On-farm risk factors for Salmonella Enteritidis contamination

Abstract Forty layer farms from 2 states participated in a study to examine the risk factors and incidence of Salmonella Enteritidis from multiple samples, including environmental drag swabs from the bird areas, feed, water, flies, rodents, live rodent traps, and environmental swabs from areas occupied by other livestock. Twenty-four of these farms had between 3,000 and 31,000 bird flocks (medium-sized flocks) and 16 had less than 3,000 birds (small-sized flocks). All were housed in cage-free production systems. Twenty-two farms included outside pasture areas for the birds. Most of the participants had just come under the FDA Egg Rule and had not yet tested their flocks (flocks under 3,000 birds are exempt) for Salmonella Enteritidis. Many, however, obtained their pullets from commercial Salmonella Enteritidis-clean breeder sources hatched in National Poultry Improvement Plan hatcheries. Vaccination against Salmonella Enteritidis was performed on 21 of the 40 farms (combination of live and killed vaccines). Salmonella Enteritidis was detected on 7 out of the 40 farms, primarily in rodents, their feces, or from swabs taken inside live traps. Of these 7 Salmonella Enteritidis-positive farms, 3 farms that had vaccinated their pullets with live Salmonella Typhimurium vaccine and killed-Salmonella Enteritidis vaccine; no Salmonella Enteritidis was isolated from the environmental drag swabs taken from the bird area or from the eggs on these farms. However, on the farms that had not vaccinated for Salmonella Enteritidis, the organism was isolated from 4 environmental drag swabs and 3 egg pools. The last 4 farms had flocks under 3,000 birds. No Salmonella Enteritidis was isolated from any of the samples of feed, flies, water, or swabs taken from other livestock areas. Based on the initial findings in this study, we suggest the 2 most important risk factors for Salmonella Enteritidis contamination inside the bird area and in the eggs in these small- and medium-sized flocks are the presence of infected rodents and the absence of an Salmonella Enteritidis vaccination program.