Observations on the distribution and persistence of Salmonella enterica serovar enteritidis phage type 29 on a cage layer farm before and after the use of competitive exclusion treatment.

1. A continuously occupied cage layer house, which had been linked with a human outbreak of Salmonella Enteritidis PT29, was investigated to assess the distribution of contamination and the options for control. 2. The presence and persistence of Salmonella before and after application of competitive exclusion (CE) treatment was investigated by culturing samples from faeces, the environment, spent hens and eggs, and use of an ELISA to detect egg yolk antibodies. 3. A high prevalence of Salmonella was found in faecal and environmental samples before CE treatment was used but this reduced to minimal levels after treatment. 4. Egg yolk antibody assay suggested that although treated birds showed reduced excretion of Salmonella there was no difference between these and non-treated birds in terms of seroprevalence. 5. Contamination of the egg packing plant disappeared following CE. 6. Chicks and pullets in separate accommodation on site remained Salmonella free throughout despite no precautions being taken to avoid transmission of infection from the laying flock. 7. The rapid and substantial reduction in Salmonella in faeces, birds and the environment following the introduction of CE treatment suggests that further controlled field studies would be justified.