A quantitative risk assessment of Listeria monocytogenes from prevalence and concentration data: Application to a traditional ready to eat (RTE) meat product.

Ready to Eat (RTE) cooked meat products are among the most consumed RTE food subcategories in the EU/EEA. They are also associated with the highest number of identified listeriosis cases per year (>850), thus posing a public health risk especially among the susceptible population. This study estimated the risk of listeriosis from Italian head cheese (Coppa di Testa) consumption using a Quantitative Microbiological Risk Assessment (QMRA) based on data of prevalence and starting concentrations of Listeria monocytogenes in the product during a 3-year period (n = 1568). A consumer survey (n = 162) was conducted to provide information on domestic storage time and consumption habits, and storage conditions were determined from recordings of temperatures of domestic refrigerators (n = 57). A probabilistic model was designed for the evaluation of the growth of L. monocytogenes at each stage of the product pathway from production to consumption, using Monte Carlo simulations and employing the @Risk software. Risks associated to consumption of vacuum-packed and sliced-at-retail head cheese were assessed: The model predicted that the risk of listeriosis per serving of vacuum-packed product was in the 10-4 and 10-6 range (mean) for the high-risk and general populations respectively, and listeriosis cases were estimated to be greater than those due to consumption of sliced product (with risks in the range of 10-7 and 10-8). Overall, the model predicted that the mean number of listeriosis cases ranged from 0.001 to 0.24 and from 0.06 to 10 per one hundred thousand people, for the healthy and the high-risk population, respectively. Scenario analyses indicated that better control of the temperature of domestic refrigerators is effective in reducing the predicted risk of listeriosis for the longer stored vacuum-packed product by ~80 % for both the healthy and high-risk populations, whereas a shorter use-by-date of 30 days is an effective risk mitigation measure for both types of packed product. Model assumptions, as well as data gaps are discussed.

Growth of Listeria monocytogenes in ready-to-eat "shrimp cocktail": Risk assessment and possible preventive interventions.

The present study investigated the presence, growth potential, and public health risk posed by Listeria monocytogenes in a ready-to-eat "shrimp cocktail". The pathogen was detected in 4 out of the 104 samples, and there were no counts above the enumeration limit (1 Log colony-forming unit (CFU)/g); the product was a suitable substrate for pathogen growth owing to its chemical/physical properties. A stochastic quantitative microbial risk assessment (QMRA) was performed to estimate the expected number of invasive listeriosis cases caused by the consumption of 10,000 servings of the product on the last day of its shelf life, considering a population comprising healthy consumers, those susceptible, and transplant recipients. The model predicted no cases for this scenario. Uncertainties were included by considering alternative scenarios; even when considering an increased mean bacterial concentration (up to 3-4 Log CFU/g), no cases were estimated. Following a producer's demand, the exposure assessment model was also used to estimate the probability of the product exceeding the threshold of 2 log CFU/g during the shelf life. The possibility of Listeria growth in the product could not be avoided. Therefore, a modification of the production process was tested to re-classify the product as unsuitable for Listeria growth (EC Reg. 2073/2005). The shrimps were conditioned in three different organic acid solutions comprising: acetic acid (1500 ppm) (A); benzoic acid (1500 ppm) + acetic acid (500 ppm) + lactic acid (750 ppm) (BLA); and lactic acid (4500 ppm) + sodium acetate (2500 ppm) (LSA). Testing was conducted over various treatment durations (1 day-5 days). Treatment for 2 days in the LSA solution was selected based on efficacy, the absence of consumer-perceptible sensorial modifications, and the producers' production rate requirements. The concentration of L. monocytogenes decreased when the new process was applied, which confirmed the usefulness and effectiveness of the treatment relative to the traditional process. Thus, the product obtained by the modified production process did not support the growth of L. monocytogenes.

An Assessment of Listeriosis Risk Associated with a Contaminated Production Lot of Frozen Vegetables Consumed under Alternative Consumer Handling Scenarios.

Frozen foods do not support the growth of Listeria monocytogenes (LM) and should be handled appropriately for safety. However, consumer trends regarding preparation of some frozen foods may contribute to the risk of foodborne listeriosis, specifically when cooking instructions are not followed and frozen products are instead added directly to smoothies or salads. A quantitative microbial risk assessment model FFLLoRA (Frozen Food Listeria Lot Risk Assessment) was developed to assess the lot-level listeriosis risk due to LM contamination in frozen vegetables consumed as a ready-to-eat food. The model was designed to estimate listeriosis risk per serving and the number of illnesses per production lot of frozen vegetables contaminated with LM, considering individual facility factors such as lot size, prevalence of LM contamination, and consumer handling prior to consumption. A production lot of 1 million packages with 10 servings each was assumed. When at least half of the servings were cooked prior to consumption, the median risk of invasive listeriosis per serving in both the general and susceptible population was <1.0 × 10-16 with the median (5th, 95th percentiles) predicted number of illnesses per lot as 0 (0, 0) and 0 (0, 1) under the exponential and Weibull-gamma dose-response functions, respectively. In scenarios in which all servings are consumed as ready-to-eat, the median predicted risk per serving was 1.8 × 10-13 and 7.8 × 10-12 in the general and susceptible populations, respectively. The median (5th, 95th percentile) number of illnesses was 0 (0, 0) and 0 (0, 6) for the exponential and Weibull-Gamma models, respectively. Classification tree analysis highlighted initial concentration of LM in the lot, temperature at which the product is thawed, and whether a serving is cooked as main predictors for illness from a lot. Overall, the FFLLoRA provides frozen food manufacturers with a tool to assess LM contamination and consumer behavior when managing rare and/or minimal contamination events in frozen foods.

Assessment of the bioprotective potential of lactic acid bacteria against Listeria monocytogenes on vacuum-packed cold-smoked salmon stored at 8 °C.

Smoked salmon is a highly appreciated delicatessen product. Nevertheless, this ready-to-eat (RTE) product is considered at risk for Listeria monocytogenes, due to both the prevalence and growth potential of this bacteria on the product. Biopreservation may be considered a mild and natural effective strategy for minimizing this risk. In this study, we evaluated the following three potential bioprotective lactic acid bacterial strains against L. monocytogenes in three smoked salmon types with different physicochemical characteristics, primarily fat, moisture, phenol and acid acetic content: two bacteriocin-like producers that were isolated from smoked salmon and identified as Lactobacillus curvatus and Carnobacterium maltaromaticum and a recognized bioprotective bacteriocin producer from meat origin, Lactobacillus sakei CTC494. L. sakei CTC494 inhibited the growth of L. monocytogenes after 21 days of storage at 8 °C in all the products tested, whereas L. curvatus CTC1742 only limited the growth of the pathogen (<2 log increase). The effectiveness of C. maltaromaticum CTC1741 was dependent on the product type; this strain limited the growth of the pathogen in only one smoked salmon type. These results suggest that the meat-borne starter culture, L. sakei CTC494, may potentially be used as a bioprotective culture to improve the food safety of cold-smoked salmon.

An assessment of food safety information provision for UK chemotherapy patients to reduce the risk of foodborne infection.

OBJECTIVES: Given the increased risk of foodborne infection to cancer patients receiving chemotherapy treatment, and the risk of listeriosis reportedly five-times greater to this immunocompromised patient group, there is a need to ensure the implementation of domestic food safety practices among chemotherapy patients and their family caregivers. However, information regarding the adequacy of resources to inform and enable patients to implement domestic food safety practices to reduce the risk of foodborne infection is limited. Consequently, this study aimed to evaluate the provision of food safety information available to UK chemotherapy patients. STUDY DESIGN: In-depth semi-structured interviews and content analysis of online patient information resources. METHODS: Interviews with patients and family caregivers (n = 15) were conducted to explore food-related experiences during chemotherapy treatment. Online food-related information resources for chemotherapy patients (n = 45) were obtained from 35 of 154 National Health Service chemotherapy providers in England, Scotland, and Wales, the Department of Health (DoH) and three of 184 identified UK cancer charities. Identified food-related information resources were reviewed using a content-analysis approach to assess the inclusion of food safety information for chemotherapy patients. RESULTS: In-depth interviews established that many patients indicated awareness of immunosuppression during treatment. Although patients reported practicing caution to reduce the risk of communicable diseases by avoiding crowded spaces/public transport, food safety was reported to be of minimal concern during treatment and the risk of foodborne infection was often underestimated. The review of online food-related patient information resources established that many resources failed to highlight the increased risk of foodborne infection and emphasize the importance of food safety for patients during chemotherapy treatment. Considerable information gaps exist, particularly in relation to listeriosis prevention practices. Cumulatively, information was inconsistent, insufficient, and varied between resources. CONCLUSION: The study has identified the need for an effective, standardized food safety resource specifically targeting chemotherapy patients and family caregivers. Such intervention is essential to assist efforts in reducing the risks associated with foodborne infection among chemotherapy patients.

The STARTEC Decision Support Tool for Better Tradeoffs between Food Safety, Quality, Nutrition, and Costs in Production of Advanced Ready-to-Eat Foods.

A prototype decision support IT-tool for the food industry was developed in the STARTEC project. Typical processes and decision steps were mapped using real life production scenarios of participating food companies manufacturing complex ready-to-eat foods. Companies looked for a more integrated approach when making food safety decisions that would align with existing HACCP systems. The tool was designed with shelf life assessments and data on safety, quality, and costs, using a pasta salad meal as a case product. The process flow chart was used as starting point, with simulation options at each process step. Key parameters like pH, water activity, costs of ingredients and salaries, and default models for calculations of Listeria monocytogenes, quality scores, and vitamin C, were placed in an interactive database. Customization of the models and settings was possible on the user-interface. The simulation module outputs were provided as detailed curves or categorized as "good"; "sufficient"; or "corrective action needed" based on threshold limit values set by the user. Possible corrective actions were suggested by the system. The tool was tested and approved by end-users based on selected ready-to-eat food products. Compared to other decision support tools, the STARTEC-tool is product-specific and multidisciplinary and includes interpretation and targeted recommendations for end-users.

An educationally inspired illustration of two-dimensional Quantitative Microbiological Risk Assessment (QMRA) and sensitivity analysis.

Quantitative Microbiological Risk Assessment (QMRA) is a structured methodology used to assess the risk involved by ingestion of a pathogen. It applies mathematical models combined with an accurate exploitation of data sets, represented by distributions and - in the case of two-dimensional Monte Carlo simulations - their hyperparameters. This research aims to highlight background information, assumptions and truncations of a two-dimensional QMRA and advanced sensitivity analysis. We believe that such a detailed listing is not always clearly presented in actual risk assessment studies, while it is essential to ensure reliable and realistic simulations and interpretations. As a case-study, we are considering the occurrence of listeriosis in smoked fish products in Belgium during the period 2008-2009, using two-dimensional Monte Carlo and two sensitivity analysis methods (Spearman correlation and Sobol sensitivity indices) to estimate the most relevant factors of the final risk estimate. A risk estimate of 0.018% per consumption of contaminated smoked fish by an immunocompromised person was obtained. The final estimate of listeriosis cases (23) is within the actual reported result obtained for the same period and for the same population. Variability on the final risk estimate is determined by the variability regarding (i) consumer refrigerator temperatures, (ii) the reference growth rate of L. monocytogenes, (iii) the minimum growth temperature of L. monocytogenes and (iv) consumer portion size. Variability regarding the initial contamination level of L. monocytogenes tends to appear as a determinant of risk variability only when the minimum growth temperature is not included in the sensitivity analysis; when it is included the impact regarding the variability on the initial contamination level of L. monocytogenes is disappearing. Uncertainty determinants of the final risk indicated the need of gathering more information on the reference growth rate and the minimum growth temperature of L. monocytogenes. Uncertainty in the dose-response relationship was not included in the analysis, hence the level of its influence cannot be assessed in the present research. Finally, a baseline global workflow for QMRA and sensitivity analysis is proposed.

Health professionals' knowledge and understanding about Listeria monocytogenes indicates a need for improved professional training.

Listeria monocytogenes causes listeriosis, an uncommon but potentially fatal disease in immunocompromised persons, with a public health burden of approximately $2 billion annually. Those consumers most at risk are the highly susceptible populations otherwise known as the immunocompromised. Health professionals have a considerable amount of interaction with the immunocompromised and are therefore a valuable resource for providing appropriate safe food handling information. To determine how knowledgeable health professionals are about Listeria monocytogenes, a nationwide Web-based survey was distributed targeting registered nurses (RNs) and registered dietitians (RDs) who work with highly susceptible populations. Responses were received from 499 health professionals. Knowledge and understanding of Listeria monocytogenes was assessed descriptively. Parametric and nonparametric analyses were used to detect differences between RNs and RDs. The major finding is that there are gaps in knowledge and a self-declared lack of understanding by both groups, but especially RNs, about Listeria monocytogenes. RDs were more likely than RNs to provide information about specific foods and food storage behaviors to prevent a Listeria infection. Notably, neither group of health professionals consistently provided Listeria prevention messages to their immunocompromised patients. Pathogens will continue to emerge as food production, climate, water, and waste management systems change. Health professionals, represented by RNs and RDs, need resources and training to ensure that they are providing the most progressive information about various harmful pathogens; in this instance, Listeria monocytogenes.

Predictive microbiology models vs. modeling microbial growth within Listeria monocytogenes risk assessment: what parameters matter and why.

Predictive microbiology models are essential tools to model bacterial growth in quantitative microbial risk assessments. Various predictive microbiology models and sets of parameters are available: it is of interest to understand the consequences of the choice of the growth model on the risk assessment outputs. Thus, an exercise was conducted to explore the impact of the use of several published models to predict Listeria monocytogenes growth during food storage in a product that permits growth. Results underline a gap between the most studied factors in predictive microbiology modeling (lag, growth rate) and the most influential parameters on the estimated risk of listeriosis in this scenario (maximum population density, bacterial competition). The mathematical properties of an exponential dose-response model for Listeria accounts for the fact that the mean number of bacteria per serving and, as a consequence, the highest achievable concentrations in the product under study, has a strong influence on the estimated expected number of listeriosis cases in this context.

Serovar 4b complex predominates among Listeria monocytogenes isolates from imported aquatic products in China.

Listeria monocytogenes, the causative organism of listeriosis, is primarily transmitted to humans through contaminated food. In this study, we examined 1275 batches of aquatic products imported from 29 countries and found that 36 batches from 8 countries were contaminated by Listeria (2.8%), with L. monocytogenes accounting for 2.6% (33/1275) and L. innocua for 0.2% (3/1275). Of the 23 selected L. monocytogenes isolates (from the 33 identified), 15 (65.2%) were of serovar 4b complex (4b, 4d, or 4e), three (13.0%) of 1/2a or 3a, four (17.4%) of 1/2b or 3b, and one (4.4%) of 1/2c or 3c. Notably, four of the 23 isolates belonged to epidemic clone I (ECI) and another four were associated with epidemic clone II (ECII), two highly clonal 4b clusters responsible for most of the documented listeriosis outbreaks. In the multilocus sequence typing scheme based on the concatenated genes gyrB-dapE-hisJ-sigB-ribC-purM-betL-gap-tuf, serovar 4b complex isolates from imported aquatic products exhibited significant genetic diversity. While the four ECI isolates were genetically related to those from Chinese diseased animals, both lacking one proline-rich repeat of ActA, the four ECII isolates were located between 1/2b or 3b strains. As the L. monocytogenes isolates from imported aquatic products possessed a nearly complete set of major infection-related genes, they demonstrated virulence potential in mouse model.

Use of results of microbiological analyses for risk-based control of Listeria monocytogenes in marinated broiler legs.

Microbial risk assessment provides a means of estimating consumer risks associated with food products. The methods can also be applied at the plant level. In this study results of microbiological analyses were used to develop a robust single plant level risk assessment. Furthermore, the prevalence and numbers of Listeria monocytogenes in marinated broiler legs in Finland were estimated. These estimates were based on information on the prevalence, numbers and genotypes of L. monocytogenes in 186 marinated broiler legs from 41 retail stores. The products were from three main Finnish producers, which produce 90% of all marinated broiler legs sold in Finland. The prevalence and numbers of L. monocytogenes were estimated by Monte Carlo simulation using WinBUGS, but the model is applicable to any software featuring standard probability distributions. The estimated mean annual number of L. monocytogenes-positive broiler legs sold in Finland was 7.2x10(6) with a 95% credible interval (CI) 6.7x10(6)-7.7x10(6). That would be 34%+/-1% of the marinated broiler legs sold in Finland. The mean number of L. monocytogenes in marinated broiler legs estimated at the sell-by-date was 2 CFU/g, with a 95% CI of 0-14 CFU/g. Producer-specific L. monocytogenes strains were recovered from the products throughout the year, which emphasizes the importance of characterizing the isolates and identifying strains that may cause problems as part of risk assessment studies. As the levels of L. monocytogenes were low, the risk of acquiring listeriosis from these products proved to be insignificant. Consequently there was no need for a thorough national level risk assessment. However, an approach using worst-case and average point estimates was applied to produce an example of single producer level risk assessment based on limited data. This assessment also indicated that the risk from these products was low. The risk-based approach presented in this work can provide estimation of public health risk on which control measures at the plant level can be based.

Extracting additional risk managers information from a risk assessment of Listeria monocytogenes in deli meats.

The risk assessment study of Listeria monocytogenes in ready-to-eat foods conducted by the U.S. Food and Drug Administration is an example of an extensive quantitative microbiological risk assessment that could be used by risk analysts and other scientists to obtain information and by managers and stakeholders to make decisions on food safety management. The present study was conducted to investigate how detailed sensitivity analysis can be used by assessors to extract more information on risk factors and how results can be communicated to managers and stakeholders in an understandable way. The extended sensitivity analysis revealed that the extremes at the right side of the dose distribution (at consumption, 9 to 11.5 log CFU per serving) were responsible for most of the cases of listeriosis simulated. For concentration at retail, values below the detection limit of 0.04 CFU/g and the often used limit for L. monocytogenes of 100 CFU/g (also at retail) were associated with a high number of annual cases of listeriosis (about 29 and 82%, respectively). This association can be explained by growth of L. monocytogenes at both average and extreme values of temperature and time, indicating that a wide distribution can lead to high risk levels. Another finding is the importance of the maximal population density (i.e., the maximum concentration of L. monocytogenes assumed at a certain temperature) for accurately estimating the risk of infection by opportunistic pathogens such as L. monocytogenes. According to the obtained results, mainly concentrations corresponding to the highest maximal population densities caused risk in the simulation. However, sensitivity analysis applied to the uncertainty parameters revealed that prevalence at retail was the most important source of uncertainty in the model.

Food safety objectives should integrate the variability of the concentration of pathogen.

The World Trade Organization introduced the concept of appropriate level of protection (ALOP) as a public health target. For this public health objective to be interpretable by the actors in the food chain, the concept of food safety objective (FSO) was proposed by the International Commission on Microbiological Specifications for Foods and adopted later by the Codex Alimentarius Food Hygiene Committee. The way to translate an ALOP into a FSO is still in debate. The purpose of this article is to develop a methodological tool to derive a FSO from an ALOP being expressed as a maximal annual marginal risk. We explore the different models relating the annual marginal risk to the parameters of the FSO depending on whether the variability in the survival probability and in the concentration of the pathogen are considered or not. If they are not, determination of the FSO is straightforward. If they are, we propose to use stochastic Monte Carlo simulation models and logistic discriminant analysis in order to determine which sets of parameters are compatible with the ALOP. The logistic discriminant function was chosen such that the kappa coefficient is maximized. We illustrate this method by the example of the risks of listeriosis and salmonellosis in one type of soft cheese. We conclude that the definition of the FSO should integrate three dimensions: the prevalence of contamination, the average concentration per contaminated typical serving, and the dispersion of the concentration among those servings.

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.

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.

The food safety management system.

A comprehensive food safety strategy involves establishing risk management goals, food safety objectives and, for production systems, performance objectives and performance criteria. The working instructions for each step of the process should be validated for their effect before integration within a specific HACCP plan. The importance of realistic inactivation models to predict the hygienic equivalence of food processing operations is discussed.

Risk assessment strategies for Europe: integrated safety strategy or final product control: Example of Listeria monocytogenes in processed products from pork meat industry.

The European regulation 2160/2003 of November 17th, 2003 clearly shows the European strategy of zoonosis monitoring and control as an integrated approach, including the entire food production chain with a first application to Salmonella control in different animal species. This regulation is the consequence of a risk assessment performed with a "farm to fork" philosophy. European strategy is scarcely different from the American strategy, despite the fact that both were achieved by a quantitative risk assessment, as for instance, in the USA the control of Salmonella in eggs is supposed to be completed by refrigeration. Nevertheless, the EU will still have a final product control approach towards future regulations on microbiological criteria for foodstuffs. The final production monitoring and control with HACCP (93/43/EC) and microbiological criteria is the only one available for L. monocytogenes in foodstuffs. The purpose of this paper is to discuss alternative control strategies for L. monocytogenes in pig production including integrated risk assessment. In France, most of the food-borne outbreaks associated with L. monocytogenes in delicatessen were due to one particular group of strains belonging to serovar 4b and presenting a particular RFLP/PFGE (Restriction Fragment Length Polymorphism/Pulsed Field Gel Electrophoresis) profile. The outbreak itself is always associated with the initial contamination of a RTE ("ready to eat") product and re-contamination by inappropriate handling after cooking. Consequently, in most cases the RTE product is subject to inadequate refrigeration during an excessive shelf-life. The responsibility of the food industry and the consumer is clearly engaged during this scenario of foodborne diseases. The question is how to avoid the introduction of this particular strain of L. monocytogenes in the food chain. In a study we tried to evaluate the risk of pig carcass contamination at slaughterhouse level and to identify the main risk factors associated with the infection of live pigs. In most cases inappropriate cleaning and disinfection of surfaces were associated with the contamination of raw meat, but in some cases the introduction of epidemic strains in the food chain was also associated with primary production. Feeding with soup in piggeries seemed to select a particular microbial ecology associated to L. monocytogenes contamination of live pigs. The possible strategies that may be used to control L. monocytogenes in live pig production are not yet developed sufficiently to be included in the EC regulation but should be discussed in more detail.