of programs designed to reduce the incidence of S. enteritidis infection in poultry.