A retrospective case-control study of risk factors associated with Salmonella enterica subsp. enterica serovar Enteritidis infections on Dutch broiler breeder farms.

The organized control of Salmonella enterica subsp. enterica serovar Enteritidis (Se) in the Dutch poultry sector aims to prevent vertical transmission by the top-down approach, but its effectiveness is now undermined by the increasing role of horizontal transmission, so that preventive hygiene on the poultry farm gains significant importance. In order to assess the actual level of preventive hygiene and to identify risk factors, an inquiry was held among a representative number of broiler breeder farms. It became evident that the hygiene conditions on Dutch broiler breeder farms can and must be improved. From a matched case-control study, carried out among Se-infected and Se-free farms, the occurrence of Se infection could be explained for about 30% by factors concerning preventive hygiene, the surroundings of the farm and the farm itself. Thus, other factors, not included in the study, may also be important. No particular key factors were found. Preventive hygiene can certainly reduce the infection risk, but only a comprehensive package of measures can do so. The Dutch Product Board for Poultry and Eggs and the Dutch Organization of Poultry Farmers have now agreed to strict hygiene programmes to control horizontal transmission of Se, but these will require considerable technical and financial investments.