Comparison of environmental sampling methods for detecting Salmonella in commercial laying flocks in the UK

To investigate the performance of the Salmonella National Control Programme (NCP) sampling/testing methods in laying flocks of domestic fowl. Eighty-five visits were made to 69 flocks representative of the main production systems (cage, barn and free-range) infected with Salmonella. In each visit, three methodologies were compared: (i) the European Union (EU) baseline survey method (five faeces and two dust samples); (ii) an in-house (Veterinary Laboratories Agency, VLA) 'wet' method that involved collecting 10 dust and 10 faeces samples into jars with buffered peptone water; and (iii) a method involving two samples of pooled faeces and one of dust (cultured as one sample of each type), which has been adopted for the NCP for laying flocks across the EU. The 'wet' method was the most sensitive, and the NCP the least, although individual NCP samples were the most sensitive ones. The apparent lower sensitivity of the NCP method may be compensated by repeated sampling of flocks (twice during rear and several times during lay). Sampling using VLA methodology should be advocated for farms aiming to disclose low-level Salmonella before restrictions on the sale of eggs from Salmonella Enteritidis or Salmonella Typhimurium-infected flocks are in place.