National survey of Salmonella prevalence in lymph nodes of sows and market hogs

Rapid Quantitative Method Development for Beef and Pork Lymph Nodes Using BAX® System Real Time Salmonella Assay

The goal of this study was to develop a rapid RT-PCR enumeration method for Salmonella in pork and beef lymph nodes (LNs) utilizing BAX^®-System-SalQuant^® as well as to assess the performance of the methodology in comparison with existing ones. For study one: PCR curve development, pork, and beef LNs (n = 64) were trimmed, sterilized, pulverized, spiked with 0.00 to 5.00 Log CFU/LN using Salmonella Typhimurium, and then homogenized with BAX-MP media. Samples were incubated at 42 °C and tested at several time points using the BAX^®-System-RT-PCR Assay for Salmonella. Cycle-Threshold values from the BAX^®-System, for each Salmonella concentration were recorded and utilized for statistical analysis. For study two: Method comparison; additional pork and beef LNs (n = 52) were spiked and enumerated by (1) 3M™EB-Petrifilm™ + XLD-replica plate, (2) BAX^®-System-SalQuant^®, and (3) MPN. Linear-fit equations for LNs were estimated with recovery times of 6 h and a limit of quantification (LOQ) of 10 CFU/LN. Slopes and intercepts for LNs using BAX^®-System-SalQuant^® when compared with MPN were not significantly different (p < 0.05), while the same parameters for 3M™EB-Petrifilm™ + XLD-replica plate were significantly different (p > 0.05). The results support the capability of BAX^®-System-SalQuant^® to enumerate Salmonella in pork and beef LNs. This development adds support to the use of PCR-based quantification methodologies for pathogen loads in meat products.

Inoculation of Weaned Pigs by Feed, Water, and Airborne Transmission of Salmonella enterica Serotype 4,[5],12:i:

ABSTRACT

Salmonella enterica serotype 4,[5],12:i:- (STM) has become an increasing problem for food safety and has been often detected in swine products. Weanling pigs were exposed to STM-contaminated feed, water, or air to determine possible STM transmission routes. A control group of pigs was included. STM was monitored daily in feces and rectal and nasal swabs. STM colonization was most prevalent in tissues from tonsil, lower intestine, and mesenteric lymph nodes. No differences in lesion severity were observed between inoculated and control pigs. Contaminated feed, water, and aerosolized particles caused infection in weaned pigs; however, no STM colonization was observed in skeletal muscle destined for human consumption. Based on the results from this study, STM contamination in pork products most likely results from cross-contamination of meat by digesta or lymph node tissue during processing.

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Implementation of Visual-Only Swine Inspection in the European Union: Challenges, Opportunities, and Lessons Learned

ABSTRACT

Consumption of contaminated meat and poultry products is a major source of foodborne illness in the United States and globally. Meat inspection procedures, established more than 100 years ago to detect prevailing food safety issues of the time and largely harmonized around the world, do not effectively detect modern hazards and may inadvertently increase food safety risks by spreading contamination across carcasses. Visual-only inspection (VOI) is a significantly different, modernized meat inspection system that is data driven and minimizes physical manipulation of the carcass during inspection. It was developed based on scientific evidence and risk assessment and aims to better control current food safety hazards. In 2014, the European Union (EU) became the first supranational government in the world to require VOI for all swine herds slaughtered in member states that met certain epidemiologic and animal rearing conditions. Here, we review the implementation of this new inspection system with the goal of informing similar modernization efforts in other countries and for other commodities beyond pork. This article reports the results of a literature review and interviews conducted with nine experts in 2018 on the implementation of the EU's 2014 VOI regulation. Challenges, opportunities, and lessons learned about the implementation of the regulation are described for audiences interested in adapting inspection procedures to prevent and detect modern food safety hazards. Overall, implementation of VOI varies within and across member states, and among slaughterhouses of different sizes. This variation is due to disease risk patterns, supply chain conditions, and trade barriers. Before transitioning to a similar risk-based meat inspection system, other countries should consider the following: science-based research agendas to identify what food chain information best predicts herd health and foodborne hazards, regulatory system design that accurately reflects local hazards, and development of targeted VOI educational materials.

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Changes in Salmonella Contamination in Meat and Poultry Since the Introduction of the Pathogen Reduction and Hazard Analysis and Critical Control Point Rule

ABSTRACT

In 1996, the Food Safety and Inspection Service (FSIS) published its pathogen reduction and hazard analysis and critical control point (PR-HACCP) rule. The intention of this program was to reduce microbial contamination on meat, poultry, and egg products. The program was implemented in stages between January 1998 and January 2000, with sampling for Escherichia coli O157:H7 and/or Salmonella in large production establishments beginning in 1998. As the PR-HACCP program begins its third decade, it is reasonable to question whether there have been reductions in the frequency of pathogen-contaminated meat and poultry products reaching consumers. This study summarizes the results for over 650,000 samples collected by FSIS between 2000 and 2018 in slaughter and processing establishments across the United States and compares these results to the roughly 100,000 retail samples collected by the U.S. Food and Drug Administration between 2002 and 2017. The data demonstrate that there has been an overall reduction in the occurrence of Salmonella on meat and poultry products, but the direction and magnitude of change has not been consistent over time or across commodities. Although the available data do not support the identification of causal factors for the observed changes, a historical review of the timing of various factors and policy decisions generates potential hypotheses for the observed changes.

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Interventions Targeting Deep Tissue Lymph Nodes May Not Effectively Reduce the Risk of Salmonellosis from Ground Pork Consumption: A Quantitative Microbial Risk Assessment

The inclusion of deep tissue lymph nodes (DTLNs) or nonvisceral lymph nodes contaminated with Salmonella in wholesale fresh ground pork (WFGP) production may pose risks to public health. To assess the relative contribution of DTLNs to human salmonellosis occurrence associated with ground pork consumption and to investigate potential critical control points in the slaughter-to-table continuum for the control of human salmonellosis in the United States, a quantitative microbial risk assessment (QMRA) model was established. The model predicted an average of 45 cases of salmonellosis (95% CI = [19, 71]) per 100,000 Americans annually due to WFGP consumption. Sensitivity analysis of all stochastic input variables showed that cooking temperature was the most influential parameter for reducing salmonellosis cases associated with WFGP meals, followed by storage temperature and Salmonella concentration on contaminated carcass surface before fabrication. The input variables were grouped to represent three main factors along the slaughter-to-table chain influencing Salmonella doses ingested via WFGP meals: DTLN-related factors, factors at processing other than DTLNs, and consumer-related factors. The evaluation of the impact of each group of factors by second-order Monte Carlo simulation showed that DTLN-related factors had the lowest impact on the risk estimate among the three groups of factors. These findings indicate that interventions to reduce Salmonella contamination in DTLNs or to remove DTLNs from WFGP products may be less critical for reducing human infections attributable to ground pork than improving consumers' cooking habits or interventions of carcass decontamination at processing.