Renata Ivanek

Risk Factors for Microbial Contamination in Fruits and Vegetables at the Preharvest Level: A Systematic Review

The objective of this study was to perform a systematic review of risk factors for contamination of fruits and vegetables with Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 at the preharvest level. Relevant studies were identified by searching six electronic databases: MEDLINE, EMBASE, CAB Abstracts, AGRIS, AGRICOLA, and FSTA, using the following thesaurus terms: L. monocytogenes, Salmonella, E. coli O157 AND fruit, vegetable. All search terms were exploded to find all related subheadings. To be eligible, studies had to be prospective controlled trials or observational studies at the preharvest level and had to show clear and sufficient information on the process in which the produce was contaminated. Of the 3,463 citations identified, 68 studies fulfilled the eligibility criteria. Most of these studies were on leafy greens and tomatoes. Six studies assessed produce contamination with respect to animal host-related risk factors, and 20 studies assessed contamination with respect to pathogen characteristics. Sixty-two studies assessed the association between produce contamination and factors related to produce, water, and soil, as well as local ecological conditions of the production location. While evaluations of many risk factors for preharvest-level produce contamination have been reported, the quality assessment of the reviewed studies confirmed the existence of solid evidence for only some of them, including growing produce on clay-type soil, the application of contaminated or non-pH-stabilized manure, and the use of spray irrigation with contaminated water, with a particular risk of contamination on the lower leaf surface. In conclusion, synthesis of the reviewed studies suggests that reducing microbial contamination of irrigation water and soil are the most effective targets for the prevention and control of produce contamination. Furthermore, this review provides an inventory of the evaluated risk factors, including those requiring more research.

Quantitative risk assessment for Listeria monocytogenes in selected categories of deli meats: impact of lactate and diacetate on listeriosis cases and deaths.

Foodborne disease associated with consumption of ready-to-eat foods contaminated with Listeria monocytogenes represents a considerable pubic health concern. In a risk assessment published in 2003, the U.S. Food and Drug Administration and the U.S. Food Safety and Inspection Service estimated that about 90% of human listeriosis cases in the United States are caused by consumption of contaminated deli meats. In this risk assessment, all deli meats were grouped into one of 23 categories of ready-to-eat foods, and only the postretail growth of L. monocytogenes was considered. To provide an improved risk assessment for L. monocytogenes in deli meats, we developed a revised risk assessment that (i) models risk for three subcategories of deli meats (i.e., ham, turkey, and roast beef) and (ii) models L. monocytogenes contamination and growth from production to consumption while considering subcategory-specific growth kinetics parameters (i.e., lag phase and exponential growth rate). This model also was used to assess how reformulation of the chosen deli meat subcategories with L. monocytogenes growth inhibitors (i.e., lactate and diacetate) would impact the number of human listeriosis cases. Use of product-specific growth parameters demonstrated how certain deli meat categories differ in the relative risk of causing listeriosis; products that support more rapid growth and have reduced lag phases (e.g., turkey) represent a higher risk. Although reformulation of deli meats with growth inhibitors was estimated to reduce by about 2.5- to 7.8-fold the number of human listeriosis cases linked to a given deli meat subcategory and thus would reduce the overall risk of human listeriosis, even with reformulation deli meats would still cause a considerable number of human listeriosis cases. A combination of strategies is thus needed to provide continued reduction of these cases. Risk assessment models such as that described here will be critical for evaluation of different control approaches and to help define the combinations of control strategies that will have the greatest impact on public health.

Temperature-Dependent Expression of Listeria monocytogenes Internalin and Internalin-Like Genes Suggests Functional Diversity of These Proteins among the Listeriae†

ABSTRACT The Listeria monocytogenes genome contains genes encoding several internalins and internalin-like proteins. As L. monocytogenes is present in many environments and can infect numerous, diverse host species, the environmental temperature was hypothesized to be a signal that might affect internalin gene transcription. A subgenomic microarray was used to investigate temperature-dependent transcription of 24 members of the internalin gene family in L. monocytogenes 10403S. The levels of internalin gene transcripts for cells grown at 37°C were compared to the levels of transcripts for cells grown at 16, 30, and 42°C using competitive microarray hybridization, and the results were confirmed by performing quantitative reverse transcriptase PCR for 14 internalin genes. Based on these studies, the internalin genes can be grouped into the following five temperature-dependent categories: (i) four σB-dependent internalin genes (inlC2, inlD, lmo0331, and lmo0610) with the highest levels of transcripts at 16°C and generally the lowest levels of transcripts at 37°C; (ii) three partially PrfA-dependent internalin genes (inlA, inlB, and inlC) with the lowest levels of transcripts at 16°C and the highest levels of transcripts at 37 and 42°C; (iii) four genes (inlG, inlJ, lmo0514, and lmo1290) with the lowest levels of transcripts at 16°C and the highest levels of transcripts at 30 and/or 37°C; (iv) one gene (lmo0327) with the highest levels of transcripts at 16°C and low levels of transcripts at higher temperatures; and (v) 12 internalin genes with no differences in the levels of transcripts at the temperatures used in this study. The temperature-dependent transcription patterns suggest that the relative importance of different internalins varies by environment, which may provide insight into the specific functions of these proteins.

The Cost and Benefit of Listeria Monocytogenes Food Safety Measures

The objectives of this study were to evaluate economic techniques used to determine the cost and benefit of Listeria monocyto-genes control and to estimate the economic optimum of L. monocytogenes food safety measures. The level of food safety measures is optimal if marginal benefit and marginal cost equate. Estimates of benefit and cost of L. monocytogenes food safety measures, from available published literature, are derived from different methods of economic analysis (willingness to pay, cost of illness, cost function, and event study methods). The estimated annual benefit and cost of L. monocytogenes food safety measures range from

Estimating the non-monetary burden of neurocysticercosis in Mexico.

2.3 billion to

Reproduction numbers for infections with free-living pathogens growing in the environment

22 billion and from

Modeling the effect of seasonal variation in ambient temperature on the transmission dynamics of a pathogen with a free-living stage: example of Escherichia coli O157:H7 in a dairy herd.

.01 billion to

The effect of heterogeneous infectious period and contagiousness on the dynamics of Salmonella transmission in dairy cattle

2.4 billion, respectively. The estimated marginal benefit exceeds the estimated marginal cost, which implies that more food safety measures are warranted before the optimal level of L. monocytogenes food safety can be reached. However, due to considerable lack of data, the optimal level of L. monocytogenes food safety measures could not be estimated. When better data become available, this study can serve as a template for estimating the optimal level of food safety. The understanding of the economic optimum of food safety level will contribute to designing a control program that is economical and acceptable for US society.

A mathematical model for the transmission of Salmonella Typhimurium within a grower-finisher pig herd in Great Britain.

Background Neurocysticercosis (NCC) is a major public health problem in many developing countries where health education, sanitation, and meat inspection infrastructure are insufficient. The condition occurs when humans ingest eggs of the pork tapeworm Taenia solium, which then develop into larvae in the central nervous system. Although NCC is endemic in many areas of the world and is associated with considerable socio-economic losses, the burden of NCC remains largely unknown. This study provides the first estimate of disability adjusted life years (DALYs) associated with NCC in Mexico. Methods DALYs lost for symptomatic cases of NCC in Mexico were estimated by incorporating morbidity and mortality due to NCC-associated epilepsy, and morbidity due to NCC-associated severe chronic headaches. Latin hypercube sampling methods were employed to sample the distributions of uncertain parameters and to estimate 95% credible regions (95% CRs). Findings In Mexico, 144,433 and 98,520 individuals are estimated to suffer from NCC-associated epilepsy and NCC-associated severe chronic headaches, respectively. A total of 25,341 (95% CR: 12,569–46,640) DALYs were estimated to be lost due to these clinical manifestations, with 0.25 (95% CR: 0.12–0.46) DALY lost per 1,000 person-years of which 90% was due to NCC-associated epilepsy. Conclusion This is the first estimate of DALYs associated with NCC in Mexico. However, this value is likely to be underestimated since only the clinical manifestations of epilepsy and severe chronic headaches were included. In addition, due to limited country specific data, some parameters used in the analysis were based on systematic reviews of the literature or primary research from other geographic locations. Even with these limitations, our estimates suggest that healthy years of life are being lost due to NCC in Mexico.

Daily Variability of Listeria Contamination Patterns in a Cold-Smoked Salmon Processing Operation

The basic reproduction number ℛ0 for a compartmental disease model is often calculated by the next generation matrix (NGM) approach. When the interactions within and between disease compartments are interpreted differently, the NGM approach may lead to different ℛ0 expressions. This is demonstrated by considering a susceptible–infectious–recovered–susceptible model with free-living pathogen (FLP) growing in the environment. Although the environment could play different roles in the disease transmission process, leading to different ℛ0 expressions, there is a unique type reproduction number when control strategies are applied to the host population. All ℛ0 expressions agree on the threshold value 1 and preserve their order of magnitude. However, using data for salmonellosis and cholera, it is shown that the estimated ℛ0 values are substantially different. This study highlights the utility and limitations of reproduction numbers to accurately quantify the effects of control strategies for infections with FLPs growing in the environment.