Investigation of the Prevalence and Distribution of Salmonella in United States Feed Mills

Introduction:  Salmonella is an emerging pathogen of public health concern. Each year, Salmonella infections cost the food industry approximately $2.3 billion and 33% of reported cases are associated with beef, poultry, or pork. This pathogen has the ability to persist in the environment for long periods of time and to resist different temperatures and water activity levels. Salmonella presence in feed mill environment is one of the many potential routes for pathogen transmission into the food production chain. Nevertheless, little is known about Salmonella prevalence and association in feed mills environment.

Purpose: The objective of this study was to investigate the prevalence and distribution of Salmonella in feed mills in different locations of United States.

Methods:  Eleven feed mill locations across eight different states were selected for this study and 12 environmental samples were collected within each feed mill representing samples collected from floor dust, equipment surface, worker shoes and finished product. Visits were conducted during the months of October and November 2016. Samples were analyzed following the FSIS guidelines for isolation and identification of Salmonella. Environmental data and associations between factors with pathogen prevalence were analyzed using Stata/SE 12.

Results:  Of a total of 238 samples collected, 66.0% tested Salmonella positive, and among them 69.4% were positive for O group antigens. All sampled feed mills had at least one Salmonella positive location. The percentage of positive samples ranged from 41.7 to 100% across feed mills and from 39.1 to 100% across states. Overall, following production flow, the number of positive samples decreased from the initial processing steps towards the finished product, except for the finished product bin boot, where the feed is stored until shipment. In this site 81.8% of samples tested positive for Salmonella.

Significance:  The results of this study demonstrate the presence of Salmonella in feed mills environment across United States and indicate their potential role as vehicle for pathogen transmission and spread into the food production chain.