Semiquantitative assessment of the distribution of Salmonella in the environment of caged layer flocks.

To evaluate a semiquantitative technique for the enumeration of Salmonella in the environment of layer flocks and to compare findings with those of a standard qualitative technique. Samples were taken from faeces, floor dust, dust on cages, feeders and egg belts. After mixing with buffered peptone water, serial dilutions were prepared and culture was performed using pre-enrichment, then plating on semisolid selective and solid isolation media. Comparison with a qualitative pre-enrichment technique indicated a similar sensitivity for both methods despite smaller sample sizes. The numbers of Salmonella detected for a site or sample type did not correlate closely with the prevalence of positive samples. The sensitive detection and quantification of Salmonella in the flock environment is practicable with the technique described. Quantitative data in many cases do not correlate with qualitative findings. The significance of certain environmental factors and interventions in the maintenance and dissemination of Salmonella in poultry houses may be over- or under-represented by prevalence data alone. The technique described allows the issue of poultry house contamination to be examined from a new perspective.