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Science Policy and Risk Forums

The ORACBA Risk Forums provide an opportunity for discussion of a broad range of policy-related scientific, and methodological issues concerning risk assessment. Forums are open to all public and private risk assessors.

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Salmonella risks pre-harvest and their importance for food safety

Karin Hoelzer
Pew Charitable Trusts
March 14, 2016

Salmonella can infect livestock and is known to be present on many farms and feedlots in the U.S. This presence in ‘pre-harvest’ environments is a recognized food safety risk. Efforts to eliminate Salmonella from livestock production have been successful in some cases, including, for example, large parts of the Scandinavian pig and poultry sectors. However, minimizing Salmonella in pre-harvest settings poses formidable challenges. Salmonella can be introduced onto premises in numerous ways and the relative importance of different pathways is largely unclear: can persist in the environment for long periods of time; can be challenging to detect due to intermittent shedding; can be particularly difficult to control because serotypes may differ considerably in epidemiology. Various pre-harvest interventions have been designed that may directly target Salmonella, that may favor competition with non-pathogenic bacteria (e.g., probiotics), or that may reduce exposure. While some of these interventions have shown promising results, at least in experimental settings, technological, logistical, economical and regulatory challenges complicate their implementation. Moreover, the value of pre-harvest interventions has remained the subject of intense scientific debate. This presentation will discuss the challenges and promise of pre-harvest interventions for Salmonella, and highlight the importance of risk assessment and risk-based interventions in this context.

When Is Prevalence (based on presence-absence testing) Sufficient To Predict a Reduction in Illnesses in a Microbiological Food Safety Risk Assessment?

Mike Williams
FSIS Office of Public Health and Science
December 10, 2015

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.


Trends in Reported Foodborne Illness in the United States; 1996-2013

September 17, 2015
Sponsored by: ORACBA and National Capital Area Chapter of the Society for Risk Analysis
Mark Powell, ORACBA Risk Scientist

Retrospective review is a key to designing effective food safety measures. The analysis examines trends in the reported incidence of U.S. foodborne illness using both a conventional generalized linear model and penalized B-spline regression. B-spline regression is a semi-parametric, locally-controlled method that makes no assumptions about the form of the trend. To address the sensitivity of B-spline regression to choices about the number and location of join-points called knots, penalized B-spline regression imposes a “roughness” penalty on differences among neighboring B-spline regression coefficients. The optimal degree of smoothing is determined based on statistical model selection criteria (e.g., generalized cross-validation). The result is a flexible, smooth curve that avoids over-fitting the data, while providing a statistical test for trend. The findings indicate a lack of evidence for continuous reduction in foodborne illnesses in the U.S. during 1996-2013.

On Objective Risk

September 15, 2015
Sponsored by: ORACBA and National Capital Area Chapter of the Society for Risk Analysis
Dima Yazji Shamoun, co-author

Objectivity in the science of risk plays a monumental role in the projection of the benefits from health and safety regulations, which constitute the majority of total reported benefits of all federal regulations. Claims concerning the accuracy of regulatory risk assessments have been un-testable so far in that they focus on whether a risk assessment over- or underestimates the risk of exposure to certain hazards; yet such claims rely on an implication that the true level of risk can be known. This presentation proposes moving the debate from the realm of the un-testable to the realm of the testable "process objectivity" of the science of risk. Consistent adherence to a process should yield objective results. There is a sizable body of guidelines and recommendations on sound risk assessment practices produced by the federal government and by various scientific bodies. The proposed process incorporates these guidelines and recommendations and is testable, objective, and—if adhered to consistently—has the potential to shed light on the accuracy of the benefits calculus of major federal health and safety regulations.

Retrospective Analysis of Significant Rules: APHIS Avocado Import Regulations

July 23, 2015
USDA Animal and Plant Inspection Service, Policy and Program Development
Sponsored by: ORACBA and National Capital Area Chapter of the Society for Risk Analysis
Video / Slides

Agencies can benefit from reviewing past regulatory actions to better understand if anticipated outcomes differ from observed outcomes and if there were any unintended consequences of the regulation. APHIS is developing a framework to conduct retrospective analyses of significant rules. Using regulations of avocado imports as a case study, we assess the accuracy of our economic projections concerning domestic production and prices, consumption, and trade. We revisit issues raised in public comments to the proposed rule to assess how we would respond to the issues today, given the additional data that is now available. We anticipate using this framework to look back at additional significant rules to incorporate lessons learned from prior actions for future analyses.

Attend via webinar: Reserve your Webinar seat now at:
Registration URL:
Webinar ID: 153-842-011

Attend in person:  Please register by contacting Jennifer Lohr at or 202-720-8024.
USDA employees may enter the building at the Wing 1 entrance, located directly above the Smithsonian Metro station. All others must bring a valid government picture ID and enter through Wing 3, located on Independence Ave, between 12th and 14th Streets. When exiting the Smithsonian Metro station turn left, the Wing 3 entrance is half way down the block. For escort to the forum, please have guards call Teresa Pickett Wade at 202-720 8022. For further information, contact Linda Abbott 202-690-6056 or mailto:

FDA Risk Modeling Tools for Enhancing Fresh Produce Safety: Modeling the interface between the environment and fresh produce

July 23, 2014
David Oryang, Sherri Dennis and Yuhuan Chen, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration

Presents FDA’s multi-scale efforts to develop risk modeling tools for enhancing fresh produce safety. Two case studies that model the complex interface between the environment and fresh produce will be examined: an agent based produce risk assessment model; and a geospatial risk assessment model.

New Risk Assessment Tools on

July 15, 2014
Clare Narrod, Research Scientist and Risk Analysis  Program Manager and Kyle McKillop, IT Program Manager
Joint Institute for Food Safety and Applied Nutrition (JIFSAN) is a comprehensive on-line resource for the food safety risk analysis community.  The web site is home to a variety of risk assessment models, food safety risk tools and a library of completed risk assessments as well as some unique data sets.  It is operated by the Joint Institute for Food Safety and Applied Nutrition in collaboration with FDA’s Center for Food Safety and Applied Nutrition and USDA’s Food Safety Inspection Service. JIFSAN has been working with a number of colleagues over the last couple of years to develop tools to assist the risk analysis community.  Dr. Narrod and Kyle McKillop will discuss new risk assessment tools recently added to as well as several that are in progress.

Optimal Food Safety Sampling Under a Budget Constraint

September 18, 2013
Mark Powell, ORACBA Risk Scientist

This paper is currently available in the early view on-line version of Risk Analysis (DOI: 10.1111/risa.12054)

Risk Analysis: Advancing Analysis Workshop - Presentations

Mini-2013 SRA
June 18th, 2013
Washington, DC

Analysis to Support Regulations and Metrics Development

Lettuce, enterohemorrhagic E. coli and irrigation water: Application of FDA's iRISK rool for rapid risk assessment to support proposed produce regulation
Yuhuan Chen, Division of Risk Assessment, Office ofAnalytics and Outreach, CFSAN/FDA

Interagency Risk Assessment for L. monocytogenes in Retail Delis
Janell Kause, Scientific Advisor for Risk Assessment, Office of Public Health Science, FSIS, USDA

Quantitative Assessment of the Risk of Listeriosis from Soft-ripened Cheese consumption in the United States and Canada
Régis Pouillot, Division of Risk Assessment, Office of Analytics and Outreach, CFSAN/FDA

Methods for Risk Informed Decision Making

Addressing Chemical Contaminants Without Established Regulatory Limits in Meat, Poultry and Egg Products: the De Minimis Level Approach  
Alexander Domesle, Risk Analyst, Office of Public Health Science, FSIS, USDA

How do you model a "negligible" probability under the WTO Sanitary and Phytosanitary Agreement?
Mark Powell, Risk Acientist, Office of Risk Assessment and Cost-Benefit Analysis, OCE,USDA

Revising Analytical Methods in Response to New Data or Information

Using a systems approach to retrospective regulatory review: quantifying economic impact and potential risk reduction due to cumulative regulatory actions in an agricultural watershed in Washington
Linda Abbott, Director, Office of Risk Assessment and Cost-Benefit Analysis, OCE, USDA

EPA Dietary Exposure Assessment of Pesticides:  Overview and Evaluation of Updated Consumption Data on Commodity Intake and Exposure
Aaron Niman, LT, U.S. Public Health Service, Office of Pesticide Programs, HED, EPA

2012 Risk Forums

05/04/2013 Procedures for the Pesticide evaluation-assessment in the EU, role of EFSA, Dr. Jordi Serratosa, European Food Safety Authority (EFSA)

Science, Policy and Risk Forum, Estimation of cancer risks and benefits associated with a potential increased consumption of fruits and vegetables, Rick Reiss, Principal Scientist, Exponent


Risk versus Hazard – Lessons from Europe, Ragnar Löfstedt, of King’s College of London