Salmonella Prevalence and Quantification in Market Hog Lymph Nodes and Tonsils in Several Regions and Seasons of the United States

Market hog lymph nodes (LNs) can contaminate carcasses with Salmonella, as well as ground and comminuted pork products. The objective of this study was to perform a qualitative and quantitative analysis of LNs from several regions and seasons in the United States to establish a Salmonella prevalence and concentration baseline. Six types of LNs (axillary, mesenteric, subiliac, tracheobronchial, superficial inguinal, prescapular), and tonsils were sampled from market hog carcasses from different regions (east, central, and west) and seasons (winter, spring, and summer/fall). Salmonella was detected and enumerated using BAX®-System-SalQuant® methods and the BAX®-System Real-Time Salmonella Assay. Salmonella prevalence (N = 4,132) was 36% for tonsils, 35% for mesenteric LN, and less than 10% for the other LN types. Of the 601 carcasses tested, 62% were positive for Salmonella, with the highest prevalence occurring during spring in the east (90.9%), and the lowest prevalence occurring during spring in the central region (26.0%). Tonsil prevalence was greatest in the eastern region during spring. Mesenteric LN prevalence was high (>20%) regardless of season or region. Salmonella prevalence in tracheobronchial, subiliac, axillary, and superficial inguinal LNs was generally greatest during the spring or fall and in the eastern region. The median SalQuant® Salmonella concentration was 2.18 log₁₀ Salmonella cells/sample. Median SalQuant® concentration for all other sample types fell below the limit of quantification (1 log₁₀ Salmonella cells/sample). This longitudinal study can be used by the pork industry for risk assessments and risk-based decision-making.