Food Safety Risk Assessment Research Articles

Impact of spiking techniques on the survival of Staphylococcus aureus in artificially contaminated condiments

Tenacity studies are of relevance for microbial food safety risk assessment. Investigations on the survival of microorganisms in food matrices often require an artificial contamination step prior to microbial testing. Artificial contamination of low-moisture foods, like dried culinary herbs and spices, is challenging. In order to investigate the effect of several spiking techniques on the survival of Staphylococcus (S.) aureus in condiments, dried and ground paprika, pepper, and oregano were spiked with S. aureus using four different techniques: (1) aqueous bacteria suspensions were air-dried directly on the condiments; (2) aqueous bacteria suspensions were air-dried on sand, and then added to the condiments; (3) aqueous bacteria suspensions, or (4) bacteria suspended in liquid nutrient media with lyoprotectant were freeze-dried, crushed to powder, and added to the condiments. For each technique-condiment combination, and point in time, three distinct spiked samples (in three flasks) were prepared and stored in a dark environment at 24 ± 2 °C for up to 25 weeks. Cell counts directly after spiking and over storage time were analyzed. For the latter approach, mathematic models were used to fit the survival curve of each technique-condiment combination and to estimate their D-values. Results indicated that the reduction of the initial S. aureus cell counts depended on the applied spiking techniques and the used matrix. For instance, the initial cell counts in oregano were reduced by 0.8 ± 0.1 log10 cfu/g with technique 2 and by 6.1 ± 0.5 log10 cfu/g with technique 1. Technique 1 at the same time reduced the initial cell counts in paprika by only 0.4 ± 0.1 log10 cfu/g. The calculated D-values ranged from 1.3 ± 0.1 days (technique 3) to 120.1 ± 33.4 days (technique 4). The lowest as well as the highest D-value were observed for paprika samples, which emphasized the effect of the spiking technique. Thus, the behavior of bacteria can be strongly influenced by the selection of the spiking technique used for tenacity studies. Therefore, at least two spiking techniques should be considered, if the survival of microorganisms in low moisture food has to be investigated. In favor of high cell counts after drying, techniques 2 and 4 should be considered, as they performed best in our study.

Enterotoxin Gene Profile and Molecular Characterization of Staphylococcus aureus Isolates from Bovine Bulk Milk and Milk Products of Tigray Region, Northern Ethiopia

Staphylococcal food poisoning (SFP) is an important foodborne disease worldwide, and milk and milk products are commonly associated with SFP outbreaks. The objectives of this study were to investigate the distribution of staphylococcal enterotoxin (se) genes in Staphylococcus aureus from raw cow's milk and milk products and to assess their genetic background with the spa typing method. Of the 549 samples (297 bulk milk and 162 milk product samples) collected from Tigray region, Northern Ethiopia, 160 (29.1%) were positive for S. aureus, of which 82 (51%) were found to harbor se genes by a modified multiplex PCR. Nine se genes were identified: sea (n = 12), seb (n = 3), sec (n = 3), sed(n = 4), seg (n = 49), seh (n = 2), sei (n = 40), sej (n = 1), and tsst-1 (n = 24). The classical type of genes accounted for 27%. Of the 82 enterotoxigenic isolates, 41.5 and 12.4% harbored two or more se genes, respectively. The highest gene association was observed between sei and seg, whereas sea and seb were always found together with the new types of se genes. Altogether, 18 genotypes of toxin genes were identified, and 33% of the samples contained > 5 log CFU ml(-1) S. aureus. spa typing identified 22 spa types and three novel spa sequences, which showed the high genetic diversity of the isolates. No apparent relationship was observed between spa type and se genes. Of the 25 spa types, 13 (52%) were from raw milk, 3 (12%) from milk products, and 9 (36%) from both types of sample. Types t314 (20.7%,n = 17), t458 (18.3%, n = 15), and t6218 (9.8%, n= 8) were the most common spa types identified and were widely distributed in three of the eight studied localities. This is the first study from the Tigray region to report the high distribution of enterotoxigenic S. aureus with a diversified genetic background from dairy food. The study may provide valuable data for microbial food safety risk assessment, molecular epidemiology, and phylogenetic studies of S. aureus in Ethiopia.

Virulence and Antibiotic and Heavy Metal Resistance of Vibrio parahaemolyticus Isolated from Crustaceans and Shellfish in Shanghai, China

Vibrio parahaemolyticus can cause serious human seafoodborne gastroenteritis and even death. In this study, we isolated and characterized 208 V. parahaemolyticus strains from 10 species of commonly consumed crustaceans and shellfish available in fish markets in Shanghai, People's Republic of China, in 2014. Most of these aquatic species had not been detected previously. The results revealed an extremely low occurrence of pathogenic V. parahaemolyticus carrying the toxin gene trh (1.9%). However, a high level of resistance to the antibiotics ampicillin (94.2%), rifampin (93.3%), and streptomycin (77.9%) was found. Approximately 74.5% of the isolates had multidrug-resistant phenotypes. Tolerance to the heavy metals Cu(2+), Pb(2+), and Cd(2+) was detected in the majority of antibiotic resistant isolates. The resistance patterns differed depending on the tested samples. The crustaceans Penaeus monodon and Marsupenaeus japonicus harbored more antibiotic-resistant bacteria, whereas the isolates from the crustacean Litopenaeus vannamei and the shellfish Busycon canaliculatus had high tolerance to eight heavy metals tested. In contrast to the wide distribution of multidrug resistance and tolerance to heavy metals, lower percentages of plasmid DNA (22.6%) and SXT/R391-like integrative and conjugative elements (4.8%) were detected in the isolates, suggesting that V. parahaemolyticus in these aquatic species may have adopted some other molecular mechanisms that mediated the high prevalence of resistance determinants. The results of this study support the need for food safety risk assessment of aquatic products.

Training: Basic concepts and methodology of Food Safety Risk Assessment

EFSA Supporting PublicationsVolume 13, Issue 7 1068E Event reportOpen Access Training: Basic concepts and methodology of Food Safety Risk Assessment Podgorica, Montenegro, 30 May – 1 June 2016 European Food Safety Authority, European Food Safety AuthoritySearch for more papers by this author European Food Safety Authority, European Food Safety AuthoritySearch for more papers by this author First published: 22 July 2016 https://doi.org/10.2903/sp.efsa.2016.EN-1068 Question number: EFSA-Q-2014-00877 Disclaimer: The views or positions expressed in this publication do not necessarily represent in legal terms the official position of the European Food Safety Authority (EFSA). EFSA assumes no responsibility or liability for any errors or inaccuracies that may appear. AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume13, Issue7July 20161068E RelatedInformation

Comparison of the Effects of Environmental Parameters on the Growth Variability of Vibrio parahaemolyticus Coupled with Strain Sources and Genotypes Analyses.

Microbial growth variability plays an important role on food safety risk assessment. In this study, the growth kinetic characteristics corresponding to maximum specific growth rate (μmax) of 50 V. parahaemolyticus isolates from different sources and genotypes were evaluated at different temperatures (10, 20, 30, and 37°C) and salinity (0.5, 3, 5, 7, and 9%) using the automated turbidimetric system Bioscreen C. The results demonstrated that strain growth variability increased as the growth conditions became more stressful both in terms of temperature and salinity. The coefficient of variation (CV) of μmax for temperature was larger than that for salinity, indicating that the impact of temperature on strain growth variability was greater than that of salinity. The strains isolated from freshwater aquatic products had more conspicuous growth variations than those from seawater. Moreover, the strains with tlh+/tdh+/trh− exhibited higher growth variability than tlh+/tdh−/trh− or tlh+/tdh−/trh+, revealing that gene heterogeneity might have possible relations with the growth variability. This research illustrates that the growth environments, strain sources as well as genotypes have impacts on strain growth variability of V. parahaemolyticus, which can be helpful for incorporating strain variability in predictive microbiology and microbial risk assessment.

Expertise for the future: learning and training in the area of food safety risk assessment

EFSA depends on a system of scientific panels, working groups and the expertise of its staff to perform its role in providing high-quality scientific opinions through food safety risk assessment. The centralisation of the evaluation at the EU level not only intends to increase efficiency, but also may represent a challenge with regard to maintaining and developing expertise in the areas of food, feed, plant, animal and environmental risk assessment. The food risk assessment requires a multidisciplinary and interdisciplinary approach: excellence in relevant fields of science is a prerequisite, although knowledge of the full risk analysis process, the EU food law, consumer behaviour, international relations and skills in risk communication is also needed. To handle future challenges regarding food safety risk assessment in an ever-changing and increasingly complex environment, the appropriate expertise needs to be identified and a model of specialised and continuous training is required. The state of the art and the future of education in risk assessment are presented. The following issues are put forward in this special issue: new technologies implemented in risk assessment training; current developments in higher education and training on food safety risk assessment and regulatory science in the EU and worldwide; challenges in training on general risk assessment, food safety risk assessment and environmental risk assessment; best practices and techniques; future developments in capacity building for risk assessment training; and the increased need for training of professionals.

Characterizing the concentration of pathogen occurrence across meat and poultry industries

Raw meat and poultry contamination frequency demonstrably varies across establishments within an industry. The degree to which more contaminated establishments contribute to the overall production of contaminated products by the entire industry is rarely explored in quantitative microbial risk assessments. We use Lorenz curves and Gini coefficients to describe the degree of concentration of contamination within the industry for several product-pathogen combinations. The analysis is based on beta distributions fit to Salmonella sampling data for comminuted chicken, comminuted turkey, chicken parts, and comminuted beef and beef carcasses, as well as for Campylobacter in chicken and turkey. We also explore empirically-derived Lorenz curves. Lorenz curves for nine product-pathogen pairs suggest the pattern of contamination ranges from highly dispersed across the industry (e.g., Salmonella-comminuted chicken, Gini=0.19) to highly concentrated within a small part of the industry (e.g., Salmonella-beef carcass pre-chill, Gini=0.77). Generally, an inverse relationship between an industry's average contamination frequency and its Gini coefficient is observed across these examples. Also, illustrative empirical Lorenz curves are biased relative to the fitted curves because of a substantial number of empirical results with point estimates of zero. Large Gini coefficients may suggest that risk management should focus on just that part of the industry with high contamination frequencies, while small Gini coefficients might suggest that risk management should be more dispersed and holistic across the industry. We discuss monitoring Gini coefficients across time, as well as other applications of these methods, as useful adjuncts to food safety risk assessments.

Training Course on Steering an Expert Knowledge Elicitation

EFSA’s scientific expertise and capacity consists of the members of the Scientific Panels, the Scientific Committee, their Working Groups, and the Authority’s own scientific staff as well as the scientists in Member State institutions working with EFSA. The overall objective of this project was to organize and deliver high quality training courses to meet the needs identified by EFSA to implement Expert Knowledge Elicitation (EKE) approach for quantifying uncertainty in food safety risk assessment. As outcome of the project a training course was developed on ‘Steering an Expert KnowledgeElicitation’. The course covered two working days and was conducted three times during the year 2015. The three courses had 73 participants in total, whereof 17 EFSA experts, 50 EFSA Staff and 6 Network members. This report contains a summary of the project, a technical description of the training, the final curriculum, the training materials, results from evaluation of the course by the participants, and recommendations for future training on this subject.

Antibiotic and heavy-metal resistance of Vibrio parahaemolyticus isolated from fresh shrimps in Shanghai fish markets, China.

Vibrio parahaemolyticus is a causative agent of human serious seafood-borne gastroenteritis disease and even death. Shrimps, often eaten raw or undercooked, are an important reservoir of the bacterium. In this study, we isolated and characterized a total of 400 V. parahaemolyticus strains from commonly consumed fresh shrimps (Litopenaeus vannamei, Macrobrachium rosenbergii, Penaeus monodon, and Exopalaemon carinicauda) in Shanghai fish markets, China in 2013–2014. The results revealed an extremely low occurrence of pathogenic V. parahaemolyticus carrying two major toxic genes (tdh and trh, 0.0 and 0.5 %). However, high incidences of antibiotic resistance were observed among the strains against ampicillin (99 %), streptomycin (45.25 %), rifampicin (38.25 %), and spectinomycin (25.50 %). Approximately 24 % of the strains derived from the P. monodon sample displayed multidrug resistant (MDR) phenotypes, followed by 19, 12, and 6 % from the E. carinicauda, L. vannamei, and M. rosenbergii samples, respectively. Moreover, tolerance to heavy metals of Cr3+ and Zn2+ was observed in 90 antibiotic resistant strains, the majority of which also displayed resistance to Cu2+ (93.3 %), Pb2+ (87.8 %), and Cd2+(73.3 %). The pulsed-field gel electrophoresis (PFGE)-based genotyping of these strains revealed a total of 71 distinct pulsotypes, demonstrating a large degree of genomic variation among the isolates. The wide distribution of MDR and heavy-metal resistance isolates in the PFGE clusters suggested the co-existence of a number of resistant determinants in V. parahaemolyticus population in the detected samples. This study provided data in support of aquatic animal health management and food safety risk assessment in aquaculture industry.

Food Safety, Food Fraud, and Food Defense: A Fast Evolving Literature

Intentional food crime is plural in nature in terms of the types of crime and the differing levels of financial gain. Successful models of food crime are dependent on how well the crime has been executed and at what point, or even if, detection actually occurs. The aim of this paper is to undertake a literature review and critique the often contradictory definitions that can be found in the literature in order to compare and contrast existing food crime risk assessment tools and their application. Food safety, food defense, and food fraud risk assessments consider different criteria in order to determine the degree of situational risk for each criteria and the measures that need to be implemented to mitigate that risk. Further research is required to support the development of global countermeasures, that are of value in reducing overall risk even when the potential hazards may be largely unknown, and specific countermeasures that can act against unique risks.

In vitro bioaccessibility of the marine biotoxin okadaic acid in shellfish

Okadaic acid (OA) and their derivatives are marine toxins responsible for the human diarrhetic shellfish poisoning (DSP). To date the amount of toxins ingested in food has been considered equal to the amount of toxins available for uptake by the human body. In this study, the OA fraction released from the food matrix into the digestive fluids (bioaccessibility) was assessed using a static in vitro digestion model. Naturally contaminated mussels (Mytilus galloprovincialis) and donax clams (Donax sp.), collected from the Portuguese coast, containing OA and dinophysistoxin-3 (DTX3) were used in this study. Bioaccessibility of OA total content was 88% and 75% in mussels and donax clams, respectively. Conversion of DTX3 into its parent compound was verified during the simulated digestive process and no degradation of these toxins was found during the process. This is the first study assessing the bioaccessibility of OA-group toxins in naturally contaminated seafood. This study provides relevant new data that can improve and lead to more accurate food safety risk assessment studies concerning these toxins.

Risk Assessment and Management in Food Safety : beyond Presence or Absence of Threshold

Risk Assessment and Management in Food Safety : beyond Presence or Absence of Threshold

Food safety risk assessment for estimating dietary intake of sulfites in the Taiwanese population.

The purpose of this study was to assess the health risk associated with dietary intake of sulfites for Taiwanese general consumers by conducting a total diet study (TDS). We evaluated the exposure of Taiwanese to sulfites in the diet and its associated health risk. This study used a list of 128 food items representing 83% of the total daily diet. Among the 128 food items, 59 items may contain sulfites. Samples of the 59 food items were collected and subjected to chemical analysis to determine the sulfur dioxide concentration. Health risk was assessed by calculating the ratio of exposure level to the acceptable daily intake (ADI) level of the analyte. For high-intake consumers, the HI of sulfites was 19.7% ADI for males over the age of three years at the 95th percentile; whereas for females over the age of 66, the HI was 17.8% ADI. The HI for high-intake consumers was above 10% ADI. This suggests that regulatory actions must be continued and that consumers should be advised to be aware of processed foods with relatively high contamination to avoid excessive exposure.

Next steps to evidence-based food safety risk analysis: opportunities for health technology assessment methodology implementation

Food safety risk analysis and health technology assessment (HTA) are two different paradigms sharing multiple common features. Decision makers in both fields have the responsibility to promote the health of society deciding on intervention opportunities based on disease burden, intervention feasibility, effectiveness and cost, equity and ethical considerations. The evolution of HTA in the last two decades has resulted in the establishment and widespread use of quantitative tools to support and justify evidence-based decisions. In contrast, decision making in the food safety domain is still a qualitative process rendering ad hoc weights to all aspects considered. This review evaluates whether HTA methodology is suitable for quantitative decision support in food safety risk analysis. We conclude that cost-utility analysis (CUA) could better serve the priority settings in food safety risk management than the currently (rarely) applied cost-benefit analysis (CBA), considering either broad resource allocation or specific safety measure decisions. Development of multi-criteria decision analysis tools could help the introduction of consistent and explicit weighting among cost and health impacts, equity and all other relevant aspects. Cost-minimisation and cost-effectiveness analyses would be relevant for ‘threshold’ and ‘as low as reasonably achievable’ approaches to single food safety risk assessments, respectively. Assuming a future widespread use of HTA methodology in the food safety paradigm, a vision of integrated healthcare, food safety and nutritional policy emerges, with the re-evaluation of budgets and resources of these large systems in a rational and socially acceptable way.

Next steps to evidence-based food safety risk analysis: opportunities for health technology assessment methodology implementation

Food safety risk analysis and health technology assessment (HTA) are two different paradigms sharing multiple common features. Decision makers in both fields have the responsibility to promote the health of society deciding on intervention opportunities based on disease burden, intervention feasibility, effectiveness and cost, equity and ethical considerations. The evolution of HTA in the last two decades has resulted in the establishment and widespread use of quantitative tools to support and justify evidence-based decisions. In contrast, decision making in the food safety domain is still a qualitative process rendering ad hoc weights to all aspects considered. This review evaluates whether HTA methodology is suitable for quantitative decision support in food safety risk analysis. We conclude that cost-utility analysis (CUA) could better serve the priority settings in food safety risk management than the currently (rarely) applied cost-benefit analysis (CBA), considering either broad resource allocation or specific safety measure decisions. Development of multi-criteria decision analysis tools could help the introduction of consistent and explicit weighting among cost and health impacts, equity and all other relevant aspects. Cost-minimisation and cost-effectiveness analyses would be relevant for ‘threshold’ and ‘as low as reasonably achievable’ approaches to single food safety risk assessments, respectively. Assuming a future widespread use of HTA methodology in the food safety paradigm, a vision of integrated healthcare, food safety and nutritional policy emerges, with the re-evaluation of budgets and resources of these large systems in a rational and socially acceptable way.

A fuzzy enabled model for aggregative food safety risk assessment in food supply chains

The food industry is under pressure to improve food product safety, implement efficient risk management and rapid response capability, and manage quality ‘from farm to fork’. In this article, a new risk assessment approach is proposed to perform structured analysis of aggregative food safety risk in the food supply chain by using the concepts of fuzzy set theory and analytical hierarchy process. The novelty of this research lies in performing structured risk assessment and establishing an aggregative food safety risk indicator. It provides a single value representing the risk rating which can be effectively employed in incorporating the safety objectives into operations planning. It can function as a part of practical food safety management tool and help managers to understand how the risk changes and transfers in a supply chain. It will therefore improve food safety and quality through integrating the risk control with supply chain management.

The Margin-of-Exposure approach in food safety risk assessment: Acrylamide as an example

The Margin-of-Exposure approach in food safety risk assessment: Acrylamide as an example

Microbiological Food Safety Surveillance in China.

Microbiological food safety surveillance is a system that collects data regarding food contamination by foodborne pathogens, parasites, viruses, and other harmful microbiological factors. It helps to understand the spectrum of food safety, timely detect food safety hazards, and provide relevant data for food safety supervision, risk assessment, and standards-setting. The study discusses the microbiological surveillance of food safety in China, and introduces the policies and history of the national microbiological surveillance system. In addition, the function and duties of different organizations and institutions are provided in this work, as well as the generation and content of the surveillance plan, quality control, database, and achievement of the microbiological surveillance of food safety in China.

CT/EFSA/AFSCO/2012/01 – Specialised training courses on certain aspects of food safety risk assessment for EFSA Panel/Scientific Committee members, open to EFSA scientific staff

EFSA Supporting PublicationsVolume 12, Issue 8 866E External scientific reportOpen Access CT/EFSA/AFSCO/2012/01 – Specialised training courses on certain aspects of food safety risk assessment for EFSA Panel/Scientific Committee members, open to EFSA scientific staff J. Zilliacus, J. Zilliacus Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorA. Hanberg, A. Hanberg Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorA. Hart, A. Hart Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorP.E. Boon, P.E. Boon Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorJ.D. van Klaveren, J.D. van Klaveren Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this author J. Zilliacus, J. Zilliacus Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorA. Hanberg, A. Hanberg Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorA. Hart, A. Hart Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorP.E. Boon, P.E. Boon Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this authorJ.D. van Klaveren, J.D. van Klaveren Institute of Environmental Medicine, Karolinska Institutet, Sweden, The Food and Environment Research Agency, UK and National Institute for Public Health and the Environment, The NetherlandsSearch for more papers by this author First published: 27 August 2015 https://doi.org/10.2903/sp.efsa.2015.EN-866 The present document has been produced and adopted by the bodies identified above as author(s). This task has been carried out exclusively by the author(s) in the context of a contract between the European Food Safety Authority and the author(s), awarded following a tender procedure. The present document is published complying with the transparency principle to which the Authority is subject. It may not be considered as an output adopted by the Authority. The European Food Safety Authority reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors. Published date: 27 August 2015 Question number: EFSA-Q-2012-00327 AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume12, Issue8August 2015866E RelatedInformation

When Are Qualitative Testing Results Sufficient To Predict a Reduction in Illnesses in a Microbiological Food Safety Risk Assessment?

Process models that include the myriad pathways that pathogen-contaminated food may traverse before consumption and the dose-response function to relate exposure to likelihood of illness may represent a "gold standard" for quantitative microbial risk assessment. Nevertheless, simplifications that rely on measuring the change in contamination occurrence of a raw food at the end of production may provide reasonable approximations of the effects measured by a process model. In this study, we parameterized three process models representing different product-pathogen pairs (i.e., chicken-Salmonella, chicken-Campylobacter, and beef-E. coli O157:H7) to compare with predictions based on qualitative testing of the raw product before consideration of mixing, partitioning, growth, attenuation, or dose-response processes. The results reveal that reductions in prevalence generated from qualitative testing of raw finished product usually underestimate the reduction in likelihood of illness for a population of consumers. Qualitative microbial testing results depend on the test's limit of detection. The negative bias is greater for limits of detection that are closer to the center of the contamination distribution and becomes less as the limit of detection is moved further into the right tail of the distribution. Nevertheless, a positive bias can result when the limit of detection refers to very high contamination levels. Changes in these high levels translate to larger consumed doses for which the slope of the dose-response function is smaller compared with the larger slope associated with smaller doses. Consequently, in these cases, a proportional reduction in prevalence of contamination results in a less than proportional reduction in probability of illness. The magnitudes of the biases are generally less for nonscalar (versus scalar) adjustments to the distribution.