Risk factors for Salmonella enteritidis infections in laying hens.

Contamination with SE is an important threat to food safety in egg production. Various risk factors exist for infection with and spreading of SE on a farm. A data set of regularly collected blood samples from hens at the end of lay was available for analysis. Data included information about infection with SE, date of sampling, housing system and flock size and whether there were hens of different ages on the farm or in the house. By using the mentioned data set, our objective was to identify risk factors associated with SE infection in laying hens. Multiple logistic regression was used to assess the contribution of different variables. Results showed that bigger flocks increased the chance of infection with SE in all housing systems. The system with the lowest chance of infection was the cage system with wet manure. An outdoor run increased the chance of infection only at farms with all hens of the same age. The presence of hens of different ages on a farm was a risk factor for deep litter systems only. This resulted in the highest chance of infection for a deep litter system on a farm with hens of different ages. On a farm with all hens of the same age, however, a deep litter system did not increase the chance of infection with SE compared with a cage system. The main risk factors associated with SE infection, therefore, were flock size, housing system, and farm with hens of different ages.