Eliciting expert opinion on the effectiveness and practicality of interventions in the farm and rural environment to reduce human exposure to Escherichia coli O157

Prioritization of pig farm biosecurity for control of Salmonella and hepatitis E virus infections: results of a European expert opinion elicitation

BACKGROUND

In the literature, there is absent or weak evidence on the effectiveness of biosecurity measures to the control of Salmonella spp. and hepatitis E virus (HEV) on pig farms. Therefore, the present study aimed to collect, weigh, and compare opinions from experts on the relevance of several biosecurity measures. An online questionnaire was submitted to selected experts, from multiple European countries, knowledgeable on either HEV or Salmonella spp., in either indoor or outdoor pig farming systems (settings). The experts ranked the relevance of eight biosecurity categories with regards to effectiveness in reducing the two pathogens separately, by assigning a score from a total of 80, and within each biosecurity category they scored the relevance of specific biosecurity measures (scale 1-5). Agreement among experts was analysed across pathogens and across settings.

RESULTS

After filtering for completeness and expertise, 46 responses were analysed, with 52% of the experts identified as researchers/scientists, whereas the remaining 48% consisted of non-researchers, veterinary practitioners and advisors, governmental staff, and consultant/industrial experts. The experts self-declared their level of knowledge but neither Multidimensional Scaling nor k-means cluster analyses produced evidence of an association between expertise and the biosecurity answers, and so all experts' responses were analysed together without weighting or adaptation. Overall, the top-ranked biosecurity categories were pig mixing; cleaning and disinfection; feed, water and bedding; and purchase of pigs or semen, while the lowest ranked categories were transport, equipment, animals (other than pigs and including wildlife) and humans. Cleaning and disinfection was ranked highest for both pathogens in the indoor setting, whereas pig mixing was highest for outdoor settings. Several (94/222, 42.3%) measures across all four settings were considered highly relevant. Measures with high disagreement between the respondents were uncommon (21/222, 9.6%), but more frequent for HEV compared to Salmonella spp.

CONCLUSIONS

The implementation of measures from multiple biosecurity categories was considered important to control Salmonella spp. and HEV on farms, and pig mixing activities, as well as cleaning and disinfection practices, were perceived as consistently more important than others. Similarities and differences in the prioritised biosecurity measures were identified between indoor and outdoor systems and pathogens. The study identified the need for further research especially for control of HEV and for biosecurity in outdoor farming.

Exploring expert opinion on the practicality and effectiveness of biosecurity measures on dairy farms in the United Kingdom using choice modeling

Biosecurity, defined as a series of measures aiming to stop disease-causing agents entering or leaving an area where farm animals are present, is very important for the continuing economic viability of the United Kingdom dairy sector, and for animal welfare. This study gathered expert opinion from farmers, veterinarians, consultants, academics, and government and industry representatives on the practicality and effectiveness of different biosecurity measures on dairy farms. The study used best-worst scaling, a technique that allows for greater discrimination between choices and avoids the variability in interpretation associated with other methods, such as Likert scales and ranking methods. Keeping a closed herd was rated as the most effective measure overall, and maintaining regular contact with the veterinarian was the most practical measure. Measures relating to knowledge, planning, and veterinary involvement; buying-in practices; and quarantine and treatment scored highly for effectiveness overall. Measures relating to visitors, equipment, pest control, and hygiene scored much lower for effectiveness. Overall, measures relating to direct animal-to-animal contact scored much higher for effectiveness than measures relating to indirect disease transmission. Some of the most effective measures were also rated as the least practical, such as keeping a closed herd and avoiding nose-to-nose contact between contiguous animals, suggesting that real barriers exist for farmers when implementing biosecurity measures on dairy farms. We observed heterogeneity in expert opinion on biosecurity measures; for example, veterinarians rated the effectiveness of consulting the veterinarian on biosecurity significantly more highly than dairy farmers, suggesting a greater need for veterinarians to promote their services on-farm. Still, both groups rated it as a practical measure, suggesting that the farmer-veterinarian relationship holds some advantages for the promotion of biosecurity.

Dairy farmers' use and non-use values in animal welfare: Determining the empirical content and structure with anchored best-worst scaling

In this study, we sought to identify empirically the types of use and non-use values that motivate dairy farmers in their work relating to animal welfare of dairy cows. We also sought to identify how they prioritize between these use and non-use values. Use values are derived from productivity considerations; non-use values are derived from the wellbeing of the animals, independent of the present or future use the farmer may make of the animal. In particular, we examined the empirical content and structure of the economic value dairy farmers associate with animal welfare of dairy cows. Based on a best-worst scaling approach and data from 123 Swedish dairy farmers, we suggest that the economic value those farmers associate with animal welfare of dairy cows covers aspects of both use and non-use type, with non-use values appearing more important. Using principal component factor analysis, we were able to check unidimensionality of the economic value construct. These findings are useful for understanding why dairy farmers may be interested in considering dairy cow welfare. Such understanding is essential for improving agricultural policy and advice aimed at encouraging dairy farmers to improve animal welfare; communicating to consumers the values under which dairy products are produced; and providing a basis for more realistic assumptions when developing economic models about dairy farmers' behavior.

Systematic review of expert elicitation methods as a tool for source attribution of enteric illness

Expert elicitation is a useful tool to explore sources of uncertainty and to answer questions where data are expensive or difficult to collect. It has been used across a variety of disciplines and represents an important method for estimating source attribution for enteric illness. A systematic review was undertaken to explore published expert elicitation studies, identify key considerations, and to make recommendations for designing an expert elicitation in the context of enteric illness source attribution. Fifty-nine studies were reviewed. Five key themes were identified: the expert panel including composition and recruitment; the pre-elicitation material, which clarifies the research question and provides training in uncertainty and probability; the choice of elicitation tool and method (e.g., questionnaires, surveys, and interviews); research design; and analysis of elicited data. Careful consideration of these themes is critical in designing and implementing an expert elicitation in order to reduce bias and produce the best possible results. While there are various epidemiological and microbiological methods available to explore source attribution of enteric illness, expert elicitation provides an opportunity to identify gaps in our understanding and where such studies are not feasible or available, represents the only possible method for synthesizing knowledge about transmission.

Stakeholder opinions on the practicality of management interventions to control bovine tuberculosis

Livestock disease control strategies are usually determined at national and international levels, yet their successful implementation is determined by stakeholders operating at local scales. Such stakeholders may also have detailed knowledge that would contribute to the development of disease control options suited to the socio-cultural and environmental conditions where management is undertaken. The aim of this study was to evaluate stakeholders' opinions of a list of potential bovine tuberculosis (TB) management interventions for South Central Spain. This area has high TB prevalence in wildlife and livestock, so veterinarians, livestock farmers and hunters are all key stakeholders in TB management. A literature review identified possible management activities. The effectiveness of each intervention was ranked by local experts, and practicality was ranked by hunters, cattle farmers and veterinarians, using a best-worst scaling exercise as part of a questionnaire. The most effective intervention, the banning of supplemental feeding of game species, was not considered practical by stakeholders. The most effective and practical interventions were the separation of wildlife and livestock access to waterholes, testing cattle every 3 months on farms with a recent positive TB case and removing gut-piles from the land after hunting events. Although all three of these options were well supported, each stakeholder group supported different approaches more strongly, suggesting that it might be effective to promote different disease management contributions in different stakeholder communities. This integrated approach contributes to the identification of the optimum combination of management tools that can be delivered effectively.

An analysis of cattle farmers' perceptions of drivers and barriers to on-farm control of Escherichia coli O157

Structural equation modelling and survey data were used to test determinants' influence on farmers' intentions towards Escherichia coli O157 on-farm control. Results suggest that farmers more likely to show willingness to spend money/time or vaccinate to control Escherichia coli O157 are those: who think farmers are most responsible for control; whose income depends more on opening farms to the public; with stronger disease control attitudes; affected by outbreaks; with better knowledge and more informed; with stronger perceptions of biosecurity measures’ practicality; using a health plan; who think farmers are the main beneficiaries of control; and whose farms are dairy rather than beef. The findings might suggest that farmers may implement on-farm controls for E. coli O157 if they identify a clear hazard and if there is greater knowledge of the safety and efficacy of the proposed controls.

Vaccination of Cattle against Escherichia coli O157:H7

Human infection with Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) is relatively rare, but the consequences can be serious, especially in the very young and the elderly. Efforts to control the flow of STEC O157 during beef processing have meaningfully reduced the incidence of human STEC O157 infection, particularly prior to 2005. Unfortunately, despite early progress, the incidence of STEC O157 infection has not changed meaningfully or statistically in recent years, suggesting that additional actions, for example, targeting the cattle reservoir, are necessary to further reduce STEC O157 illness. Ideally, preharvest interventions against STEC O157 should reduce the likelihood that cattle carry the organism, have practical application within the beef production system, and add sufficient value to the cattle to offset the cost of the intervention. A number of STEC O157 antigens are being investigated as potential vaccine targets. Some vaccine products have demonstrated efficacy to reduce the prevalence of cattle carrying STEC O157 by making the gut unfavorable to colonization. However, in conditions of natural exposure, efficacy afforded by vaccination depends on how the products are used to control environmental transmission within groups of cattle and throughout the production system. Although cattle vaccines against STEC O157 have gained either full or preliminary regulatory approval in Canada and the United States, widespread use by cattle feeders is unlikely until there is an economic signal to indicate that cattle vaccinated against STEC O157 are valued over other cattle.

Classification of Listeria monocytogenes persistence in retail delicatessen environments using expert elicitation and machine learning

Increasing evidence suggests that persistence of Listeria monocytogenes in food processing plants has been the underlying cause of a number of human listeriosis outbreaks. This study extracts criteria used by food safety experts in determining bacterial persistence in the environment, using retail delicatessen operations as a model. Using the Delphi method, we conducted an expert elicitation with 10 food safety experts from academia, industry, and government to classify L. monocytogenes persistence based on environmental sampling results collected over six months for 30 retail delicatessen stores. The results were modeled using variations of random forest, support vector machine, logistic regression, and linear regression; variable importance values of random forest and support vector machine models were consolidated to rank important variables in the experts' classifications. The duration of subtype isolation ranked most important across all expert categories. Sampling site category also ranked high in importance and validation errors doubled when this covariate was removed. Support vector machine and random forest models successfully classified the data with average validation errors of 3.1% and 2.2% (n = 144), respectively. Our findings indicate that (i) the frequency of isolations over time and sampling site information are critical factors for experts determining subtype persistence, (ii) food safety experts from different sectors may not use the same criteria in determining persistence, and (iii) machine learning models have potential for future use in environmental surveillance and risk management programs. Future work is necessary to validate the accuracy of expert and machine classification against biological measurement of L. monocytogenes persistence.

Subclinical infection and asymptomatic carriage of gastrointestinal zoonoses: occupational exposure, environmental pathways, and the anonymous spread of disease

Asymptomatic carriage of gastrointestinal zoonoses is more common in people whose profession involves them working directly with domesticated animals. Subclinical infections (defined as an infection in which symptoms are either asymptomatic or sufficiently mild to escape diagnosis) are important within a community as unknowing (asymptomatic) carriers of pathogens do not change their behaviour to prevent the spread of disease; therefore the public health significance of asymptomatic human excretion of zoonoses should not be underestimated. However, optimal strategies for managing diseases where asymptomatic carriage instigates further infection remain unresolved, and the impact on disease management is unclear. In this review we consider the environmental pathways associated with prolonged antigenic exposure and critically assess the significance of asymptomatic carriage in disease outbreaks. Although screening high-risk groups for occupationally acquired diseases would be logistically problematical, there may be an economic case for identifying and treating asymptomatic carriage if the costs of screening and treatment are less than the costs of identifying and treating those individuals infected by asymptomatic hosts.

Reducing the public health risk of Escherichia coli O157 exposure by immunization of cattle

The One Health approach investigates the complexities surrounding the interplay between the animal, human and environmental domains. Zoonotic pathogens, such as Escherichia coli (E. coli) O157, which have animal reservoirs, also have direct impact on public health. Cattle are the primary reservoir of E. coli O157, however infection with this bacterium is asymptomatic. Infected cattle appear healthy and have normal growth rates and milk production abilities. Each year, thousands of Canadians become ill following exposure to E. coli O157. To reduce this public health risk, immunization of cattle would be an effective intervention. Several models have shown that on-farm pathogen reduction programs would significantly reduce the risk of human illness.

Cost-effectiveness of farm interventions for reducing the prevalence of VTEC O157 on UK dairy farms

A randomized control trial on verocytotoxigenic Escherichia coli (VTEC)-infected farms found evidence that: (1) keeping animals in the same group; (2) maintaining dry bedding; (3) preventing direct contact with neighbouring cattle; and (4) maintaining a closed herd, were associated with a reduced risk of infection in youngstock aged 3–18 months. This study evaluated these interventions using a cost-effectiveness framework for UK dairy farms. Keeping animals in the same group was considered to have negligible cost and was feasible for herds containing over 77 dairy cows. Assuming equal efficacy of the remaining interventions, preventing direct contact between neighbouring cattle is most cost-effective with a median annual cost of £2.76 per cow. This compares to £4.18 for maintaining dry bedding and £17.42 for maintaining a closed herd using quarantine procedures. Further model validation and exploration of other potential benefits are required before making policy decisions on VTEC control.