Peter Cowen

Consumer Phase Risk Assessment for Listeria Monocytogenes in Deli Meats

The foodborne disease risk associated with the pathogen Listeria monocytogenes has been the subject of recent efforts in quantitative microbial risk assessment. Building upon one of these efforts undertaken jointly by the U.S. Food and Drug Administration and the U.S. Department of Agriculture (USDA), the purpose of this work was to expand on the consumer phase of the risk assessment to focus on handling practices in the home. One-dimensional Monte Carlo simulation was used to model variability in growth and cross-contamination of L. monocytogenes during food storage and preparation of deli meats. Simulations approximated that 0.3% of the servings were contaminated with >10(4) CFU/g of L. monocytogenes at the time of consumption. The estimated mean risk associated with the consumption of deli meats for the intermediate-age population was approximately 7 deaths per 10(11) servings. Food handling in homes increased the estimated mean mortality by 10(6)-fold. Of all the home food-handling practices modeled, inadequate storage, particularly refrigeration temperatures, provided the greatest contribution to increased risk. The impact of cross-contamination in the home was considerably less. Adherence to USDA Food Safety and Inspection Service recommendations for consumer handling of ready-to-eat foods substantially reduces the risk of listeriosis.

Consumer knowledge, storage, and handling practices regarding Listeria in frankfurters and deli meats : Results of a web-based survey

Proper storage and handling of refrigerated ready-to-eat foods can help reduce the risk of listeriosis. A national Web-based survey was conducted to measure consumer awareness and knowledge of Listeria and to estimate the prevalence of the U.S. Department of Agriculture-recommended consumer storage and handling practices for frankfurters and deli meats. The demographic characteristics of consumers who are unaware of Listeria and who do not follow the recommended storage guidelines were also assessed. In addition, predictive models were developed to determine which consumers engage in risky storage practices. Less than half of the consumers surveyed were aware of Listeria, and most of those aware were unable to identify associated food vehicles. Awareness was lower among adults 60 years of age and older, an at-risk population for listeriosis, and individuals with relatively less education and lower incomes. Most households safely stored and prepared frankfurters. Most households stored unopened packages of vacuum-packed deli meats in the refrigerator within the U.S. Department of Agriculture-recommended storage guidelines (< or =14 days); however, many stored opened packages of vacuum-packed deli meats and freshly sliced deli meats for longer than the recommended time (< or =5 days). Men, more-educated individuals, and individuals living in metropolitan areas were more likely to engage in risky storage practices. This study identified the need to develop targeted educational initiatives on listeriosis prevention.

Sensitivity analysis of Salmonella enteritidis levels in contaminated shell eggs using a biphasic growth model.

Salmonella enteritidis (SE) is a common foodbome pathogen, the transmission of which is primarily associated with the consumption of contaminated Grade A shell eggs. In order to estimate the level of SE present in raw shell eggs, it is necessary to consider the protective effects of the egg albumin, which effectively inhibits SE growth in a time- and temperature-dependent manner. In this study, a SE growth model was produced by combining two mathematical equations that described both the extended lag phase of SE growth (food component) and a SE growth model (pathogen component). This biphasic growth model was then applied to various egg handling scenarios based on the farm-to-table continuum, including in-line and off-line processing facilities with consideration of key events in production, processing, transportation, and storage. Seasonal effects were also studied. Monte Carlo simulation was used to characterize variability in temperature and time parameter values influencing the level of SE to which individuals are exposed. The total level of SE consumed was estimated under best, most likely, and time-temperature abusive handling scenarios. The model estimated that, in most cases, there was no SE growth in contaminated eggs handled under most likely practices, because 10-70% of the yolk membrane remained intact. Under abusive handling scenarios, complete loss of yolk membrane integrity frequently occurred by the time eggs reach the distribution phase, followed by subsequent SE growth, which was often quite rapid. In general, the effect of season and processing method (in-line vs. off-line) was minimal. Further sensitivity analysis demonstrated that the initial SE contamination level significantly influenced the final exposure levels only under no-abuse or mildly abusive conditions. The results of our study suggest that, for maximum reduction of SE exposure level, cooling strategies should not only focus on the on-farm or processing phases, but should emphasize the importance of cooling strategies at the distribution and consumer phases of the farm-to-fork continuum.

A weighted composite dose-response model for human salmonellosis.

This article describes the development of a weighted composite dose-response model for human salmonellosis. Data from previously reported human challenge studies were categorized into two different groups representing low and moderately virulent/pathogenic Salmonella strains based on a disease end point. Because epidemiological data indicate that some Salmonella strains are particularly pathogenic, and in the absence of human feeding study data for such strains, Shigella dysenteriae was used as a proxy for highly virulent strains. Three single-hit dose-response models were applied to the human feeding study data and evaluated for best fit using maximum likelihood estimation: (1) the exponential (E-1pop), (2) the two-subpopulation exponential (E-2pop), and (3) the Beta-Poisson (BP). Based on the goodness-of-fit test, the E-1pop and BP were the best-fit models for low and moderately virulent/pathogenic Salmonella strains, and the E-2pop and BP models were better for highly virulent/pathogenic strains. Epistemic analysis was conducted by determining the degree of confidence associated with the selected models, which was found to be 50%/50% (E-1pop/BP) for low and moderately pathogenic Salmonella strains, and 9.8%/90.2% (E-2pop/BP) for highly virulent strains. The degree of confidence for each component model and variations in the proportion of strains within each virulence/pathogenicity category were incorporated into the overall composite model. This study describes the influence of variation in strain virulence and host susceptibility on the shape of the population dose-response relationship.

Consumer-phase Salmonella enterica serovar enteritidis risk assessment for egg-containing food products

We describe a one-dimensional probabilistic model of the role of domestic food handling behaviors on salmonellosis risk associated with the consumption of eggs and egg-containing foods. Six categories of egg-containing foods were defined based on the amount of egg contained in the food, whether eggs are pooled, and the degree of cooking practiced by consumers. We used bootstrap simulation to quantify uncertainty in risk estimates due to sampling error, and sensitivity analysis to identify key sources of variability and uncertainty in the model. Because of typical model characteristics such as nonlinearity, interaction between inputs, thresholds, and saturation points, Sobols method, a novel sensitivity analysis approach, was used to identify key sources of variability. Based on the mean probability of illness, examples of foods from the food categories ranked from most to least risk of illness were: (1) home-made salad dressings/ice cream; (2) fried eggs/boiled eggs; (3) omelettes; and (4) baked foods/breads. For food categories that may include uncooked eggs (e.g., home-made salad dressings/ice cream), consumer handling conditions such as storage time and temperature after food preparation were the key sources of variability. In contrast, for food categories associated with undercooked eggs (e.g., fried/soft-boiled eggs), the initial level of Salmonella contamination and the log10 reduction due to cooking were the key sources of variability. Important sources of uncertainty varied with both the risk percentile and the food category under consideration. This work adds to previous risk assessments focused on egg production and storage practices, and provides a science-based approach to inform consumer risk communications regarding safe egg handling practices.

Management differences and dairy results.

In representing dairy production as a function of herd management decisions, veterinarians and animal scientists have generally neglected variations in worker performance. This article presents a model that includes organization and personnel management as determinants of dairy operational results. Herd production and manager interview data from 87 farms in Tulare County, California, indicated that these management factors are related to both milk output and herd reproduction efficiency. Manager assumptions about worker motivation, regularity of employee performance feedback, and use of records explained significant variation in fat corrected milk production, somatic cell count, average days open, and services per conception. The study suggests that greater attention to organizational and personnel management could improve results of dairies as well as other agricultural businesses.

Second-order modeling of variability and uncertainty in microbial hazard characterization

This study describes an analytical framework that permits quantitative consideration of variability and uncertainty in microbial hazard characterization. Second-order modeling that used two-dimensional Monte Carlo simulation and stratification into homogeneous population subgroups was applied to integrate uncertainty and variability. Specifically, the bootstrap method was used to simulate sampling error due to the limited sample size in microbial dose-response modeling. A data set from human feeding trials with Campylobacter jejuni was fitted to the log-logistic dose-response model, and results from the analysis of FoodNet surveillance data provided further information on variability and uncertainty in Campylobacter susceptibility due to the effect of age. Results of our analyses indicate that uncertainty associated with dose-response modeling has a dominating influence on the analytical outcome. In contrast, inclusion of the age factor has a limited impact. While the advocacy of more closely modeling variability in hazard characterization is warranted, the characterization of key sources of uncertainties and their consistent propagation throughout a microbial risk assessment actually appear of greater importance.

Preparedness and Disaster Response Training for Veterinary Students: Literature Review and Description of the North Carolina State University Credentialed Veterinary Responder Program

The nations veterinary colleges lack the curricula necessary to meet veterinary demands for animal/public health and emergency preparedness. To this end, the authors report a literature review summarizing training programs within human/veterinary medicine. In addition, the authors describe new competency-based Veterinary Credential Responder training at North Carolina State University College of Veterinary Medicine (NCSU CVM). From an evaluation of 257 PubMed-derived articles relating to veterinary/medical disaster training, 14 fulfilled all inclusion requirements (nine were veterinary oriented; five came from human medical programs). Few offered ideas on the core competencies required to produce disaster-planning and response professionals. The lack of published literature in this area points to a need for more formal discussion and research on core competencies. Non-veterinary articles emphasized learning objectives, commonly listing an incident command system, the National Incident Management System, teamwork, communications, and critical event management/problem solving. These learning objectives were accomplished either through short-course formats or via their integration into a larger curriculum. Formal disaster training in veterinary medicine mostly occurs within existing public health courses. Much of the literature focuses on changing academia to meet current and future needs in public/animal health disaster-preparedness and careers. The NCSU CVM program, in collaboration with North Carolina Department of Agriculture and Consumer Service, Emergency Programs and University of North Carolina at Chapel Hill School of Public Health, operates as a stand-alone third-year two-week core-curriculum training program that combines lecture, online, experiential, and group exercises to meet entry-level federal credentialing requirements. The authors report here its content, outcomes, and future development plans.

Effect of superovulation on lactating Holsteins

Abstract Development of more profitable cows is a primary objective of the dairy cattle breeder. Although embryo transfer technology has progressed, there is still much to be done to improve procedures and management of the donor cow. In this retrospective study, 30 cows were evaluated for the effects of superovulation on reproductive efficiency and on the 305-d lactation curve. Thirty cows (flush group) were superovulated with follicle stimulating hormone (FSH) administered twice daily by intramuscular injections. Cows were flushed one time in the earlier part of the lactation — mean days in milk at flush is 88.4 - and brought back to the regular breeding program when determined ready to breed. Thirty cows with the same parturition date and lactation number were selected as the control group. There was a significant difference in days open, services per conception, and days to first service or flush between groups. Second degree polynomial regressions for the 305-d lactation curve were not different between flushed cows and controls. However, comparing the flush and control groups reveals a significant difference in the milk weight declines (by group) between that on the Dairy Herd Improvement monthly test day before flushing and that on each of the subsequent two test days.