Quantitative microbial risk assessment for Escherichia coli O157 on lettuce, based on survival data from controlled studies in a climate chamber

Quantitative risk assessment-epidemic curve prediction model for leafy green outbreak investigation

The objective of this study was to leverage quantitative risk assessment to investigate possible root cause(s) of foodborne illness outbreaks related to Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) infections in leafy greens in the United States. To this end, we developed the FDA leafy green quantitative risk assessment epidemic curve prediction model (FDA-LG QRA-EC) that simulated the lettuce supply chain. The model was used to predict the number of reported illnesses and the epidemic curve associated with lettuce contaminated with STEC O157 for a wide range of scenarios representing various contamination conditions and facility processing/sanitation practices. Model predictions were generated for fresh-cut and whole lettuce, quantifying the differing impacts of facility processing and home preparation on predicted illnesses. Our model revealed that the timespan (i.e., number of days with at least one reported illness) and the peak (i.e., day with the most predicted number of reported illnesses) of the epidemic curve of a STEC O157-lettuce outbreak were not strongly influenced by facility processing/sanitation practices and were indications of contamination pattern among incoming lettuce batches received by the facility or distribution center. Through comparisons with observed number of illnesses from recent STEC O157-lettuce outbreaks, the model identified contamination conditions on incoming lettuce heads that could result in an outbreak of similar size, which can be used to narrow down potential root cause hypotheses.

Predictive Population Dynamics of Escherichia coli O157:H7 and Salmonella enterica on Plants: a Mechanistic Mathematical Model Based on Weather Parameters and Bacterial State

Weather affects key aspects of bacterial behavior on plants but has not been extensively investigated as a tool to assess risk of crop contamination with human foodborne pathogens. A novel mechanistic model informed by weather factors and bacterial state was developed to predict population dynamics on leafy vegetables and tested against published data tracking Escherichia coli O157:H7 (EcO157) and Salmonella enterica populations on lettuce and cilantro plants. The model utilizes temperature, radiation, and dew point depression to characterize pathogen growth and decay rates. Additionally, the model incorporates the population level effect of bacterial physiological state dynamics in the phyllosphere in terms of the duration and frequency of specific weather parameters. The model accurately predicted EcO157 and S. enterica population sizes on lettuce and cilantro leaves in the laboratory under various conditions of temperature, relative humidity, light intensity, and cycles of leaf wetness and dryness. Importantly, the model successfully predicted EcO157 population dynamics on 4-week-old romaine lettuce plants under variable weather conditions in nearly all field trials. Prediction of initial EcO157 population decay rates after inoculation of 6-week-old romaine plants in the same field study was better than that of long-term survival. This suggests that future augmentation of the model should consider plant age and species morphology by including additional physical parameters. Our results highlight the potential of a comprehensive weather-based model in predicting contamination risk in the field. Such a modeling approach would additionally be valuable for timing field sampling in quality control to ensure the microbial safety of produce. IMPORTANCE Fruits and vegetables are important sources of foodborne disease. Novel approaches to improve the microbial safety of produce are greatly lacking. Given that bacterial behavior on plant surfaces is highly dependent on weather factors, risk assessment informed by meteorological data may be an effective tool to integrate into strategies to prevent crop contamination. A mathematical model was developed to predict the population trends of pathogenic E. coli and S. enterica, two major causal agents of foodborne disease associated with produce, on leaves. Our model is based on weather parameters and rates of switching between the active (growing) and inactive (nongrowing) bacterial state resulting from prevailing environmental conditions on leaf surfaces. We demonstrate that the model has the ability to accurately predict dynamics of enteric pathogens on leaves and, notably, sizes of populations of pathogenic E. coli over time after inoculation onto the leaves of young lettuce plants in the field.

Assessment of microbial risk during Australian industrial practices for Escherichia coli O157:H7 in fresh cut-cos lettuce: A stochastic quantitative approach

Escherichia coli O157:H7 risk associated with the consumption of fresh cut-cos lettuce during Australian industrial practices was assessed. A probabilistic risk assessment model was developed and implemented in the @Risk software by using the Monte Carlo simulation technique with 1,000,000 iterations. Australian preharvest practices yielded predicted annual mean E. coli O157:H7 levels from 0.2 to -3.4 log CFU/g and prevalence values ranged from 2 to 6.4%. While exclusion of solar radiation from the baseline model yielded a significant increase in concentration of E. coli O157:H7 (-5.2 -log fold), drip irrigation usage, exclusion of manure amended soil and rainfall reduced E. coli O157:H7 levels by 7.4, 6.5, and 4.3-log fold, respectively. The microbial quality of irrigation water and irrigation type both had a significant effect on E. coli O157:H7 concentrations at harvest (p < 0.05). The probability of illness due to consumption of E. coli O157:H7 contaminated fresh cut-cos lettuce when water washing interventions were introduced into the processing module, was reduced by 1.4-2.7-log fold (p < 0.05). This study provides a robust basis for assessment of risk associated with E. coli O157:H7 contamination on fresh cut-cos lettuce for industrial practices and will assist the leafy green industry and food safety authorities in Australia to identify potential risk management strategies.

Overview of the Potential Impacts of Climate Change on the Microbial Safety of the Dairy Industry

Climate change is expected to affect many different sectors across the food supply chain. The current review paper presents an overview of the effects of climate change on the microbial safety of the dairy supply chain and suggest potential mitigation strategies to limit the impact. Raw milk, the common raw material of dairy products, is vulnerable to climate change, influenced by changes in average temperature and amount of precipitation. This would induce changes in the microbial profile and heat stress in lactating cows, increasing susceptibility to microbial infection and higher levels of microbial contamination. Moreover, climate change affects the entire dairy supply chain and necessitates adaptation of all the current food safety management programs. In particular, the review of current prerequisite programs might be needed as well as revisiting the current microbial specifications of the receiving dairy products and the introduction of new pretreatments with stringent processing regimes. The effects on microbial changes during distribution and consumer handling also would need to be quantified through the use of predictive models. The development of Quantitative Microbial Risk Assessment (QMRA) models, considering the whole farm-to-fork chain to evaluate risk mitigation strategies, will be a key step to prioritize actions towards a climate change-resilient dairy industry.

Evaluation of public health risk for Escherichia coli O157:H7 in cilantro

This study sought to model the growth and die-off of Escherichia coli (E. coli) O157:H7 along the cilantro supply chain from farm-to-fork to investigate its risk to public health. Contributing factors included in the model were on farm contamination from irrigation water and soil, solar radiation, harvesting, and transportation and storage times and temperatures. The developed risk model estimated the microbiological risks associated with E. coli O157:H7 in cilantro and determined the parameters that had the most effect on the estimated number of illnesses per year so future mitigation strategies could be applied. Results showed a similar decrease in the E. coli O157:H7 (median values) concentrations along the supply chain for cilantro grown in both winter and summer weather conditions. With an estimated 0.1% prevalence of E. coli O157:H7 contamination for cilantro post-harvest used for illustration, the model predicted the probability of illness from consuming fresh cilantro as very low with fewer than two illnesses per every one billion servings of cilantro (1.6 × 10^-9; 95th percentile). Although rare, 3.7% and 1.6% of scenarios run in this model for summer and winter grown cilantro, respectively, result in over 10 cases per year in the United States. This is reflected in real life where illnesses from cilantro are seen rarely but outbreaks have occurred. Sensitivity analysis and scenario testing demonstrated that ensuring clean and high quality irrigation water and preventing temperature abuse during transportation from farm to retail, are key to reducing overall risk of illness.

Effect of Weather on the Die-Off of Escherichia coli and Attenuated Salmonella enterica Serovar Typhimurium on Preharvest Leafy Greens following Irrigation with Contaminated Water

The Food Safety Modernization Act (FSMA) includes a time-to-harvest interval following the application of noncompliant water to preharvest produce to allow for microbial die-off. However, additional scientific evidence is needed to support this rule. This study aimed to determine the impact of weather on the die-off rate of Escherichia coli and Salmonella on spinach and lettuce under field conditions. Standardized, replicated field trials were conducted in California, New York, and Spain over 2 years. Baby spinach and lettuce were grown and inoculated with an ∼104-CFU/ml cocktail of E. coli and attenuated Salmonella Leaf samples were collected at 7 time points (0 to 96 h) following inoculation; E. coli and Salmonella were enumerated. The associations of die-off with study design factors (location, produce type, and bacteria) and weather were assessed using log-linear and biphasic segmented log-linear regression. A segmented log-linear model best fit die-off on inoculated leaves in most cases, with a greater variation in the segment 1 die-off rate across trials (-0.46 [95% confidence interval {95% CI}, -0.52, -0.41] to -6.99 [95% CI, -7.38, -6.59] log10 die-off/day) than in the segment 2 die-off rate (0.28 [95% CI, -0.20, 0.77] to -1.00 [95% CI, -1.16, -0.85] log10 die-off/day). A lower relative humidity was associated with a faster segment 1 die-off and an earlier breakpoint (the time when segment 1 die-off rate switches to the segment 2 rate). Relative humidity was also found to be associated with whether die-off would comply with FSMA's specified die-off rate of -0.5 log10 die-off/day.IMPORTANCE The log-linear die-off rate proposed by FSMA is not always appropriate, as the die-off rates of foodborne bacterial pathogens and specified agricultural water quality indicator organisms appear to commonly follow a biphasic pattern with an initial rapid decline followed by a period of tailing. While we observed substantial variation in the net culturable population levels of Salmonella and E. coli at each time point, die-off rate and FSMA compliance (i.e., at least a 2 log10 die-off over 4 days) appear to be impacted by produce type, bacteria, and weather; die-off on lettuce tended to be faster than that on spinach, die-off of E. coli tended to be faster than that of attenuated Salmonella, and die-off tended to become faster as relative humidity decreased. Thus, the use of a single die-off rate for estimating time-to-harvest intervals across different weather conditions, produce types, and bacteria should be revised.

On-farm wastewater treatment using biochar from local agroresidues reduces pathogens from irrigation water for safer food production in developing countries

In this study, the suitability of an anaerobic biofilter (AnBF) as an efficient and low-cost wastewater treatment for safer irrigation water production for Sub-Saharan Africa was investigated. To determine the influence of different ubiquitous available materials on the treatment efficiency of the AnBF, rice husks and their pyrolysed equivalent, rice husk biochar, were used as filtration media and compared with sand as a common reference material. Raw sewage from a municipal full-scale wastewater treatment plant pretreated with an anaerobic filter (AF) was used in this experiment. The filters were operated at 22 °C room temperature with a hydraulic loading rate of 0.05 m·h^-1 for 400 days. The mean organic loading rate (OLR) of the AF was 194 ± 74 and 63 ± 16 g_COD·m^-3·d^-1 for the AnBF. Fecal indicator bacteria (FIB) (up to 3.9 log₁₀-units), bacteriophages (up to 2.7 log₁₀-units), chemical oxygen demand (COD) (up to 94%) and turbidity (up to 97%) could be significantly reduced. Additionally, the essential plant nutrients nitrogen and phosphorous were not significantly affected by the water treatment. Overall, the performance of the biochar filters was significantly better than or equal to the sand and rice husk filters. By using the treated wastewater for irrigating lettuce plants in a pot experiment, the contamination with FIB was >2.5 log-units lower (for most of the plants below the detection limit of 5.6 MPN per gram fresh weight) than for plants irrigated with raw wastewater. Respective soil samples were minimally contaminated and nearly in the same range as that of tap water.

Survival and internalization of Salmonella and Escherichia coli O157:H7 sprayed onto different cabbage cultivars during cultivation in growth chambers

BACKGROUND

Cabbage may become contaminated with enteric pathogens during cultivation. Using multiple cabbage cultivars at two maturity stages (small plants or plants with small heads) in growth chamber studies, the fate (internalization or surface survival) of Salmonella and Escherichia coli O157:H7 (0157) were examined in conjunction with any potential relationships to the plant's antimicrobial content.

RESULTS

Internalized Salmonella was detected in cabbage within 24 h with prevalence ranging from 62% (16 of 26) for the 'Super Red 80' cultivar to 92% (24 of 26) for the 'Red Dynasty' cultivar. Surface survival of pathogens on small cabbage plants over nine days was significantly affected by cultivar with both pathogens surviving the most on the 'Farao' cultivar and Salmonella and O157 surviving the least on the 'Super Red 80' and 'Capture' cultivars, respectively (P < 0.05). Survival of O157 was slightly higher on cabbage heads for O157 than small plants suggesting that the maturity stage may affect this pathogen's fate. An inverse relationship existed between antimicrobial levels and the pathogen's surface survival on cabbage heads (P < 0.05).

CONCLUSIONS

The fate of pathogens varied with the cabbage cultivar in growth chamber studies highlighting the potential to explore cultivar in field studies to reduce the risk of microbiological contamination in this crop. © 2019 Society of Chemical Industry.

Season and Species: Two Possible Hurdles for Reducing the Food Safety Risk of Escherichia coli O157 Contamination of Leafy Vegetables

The food safety risk of Shiga toxin-producing Escherichia coli (STEC) infection per serving of leafy vegetables was investigated using a quantitative microbial risk assessment (QMRA) approach. The estimated level of E. coli O157 contamination was based on observed numbers of Enterobacteriaceae and E. coli on leafy vegetables grown and processed in southern Sweden from 2014 to 2016. Samples were collected before harvest, after washing, and at the end of shelf life. The observed counts were combined with data on the ratio of E. coli to E. coli O157 taken from earlier studies to estimate the probability of illness. The risks of STEC infection associated with species, either spinach ( Spinacia oleracea) or rocket ( Diplotaxis tenuifolia), growing season (spring or autumn), and washing (washed or not washed) were then evaluated. The results indicated that leafy vegetable species and growing season could be possible hurdles for reducing the food safety risk of STEC infection. At harvest, the probability of infection was 87% lower when consuming rocket compared with spinach and 90% lower when consuming leafy vegetables grown in spring compared with autumn. These relative risk reductions remained consistent even with other serving sizes and dose-response models. The lowest risk of STEC infection was associated with leafy vegetables early in the production chain, i.e., before harvest, while the risk increased during storage and processing. Consequently, the highest risk was observed when leafy vegetables were consumed at the end of shelf life. Washing had no effect on the food safety risk of STEC infection in this study. To improve the quality of QMRA, there is a need for additional data on the relationship between indicator organisms that can be easily enumerated (e.g., E. coli and Enterobacteriaceae) and E. coli strains that can cause STEC infection (e.g., E. coli O157) but are difficult to identify in food samples such as leafy vegetables.

Human exposure to antibiotic resistant-Escherichia coli through irrigated lettuce

Antibiotic resistant bacteria (ARB) have been found on fresh fruit and vegetables globally. These types of ARB infections are spreading rapidly and are a major human health threat. A quantitative human exposure assessment model was created using scenario analysis to investigate the potential human exposure to antibiotic resistant Escherichia coli (AR-E. coli) through the consumption of lettuce irrigated with surface water. Scientific literature and site specific data were collected to model each process from farm to fork to calculate the concentration of AR-E. coli on the lettuce at the point of human consumption. The processes examined were the adhesion, colonisation and viability of bacteria on the lettuce; the effect of different post-harvest cleaning processes; the effect of consuming the lettuce before, on or after the expiry date; and the effect of the consumer washing the lettuce. The results show the mean human exposure levels ranged between 1.00 × 10-2 and 1.35 × 106 colony forming units (CFU) of AR-E. coli per 100 g of surface water irrigated lettuce for the different scenarios investigated. The mean probability of illness from consuming 100 g of lettuce contaminated with potential pathogenic antibiotic-sensitive E. coli was between 1.46 × 10-9 to 1.88 × 10-2. A back calculation revealed that in order for the EC No 1441/2007 regulation to be exceeded (≥1000 CFU/g of E. coli on lettuce at the manufacturing stage), the mean contamination levels required in the irrigation water would need to be 2.7, 3.1 or 4.8 log CFU/ml using the post-harvest treatments of washing with water, rapid cooling with water and washing with a chlorine solution respectively. The information generated from this model could help to set guidelines for producers on maximum permissible AR-E. coli contamination levels in irrigation water and provides recommendations on the best post-harvest treatment to use.

Enterobacteria associated with houseflies (Musca domestica) as an infection risk indicator in swine production farms

Houseflies (Musca domestica) spend part of their life development on animal or human manure. Manure is high in pathogenic microbes; thus, houseflies have been known as a mechanical vector for various important zoonotic diseases. Therefore, the present study showcases captured houseflies from intensive swine production regions (which are areas of high manure concentration) in Southern Brazil, and analyses their bodies' to the presence of Escherichia coli and Salmonella sp. and the sensitivity of these bacteria to various antibiotics. Additionally, Quantitative Microbiology Risk Assessment was performed simulating the contamination of lettuce by flies' bacteria and subsequent lettuce consumption by an adult human being. Houseflies were captured in swine buildings and farm houses from five farms. E. coli quantification values ranged from 10⁴ to 10⁶ CFU/20 flies, and all sampling sites had positive results from bacteria presence in the collected houseflies. On the other hand, Salmonella sp. presence was observed in only three farms, where the quantification ranged from 10² to 10⁵ CFU/20 flies. The bacteria showed to be resistant to at least two from the four tested antibiotics (ampicillin, Cefalotin, Ciprofloxacin and Norfloxacin) antibiotics used in human or veterinary medicine. Infection probability analyses showed risk of human infection by E.coli, indicating possible transmission of zoonotic pathogens through flies. In this context, it was possible to conclude that there is a need for flies control, especially in swine farms where zoonotic pathogens can be abundant, to minimize the health impact of the vectorization of enteric bacteria.

Guidance on the requirements for the development of microbiological criteria

The European Food Safety Authority asked the Panel on Biological Hazards (BIOHAZ) to deliver a scientific opinion providing: (i) a review of the approaches used by the BIOHAZ Panel to address requests from risk managers to suggest the establishment of microbiological criteria; (ii) guidance on the required scientific evidence, data and methods/tools necessary for considering the development of microbiological criteria for pathogenic microorganisms and indicator microorganisms; (iii) recommendations on methods/tools to design microbiological criteria and (iv) guidelines for the requirements and tasks of risk assessors, compared to risk managers, in relation to microbiological criteria. This document provides guidance on approaches when: (i) a quantitative microbial risk assessment (QMRA) is available, (ii) prevalence and concentration data are available, but not a QMRA model, and (iii) neither a QMRA nor prevalence and/or concentration data are available. The role of risk assessors should be focused on assessing the impact of different microbiological criteria on public health and on product compliance. It is the task of the risk managers to: (1) formulate unambiguous questions, preferably in consultation with risk assessors, (2) decide on the establishment of a microbiological criterion, or target in primary production sectors, and to formulate the specific intended purpose for using such criteria, (3) consider the uncertainties in impact assessments on public health and on product compliance and (4) decide the point in the food chain where the microbiological criteria are intended to be applied and decide on the actions which should be taken in case of non‐compliance. It is the task of the risk assessors to support risk managers to ensure that questions are formulated in a way that a precise answer can be given, if sufficient information is available, and to ensure clear and unambiguous answers, including the assessment of uncertainties, based on available scientific evidence.

Quantitative contamination assessment of Escherichia coli in baby spinach primary production in Spain: Effects of weather conditions and agricultural practices

A quantitative microbial contamination model of Escherichia coli during primary production of baby spinach was developed. The model included only systematic contamination routes (e.g. soil and irrigation water) and it was used to evaluate the potential impact of weather conditions, agricultural practices as well as bacterial fitness in soil on the E. coli levels present in the crop at harvest. The model can be used to estimate E. coli contamination of baby spinach via irrigation water, via soil splashing due to irrigation water or rain events, and also including the inactivation of E. coli on plants due to solar radiation during a variable time of culturing before harvest. Seasonality, solar radiation and rainfall were predicted to have an important impact on the E. coli contamination. Winter conditions increased E. coli prevalence and levels when compared to spring conditions. As regards agricultural practices, both water quality and irrigation system slightly influenced E. coli levels on baby spinach. The good microbiological quality of the irrigation water (average E. coli counts in positive water samples below 1 log/100mL) could have influenced the differences observed among the tested agricultural practices (water treatment and irrigation system). This quantitative microbial contamination model represents a preliminary framework that assesses the potential impact of different factors and intervention strategies affecting E. coli concentrations at field level. Taking into account that E. coli strains may serve as a surrogate organism for enteric bacterial pathogens, obtained results on E. coli levels on baby spinach may be indicative of the potential behaviour of these pathogens under defined conditions.

Quantitative Microbial Risk Assessment for Escherichia coli O157:H7 in Fresh-Cut Lettuce

Leafy green vegetables, including lettuce, are recognized as potential vehicles for foodborne pathogens such as Escherichia coli O157:H7. Fresh-cut lettuce is potentially at high risk of causing foodborne illnesses, as it is generally consumed without cooking. Quantitative microbial risk assessments (QMRAs) are gaining more attention as an effective tool to assess and control potential risks associated with foodborne pathogens. This study developed a QMRA model for E. coli O157:H7 in fresh-cut lettuce and evaluated the effects of different potential intervention strategies on the reduction of public health risks. The fresh-cut lettuce production and supply chain was modeled from field production, with both irrigation water and soil as initial contamination sources, to consumption at home. The baseline model (with no interventions) predicted a mean probability of 1 illness per 10 million servings and a mean of 2,160 illness cases per year in the United States. All intervention strategies evaluated (chlorine, ultrasound and organic acid, irradiation, bacteriophage, and consumer washing) significantly reduced the estimated mean number of illness cases when compared with the baseline model prediction (from 11.4- to 17.9-fold reduction). Sensitivity analyses indicated that retail and home storage temperature were the most important factors affecting the predicted number of illness cases. The developed QMRA model provided a framework for estimating risk associated with consumption of E. coli O157:H7-contaminated fresh-cut lettuce and can guide the evaluation and development of intervention strategies aimed at reducing such risk.

Agrifood systems and the microbial safety of fresh produce: Trade-offs in the wake of increased sustainability

Fresh produce has been a growing cause of food borne outbreaks world-wide prompting the need for safer production practices. Yet fresh produce agrifood systems are diverse and under constraints for more sustainability. We analyze how measures taken to guarantee safety interact with other objectives for sustainability, in light of the diversity of fresh produce agrifood systems. The review is based on the publications at the interface between fresh produce safety and sustainability, with sustainability defined by low environmental impacts, food and nutrition security and healthy life. The paths for more sustainable fresh produce are diverse. They include an increased use of ecosystem services to e.g. favor predators of pests, or to reduce impact of floods, to reduce soil erosion, or to purify run-off waters. In contrast, they also include production systems isolated from the environment. From a socio-economical view, sustainability may imply maintaining small tenures with a higher risk of pathogen contamination. We analyzed the consequences for produce safety by focusing on risks of contamination by water, soil, environment and live stocks. Climate change may increase the constraints and recent knowledge on interactions between produce and human pathogens may bring new solutions. Existing technologies may suffice to resolve some conflicts between ensuring safety of fresh produce and moving towards more sustainability. However, socio-economic constraints of some agri-food systems may prevent their implementation. In addition, current strategies to preserve produce safety are not adapted to systems relying on ecological principles and knowledge is lacking to develop the new risk management approaches that would be needed.

Social structure and Escherichia coli sharing in a group-living wild primate, Verreaux's sifaka

Background

Epidemiological models often use information on host social contacts to predict the potential impact of infectious diseases on host populations and the efficiency of control measures. It can be difficult, however, to determine whether social contacts are actually meaningful predictors of transmission. We investigated the role of host social structure in the transmission of Escherichia coli in a wild population of primates, Verreaux’s sifakas (Propithecus verreauxi). Using multilocus sequence typing (MLST), we compared genetic similarities between E. coli isolates from different individuals and groups to infer transmission pathways.

Results

Correlation of social and transmission networks revealed that membership to the same group significantly predicted sharing of E. coli MLST sequence types (ST). Intergroup encounter rate and a measure of space-use sharing provided equally potent explanations for type sharing between social groups when closely related STs were taken into account, whereas animal age, sex and dispersal history had no influence. No antibiotic resistance was found, suggesting low rates of E. coli spillover from humans into this arboreal species.

Conclusions

We show that patterns of E. coli transmission reflect the social structure of this group-living lemur species. We discuss our results in the light of the species’ ecology and propose scent-marking, a type of social contact not considered in previous epidemiological studies, as a likely route of transmission between groups. However, further studies are needed to explicitly test this hypothesis and to further elucidate the relative roles of direct contact and environmental transmission in pathogen transfer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12898-016-0059-y) contains supplementary material, which is available to authorized users.

Assessing the Public Health Impact and Effectiveness of Interventions To Prevent Salmonella Contamination of Sprouts

Sprouts have been a recurring public health challenge due to microbiological contamination, and Salmonella has been the major cause of sprout-associated outbreaks. Although seed treatment and microbiological testing have been applied as risk reduction measures during sprout production, the extent to which their effectiveness in reducing the public health risks associated with sprouts has not been well investigated. We conducted a quantitative risk assessment to measure the risk posed by Salmonella contamination in sprouts and to determine whether and how mitigation strategies can achieve a satisfactory risk reduction based on the assumption that the risk reduction achieved by a microbiological sampling and testing program at a given sensitivity is equivalent to that achieved by direct inactivation of pathogens. Our results indicated that if the sprouts were produced without any risk interventions, the health impact caused by sprouts contaminated with Salmonella would be very high, with a median annual estimated loss of disability-adjusted life years (DALYs) of 691,412. Seed treatment (with 20,000 ppm of calcium hypochlorite) or microbiological sampling and testing of spent irrigation water (SIW) alone could reduce the median annual impact to 734 or 4,856 DALYs, respectively. Combining seed treatment with testing of the SIW would further decrease the risk to 58 DALYs. This number could be dramatically lowered to 3.99 DALYs if sprouts were produced under conditions that included treating seeds with 20,000 ppm of calcium hypochlorite plus microbiological testing of seeds, SIW, and finished products. Our analysis shows that the public health impact due to Salmonella contamination in sprouts could be controlled if seeds are treated to reduce pathogens and microbiological sampling and testing is implemented. Future advances in intervention strategies would be important to improve sprout safety further.

Using a Novel Wireless-Networked Decentralized Control Scheme under Unpredictable Environmental Conditions

The direction of sunshine or the installation sites of environmental control facilities in the greenhouse result in different temperature and humidity levels in the various zones of the greenhouse, and thus, the production quality of crop is inconsistent. This study proposed a wireless-networked decentralized fuzzy control scheme to regulate the environmental parameters of various culture zones within a greenhouse. The proposed scheme can create different environmental conditions for cultivating different crops in various zones and achieve diversification or standardization of crop production. A star-type wireless sensor network is utilized to communicate with each sensing node, actuator node, and control node in various zones within the greenhouse. The fuzzy rule-based inference system is used to regulate the environmental parameters for temperature and humidity based on real-time data of plant growth response provided by a growth stage selector. The growth stage selector defines the control ranges of temperature and humidity of the various culture zones according to the leaf area of the plant, the number of leaves, and the cumulative amount of light. The experimental results show that the proposed scheme is stable and robust and provides basis for future greenhouse applications.

Belgian and Spanish consumption data and consumer handling practices for fresh fruits and vegetables useful for further microbiological and chemical exposure assessment

A consumer survey was organized in Spain and Belgium to obtain consumption data and to gain insight into consumer handling practices for fresh vegetables consumed raw or minimally processed (i.e., heads of leafy greens, bell peppers, tomatoes, fresh herbs, and precut and packed leafy greens) and fruits to be consumed without peeling (i.e., apples, grapes, strawberries, raspberries, other berries, fresh juices, and precut mixed fruit). This information can be used for microbiological and/or chemical food safety research. After extensive cleanup of rough databases for missing and extreme values and age correction, information from 583 respondents from Spain and 1,605 respondents from Belgium (18 to 65 years of age) was retained. Daily intake (grams per day) was calculated taking into account frequency and seasonality of consumption, and distributions were obtained that can be used in quantitative risk assessment for chemical hazards with chronic effects on human health. Data also were recalculated to obtain discrete distributions of consumption per portion and the corresponding frequency of consumption, which can be used in acute microbiological risk assessment or outbreak investigations. The ranked median daily consumption of fruits and vegetables was similar in Spain and Belgium: apple > strawberry > grapes > strawberries and raspberries; and tomatoes > leafy greens > bell peppers > fresh herbs. However, vegetable consumption was higher (in terms of both portion and frequency of consumption) in Spain than in Belgium, whereas the opposite was found for fruit consumption. Regarding consumer handling practices related to storage time and method, Belgian consumers less frequently stored their fresh produce in a refrigerator and did so for shorter times compared with Spanish consumers. Washing practices for lettuce heads and packed leafy greens also were different. The survey revealed differences between these two countries in consumption and consumer handling practices, which can have an impact on outcomes of future microbiological or chemical risk assessment studies.

Agricultural and management practices and bacterial contamination in greenhouse versus open field lettuce production

The aim of this study was to gain insight into potential differences in risk factors for microbial contamination in greenhouse versus open field lettuce production. Information was collected on sources, testing, and monitoring and if applicable, treatment of irrigation and harvest rinsing water. These data were combined with results of analysis on the levels of Escherichia coli as a fecal indicator organism and the presence of enteric bacterial pathogens on both lettuce crops and environmental samples. Enterohemorragic Escherichia coli (EHEC) PCR signals (vt1 or vt2 positive and eae positive), Campylobacter spp., and Salmonella spp. isolates were more often obtained from irrigation water sampled from open field farms (21/45, 46.7%) versus from greenhouse production (9/75, 12.0%). The open field production was shown to be more prone to fecal contamination as the number of lettuce samples and irrigation water with elevated E. coli was significantly higher. Farmers comply with generic guidelines on good agricultural practices available at the national level, but monitoring of microbial quality, and if applicable appropriateness of water treatment, or water used for irrigation or at harvest is restricted. These results indicate the need for further elaboration of specific guidelines and control measures for leafy greens with regard to microbial hazards.

Fate and survival of Salmonella Typhimurium and Escherichia coli O157:H7 in repacked soil lysimeters after application of cattle slurry and human urine

BACKGROUND

Use of cattle slurry as a fertiliser is common practice around the world. Human urine use is not as common, but owing to its fertiliser value this might change in the future. It is essential to minimise the transfer of enteric pathogens through fertilisation, with respect to both animal and public health. Therefore the objective of this research was to study the survival and transport of Salmonella Typhimurium and Escherichia coli O157:H7 in two agricultural soils when applied to soil along with either cattle slurry or human urine over a period of 180 days.

RESULTS

Both Salmonella and E. coli O157:H7 were more rapidly reduced when applied together with human urine than when applied with cattle slurry. However, both pathogens persisted in low amounts at 20 and 50 cm depth in both soils throughout the whole study period. No Salmonella or E. coli O157:H7 was detected in the leachate over the 180 day study.

CONCLUSION

The risk of disease transmission is higher when cattle slurry is used as fertiliser compared with human urine. However, the risk of groundwater infiltration would be low as long as water velocity through the soil is moderate. Increased knowledge of pathogen persistence in soil after fertiliser application is a valuable tool for improving risk evaluations and formulating guidelines for the use of cattle and/or human wastes in cropping soils.

Evaluation of different approaches for modeling Escherichia coli O157:H7 survival on field lettuce

The ability to predict the behavior of Escherichia coli O157:H7 on contaminated field lettuce is essential for the development of accurate quantitative microbial risk assessments. The survival pattern of the species was assessed from several data sets derived from field-based experiments, which were analyzed by regression analysis fitting one monophasic model (log-linear) and two biphasic (Weibull and Cerf's model) models. Probabilistic models were also simulated with @RISK™, integrating the fitted monophasic and biphasic models in order to analyze their impact on the estimate of the extent of die-off subsequent to a contamination event in the field. Regression analysis indicated that E. coli O157:H7 followed a biphasic decay pattern in most cases, with the Weibull and Cerf's model showing similar good fit to individual and pooled survival data. Furthermore, results from the stochastic analysis demonstrated that using the log-linear model could lead to different risk estimates from those obtained with biphasic models, with a lower prevalence in the former scenario as no tailing is assumed in this model. The models and results derived from this work provide the first suitable mathematical base upon which to build probabilistic models to predict the fate of E. coli O157:H7 on field-grown leafy green vegetable.

Microbiological risk from minimally processed packaged salads in the Dutch food chain

The objective of this study was to evaluate the microbial hazard associated with the consumption of mixed salads produced under standard conditions. The presence of Salmonella, Campylobacter spp., and Escherichia coli O157 in the Dutch production chain of mixed salads was determined. Microbial prevalence and concentration data from a microbiological surveillance study were used as inputs for the quantitative microbial risk assessment. Chain logistics, production figures, and consumption patterns were combined with the survey data for the risk assessment chain approach. The results of the sample analysis were used to track events from contamination through human illness. Wide 95% confidence intervals around the mean were found for estimated annual numbers of illnesses resulting from the consumption of mixed salads contaminated with Salmonella Typhimurium DT104 (0 to 10,300 cases), Campylobacter spp. (0 to 92,000 cases), or E. coli (0 to 800 cases). The main sources of uncertainty are the lack of decontamination data (i.e., produce washing during processing) and an appropriate dose-response relationship.

Relationships among hygiene indicators and enteric pathogens in irrigation water, soil and lettuce and the impact of climatic conditions on contamination in the lettuce primary production

Eight Belgian lettuce farms located in the West Flanders were sampled to establish the relationships between levels of indicator bacteria, detection of enteric zoonotic pathogens and the temperature and precipitation during primary production. Pathogenic bacteria (PCR EHEC positives, Salmonella spp. or Campylobacter spp.) and indicator bacteria (total psychrotrophic aerobic plate count (TPAC), total coliforms, Escherichia coli, enterococci) were determined over a period of one and a half year from seedling leaves, peat-soil of the seedling, lettuce crops, field soil and irrigation water. Neither Salmonella isolates nor PCR EHEC signals were detected from lettuce although one out of 92 field soil samples contained Salmonella spp. and five soil samples provided PCR positives for EHEC virulence factors (vt1 or vt2 and eae gene). A low prevalence of Campylobacter (8/88) was noted in lettuce. It was shown that irrigation water is a major risk factor with regard to the bacterial contamination of the fresh produce as the water samples showed on a regular basis E. coli presence (59.2% of samples≥1CFU/100ml) and occasionally detection of pathogens (25%, n=30/120), in particular Campylobacter spp. The highest correlations between indicator bacteria, pathogens, temperature and the amount of precipitation were observed for the water samples in contrast to the soil or lettuce samples where no correlations were observed. The high correlations between E. coli, total coliforms and enterococci in the water implicated redundancy between analyses. Presence of elevated levels of E. coli increased the probability for the presence of pathogens (Campylobacter spp., EHEC and Salmonella spp.), but had a low to moderate predictive value on the actual presence of pathogens. The presence of pathogens and indicator bacteria in the water samples showed a seasonal effect as they tend to be more present during the months with higher temperature.