Evaluation of Agricultural Interventions on Human and Poultry-Related Salmonella Enteritidis in British Columbia

A collaborative investigation between public health and animal health led to numerous interventions along the food chain in response to an outbreak of human salmonellosis and increased incidence of Salmonella Enteritidis (SE) among poultry. Incidence of both human and chicken SE decreased substantially in 2012 and 2013 following these interventions. We used time series analysis to assess the impact of three interventions: vaccination of broiler breeder flocks, separation in the hatchery of breeder eggs, and an industry order to stop farm-gate sales of ungraded broiler hatching eggs. Results show a Granger causal association between human SE incidence and SE incidence in chickens 8 months earlier. Among the interventions, separation of breeder flocks showed a consistent and statistically significant association with declining SE incidence in chickens. Our results did not show consistent declines in chicken SE following breeder flock vaccination (live or inactivated vaccine). None of the interventions had statistically significant impacts on human SE incidence. Our results are consistent with a positive effect of certain interventions and also reveal where additional data are needed for a more comprehensive evaluation. Multiple interventions throughout the food chain are best practices when dealing with enteric pathogens; collecting data on the timing and intensity of these interventions allow proper evaluation of their independent and combined effects. Finally, we identify considerations for others interested in undertaking similar evaluations. Ongoing collaborative work between public health and animal health is required to refine strategies for SE control in British Columbia.