IAFP 2009 Program Book and Abstract Book - AB51

significantly different (P = 0.001) prevalences were observed at the different levels simulated (S1; S2 and S3). At the lowest contamination level (0.01 CFU/g), bags were cross-contaminated sporadically, resulting in very low E. coli O157:H7 populations (≤ 2 CFU/bag) and prevalence levels (< 1%). Significance: Results obtained for the lowest contamination levels (S1) suggest that most sampling plans will not effectively detect E. coli O157:H7 during production. Hence, in the absence of an E. coli kill step, diligent application of sanitizers to the equipment and wash water is recommended to reduce cross contamination during processing. T7-05 Analyzing the Power and Error of Listeria monocytogenes Growth Challenge Studies MARK POWELL US Dept. of Agriculture, Washington, D.C., USA Introduction: Domestic and international food safety policy developments have spurred interest in the design and interpretation of experimental growth challenge studies to determine whether Ready-to-Eat (RTE) foods are able to support growth of L. monocytogenes. Current challenge study protocols apply a fixed acceptance criteria value (i.e., a difference less than a X log increase) to distinguish real growth from quantitative measurement uncertainty but differ markedly in terms of experimental design and the acceptance criteria under which a RTE food is determined not to support L. monocytogenes growth. Purpose: The objective of the study is to analyze that statistical power and type I (false positive) error probability (α) of L. monocytogenes challenge study protocols and alternative acceptance criteria. Methods: Conventional statistical power analysis and Monte Carlo simulation methods are used to analyze the power and type I error of tests of the no-growth hypothesis under alternative true levels of growth. Results: The current protocols differ substantially with respect to the probability of incorrectly determining that growth occurs and the statistical power to detect growth if it does occur. However, applying any fixed acceptance criteria exceedance value (e.g., less than a 0.5 log or 1 log increase) to distinguish real growth from quantitative measurement uncertainty over different experimental designs and/or measurement uncertainty values implies highly inconsistent type I error probabilities. None of the L. monocytogenes growth challenge study designs currently being considered are likely to provide an F-test with α = 0.05 and power ≥ 0.8 to detect a 1 log increase in mean concentration over the entire range of measurement uncertainty values for enumeration of L. monocytogenes reported in food samples in a validation study of ISO Method 11290-2. Significance: Satisfying the conventional experimental design criteria would require a larger sample size, lower measurement uncertainty, or both. T7-06 Geographic Information Systems Mapping of Foodservice Health Code Violations to Assess Risks for Foodborne DSC Illness in Populations of Different Socioeconomic Status VALERIE L. DARCEY and Jennifer J. Quinlan Drexel University, Dept. of Biology, Philadelphia, PA, USA Introduction: Some data suggests that the incidence of foodborne illness may be associated with an individual’s socioeconomic status (SES), but it is unknown why this may occur. In recent years, the ability to associate environmental conditions with geographic locations has improved greatly using Geographic Information Systems (GIS) which allows for the integration and analysis of geographic and tabular data for detection of environmental gradients. Because low SES is often associated with geographic regions, this research investigated whether GIS technology could be used to correlate health code critical violation rates with SES. Purpose: This research used GIS technology to investigate whether community socioeconomic status relates to access to safe food as measured by foodservice critical health code violations. Methods: Publically available health inspection records documenting critical health code violations for 13,485 foodservice locations, collected between 2005 and 2008 in Philadelphia, PA, were analyzed. Using an overlay analysis through GIS, critical violations were plotted over census tracts in Philadelphia, PA. Census tracts (n = 368) were categorized into one of 5 SES categories based on poverty level. Results: Average proportions of population below poverty in different categories were significantly different and ranged from 5.8% to 52.6%. The average rate of critical violations for all foodservice facilities was 0.67 per inspection. 52% of the facilities had zero critical violations. Rates of violations in poverty groups were: 0.83 ± 1.43 (lowest poverty), 0.64 ± 1.25, 0.62 ± 1.02, 0.63 ± 1.00, and 0.69 ± 1.02 (highest poverty) and the differences were found to be statistically significant. These results indicate an association of higher rates of violations with lowest poverty rates. Significance: This study demonstrates the ability to utilize GIS technology to correlate possible food safety risks with geographic data related to demographics of populations. T7-07 Defining Strain-specific Infective Doses Required for the Establishment of a Systemic Listeria monocytogenes DSC Infection ANNA VAN STELTEN, Julie Simpson, Yuhuan Chen, Jenny Scott, William Ross, Richard Whiting, Martin Wiedmann and Kendra Nightingale Colorado State University, Animal Science, Fort Collins, CO, USA Introduction: Listeria monocytogenes is a human foodborne pathogen that may cause severe invasive disease in susceptible individuals. L. monocytogenes utilizes the virulence factor Internalin A (InlA; encoded by inlA) to induce its uptake by non-professional phagocytes that express the human isoform of E-cadherin. At least 18 naturally occurring mutations leading to a premature stop codon (PMSC) in inlA have been identified worldwide and these mutations have been shown to be causally associated with attenuated mammalian virulence. Abstract Book — 51 Technical

IAFP 2009 Program Book and Abstract Book

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