A systematic review and meta-analysis of the effectiveness of biosecurity and vaccination in reducing Salmonella spp. in broiler chickens

A Review on Microbiological Source Attribution Methods of Human Salmonellosis: From Subtyping to Whole-Genome Sequencing

Salmonella is one of the main causes of human foodborne illness. It is endemic worldwide, with different animals and animal-based food products as reservoirs and vehicles of infection. Identifying animal reservoirs and potential transmission pathways of Salmonella is essential for prevention and control. There are many approaches for source attribution, each using different statistical models and data streams. Some aim to identify the animal reservoir, while others aim to determine the point at which exposure occurred. With the advance of whole-genome sequencing (WGS) technologies, new source attribution models will greatly benefit from the discriminating power gained with WGS. This review discusses some key source attribution methods and their mathematical and statistical tools. We also highlight recent studies utilizing WGS for source attribution and discuss open questions and challenges in developing new WGS methods. We aim to provide a better understanding of the current state of these methodologies with application to Salmonella and other foodborne pathogens that are common sources of illness in the poultry and human sectors.

Vaccinating Meat Chickens against Campylobacter and Salmonella: A Systematic Review and Meta-Analysis

Foodborne enteritis is a major disease burden globally. Two of the most common causative bacterial enteropathogens in humans are Campylobacter and Salmonella species which are strongly associated with the consumption of raw or contaminated chicken. The poultry industry has approached this issue by use of a multi-hurdle method across the production chain to reduce or eliminate this risk. The use of poultry vaccines is one of these control methods. A systematic review and meta-analysis of vaccination effects against caecal Campylobacter and Salmonella were performed on primary research published between 2009 and 2022. Screening was conducted by three reviewers with one reviewer performing subsequent data extraction and one reviewer performing the risk of bias assessment. The confidence in cumulative evidence was evaluated based on the GRADE method. Meta-analyses were performed using standardised mean differences (SMDs) with additional analyses and random effects regression models on intervention effects grouped by the vaccine type. A total of 13 Campylobacter and 19 Salmonella studies satisfied the eligibility criteria for this review. Many studies included multi-arm interventions, resulting in a total of 25 Campylobacter and 34 Salmonella comparators which were synthesised. The analyses revealed a large reduction in pathogen levels; however, many effects required statistical adjustment due to unit of analysis errors. There was a moderate level of confidence in the reduction of Campylobacter by 0.93 SMD units (95% CI: −1.275 to −0.585; p value < 0.001) and a very low level of confidence in the reduction of Salmonella by 1.10 SMD units (95% CI: −1.419 to −0.776; p value < 0.001). The Chi2 test for heterogeneity (p value 0.001 and <0.001 for Campylobacter and Salmonella, respectively) and the I2 statistic (52.4% and 77.5% for Campylobacter and Salmonella, respectively) indicated high levels of heterogeneity in the SMDs across the comparators. The certainty of gathered evidence was also affected by a high risk of study bias mostly due to a lack of detailed reporting and, additionally for Salmonella, the presence of publication bias. Further research is recommended to source areas of heterogeneity, and a conscious effort to follow reporting guidelines and consider units of analysis can improve the strength of evidence gathered to provide recommendations to the industry.

Investigating the dynamics of Salmonella contamination in integrated poultry companies using a whole genome sequencing approach

The study of non-typhoid Salmonella in broiler integrations has been limited by the resolution of typing techniques. Although serotyping of Salmonella isolates is used as a traditional approach, it is not of enough resolution to clearly understand the dynamics of this pathogen within poultry companies. The aim of this research was to investigate the epidemiology and population dynamics of Salmonella serotypes in 2 poultry integrations using a whole genome sequencing approach. Two hundred and forty-three Salmonella isolates recovered from the broiler production chain of 2 integrated poultry companies were whole genome sequenced and analyzed with dedicated databases and bioinformatic software. The analyses of sequences revealed that S. Infantis was the most frequent serotype (82.3%). Most isolates showed a potential for resistance against medically important antibiotics and disinfectants. Furthermore, 97.5% of isolates harbored the pESI-like mega plasmid, that plays an important role in the global dissemination of AMR. SNP tree analysis showed that there were clones that are niche-specific while other ones were distributed throughout the broiler production chains. In this study, we demonstrated the potential of whole genome sequencing analysis for a comprehensive understanding of Salmonella distribution in integrated poultry companies. Data obtained with these techniques allow determination of the presence of genetic factors that play an important role in the environmental fitness and pathogenicity of Salmonella.

Assessment of the Effectiveness of Pre-harvest Meat Safety Interventions to Control Foodborne Pathogens in Broilers: a Systematic Review

Purpose of Review

Ensuring broilers’ meat safety is a priority to policy makers, producers, and consumers. This systematic review aims to update the recent knowledge on pre-harvest interventions to control main foodborne pathogens in broilers and to assess their effectiveness.

Recent Findings

A total of 815 studies were retrieved from PubMed® and Web of Science for 13 pathogens. In total, 51 studies regarding Campylobacter spp., Salmonella spp., VTEC, ESBL-AmpC Escherichia coli, and Clostridium perfringens were included in this review.

Summary

Research mostly focused on Salmonella spp. and Campylobacter spp. Biosecurity and management interventions had mixed outcomes, while the effectiveness of feed additives, though intensively researched, remains controversial. Research on other pathogens (i.e. ESBL-AmpC E. coli/Salmonella, and Toxoplasma gondii) was scarce, with publications focusing on epidemiology and/or on source-attribution studies. This is also true regarding research on Listeria monocytogenes, Bacillus cereus, Clostridium botulinum, Clostridium perfringens, and Staphylococcus aureus as these are frequently controlled by post-harvest interventions. Overall, studies on recent developments of novel pathogen-specific immunisation strategies are lacking.

Prevalence of Salmonella and Campylobacter spp. in Alternative and Conventionally Produced Chicken in the United States: A Systematic Review and Meta-Analysis

ABSTRACT

The burden of foodborne illness linked to the consumption of contaminated broiler meat is high in the United States. With the increase in popularity of alternative poultry rearing and production systems, it is important to identify the differences in food safety risks presented by alternative systems compared with conventional methods. Although many studies have been conducted that surveyed foodborne pathogen prevalence along the broiler supply chain, a systematic overview of all of the results is lacking. In the current study, a systematic review and meta-analysis were conducted to quantify the differences in prevalence of Salmonella and Campylobacter spp. in farm environment, rehang, prechill, postchill, and retail samples between conventional and alternative production systems. A systematic search of Web of Science and PubMed databases was conducted to identify eligible studies. Studies were then evaluated by inclusion criteria, and the included studies were qualitatively and quantitatively analyzed. In total, 137 trials from 72 studies were used in the final meta-analysis. Meta-analysis models were individually constructed for subgroups that were determined by sample type, pathogen, and production type. All subgroups possessed high amounts of heterogeneity (I2 > 75%). For environmental sample subgroups, Campylobacter prevalence was estimated to be 15.8 and 52.8% for conventional and alternative samples, respectively. Similar prevalence estimates for both production types were observed for Salmonella environmental samples and all retail samples. For conventional samples, Campylobacter and Salmonella prevalence was highest in prechill samples followed by rehang and postchill samples, respectively. The results herein will be useful in future quantitative microbial risk assessments for characterizing the differences in foodborne illness risks presented by different broiler production systems.

HIGHLIGHTS

A farm-to-fork quantitative risk assessment model for Salmonella Heidelberg resistant to third-generation cephalosporins in broiler chickens in Canada

Salmonella Heidelberg resistant to ceftiofur (a third-generation cephalosporin antimicrobial agent) in broiler chicken products pose a risk to public health in Canada. The objective of this study was to assess the extent of that risk and to evaluate the effect of intervention measures along the agri-food chain. A stochastic farm-to-fork quantitative microbial risk assessment model was developed following the Codex Alimentarius Guidelines for Risk Analysis of Foodborne Antimicrobial Resistance. Different scenarios were analyzed to assess the individual relative effects of 18 possible interventions in comparison to a baseline scenario. The baseline scenario represented the first year of on-farm antimicrobial use surveillance in the Canadian broiler industry and the year before an industry-imposed ban on the preventive use of antimicrobials of very high importance to human health (2013), where 31.3% of broiler flocks consisted of birds to which ceftiofur was administered. The baseline scenario predicted an average probability of illness of 1.1 per 100,000 servings (SE: 0.064 per 100,000), corresponding to an average of 22,000 human infections (SE: 1900) with ceftiofur-resistant S. Heidelberg per year, which is likely an overestimation. This risk was reduced by 90% or 20% when two separate scenarios designed to capture the effect of withdrawing preventive ceftiofur use from poultry production were simulated using different approaches; data used for the former scenario were confounded by other potential concomitant control measures (e.g. Salmonella vaccination programme), so the true effect likely lies somewhere between the two estimates. A theoretical 'worst case' scenario where all flocks had birds exposed to ceftiofur increased the risk by 107%. A 50% reduction in the probability of human prior exposure to antimicrobials, which has a selective and competitive effect for Salmonella spp. following ingestion of contaminated products, reduced the risk by 65%. Other promising measures that could be considered for further risk management included improved cleaning and disinfection between broiler flocks on farm (risk reduction by 26%), exclusive use of air chilling (risk reduction by 34%), and the improvement of meat storage and preparation conditions, e.g., no temperature abuse at retail (risk reduction by 88%). These findings showed the importance of a structured approach to assessing and potentially implementing effective interventions to reduce the risk associated with ceftiofur-resistant S. Heidelberg at different steps along the agri-food chain. Major data gaps included information on concentrations of resistant bacteria, cross contamination at processing and how ceftiofur-resistant S. Heidelberg behave in comparison with susceptible ones, e.g., in terms of growth and survival ability, as well as pathogenicity and virulence.

Bactericidal efficacy of potassium peroxymonosulfate under various concentrations, organic material conditions, exposure timing and its application on various surface carriers

Four concentrations of potassium peroxymonosulfate (PPMS) were evaluated for bactericidal activities and indicated that the concentration is less than the manufacturing-recommended concentrations, must extend the exposure time for bacterial inactivation. However, even with and without of organic material contamination, did not show marked inactivation difference. In addition, all concentrations were inactivated on all carrier surfaces within 30 sec, except on rubber where inactivation occurred within 1 min. However, quaternary ammonium compounds were inactivated on stainless steel and plastic within 1 min and 30 sec, respectively, but not inactivated within 5 min on rubber surfaces. Conclusion, PPMS inactivated bacteria under optimal concentration, organic material conditions, exposure timing and on carrier surfaces which can useful as an alternative disinfectant for biosecurity enhancement.

Application of slightly acidic electrolyzed water and ultraviolet light for Salmonella enteritidis decontamination of cell suspensions and surfaces of artificially inoculated plastic poultry transport coops and other facility surfaces

The efficiency of combination treatment of slightly acidic electrolyzed water (SAEW) and ultraviolet light (UV) for inactivation of Salmonella enteritidis (S. enteritidis) on the surface of plastic poultry coops and other facility surfaces was evaluated in the presence of organic matter. The bactericidal activities of SAEW, UV + SAEW, and composite phenol (CP) for inactivating S. enteritidis were also compared. Moreover, a model of UV + SAEW treatment of plastic transport coops with different times and available chlorine concentrations (ACC) was developed using multiple linear regression analysis. There are differences between SAEW and CP inactivation of S. enteritidis on coops, stainless steel, and glass surfaces (P < 0.05), and there are no differences between SAEW and CP on tire surfaces (P > 0.05). Disinfection of some rough material surfaces with SAEW treatment alone under feces interference on poultry farms may need a longer treatment time and/or a higher ACC than smooth surfaces. The combined treatment of UV and SAEW showed higher inactivation efficiency of S. enteritidis compared to CP and SAEW treatment alone (P < 0.05) in pure cultures or on the facility surfaces. A complete 100% inactivation of S. enteritidis on plastic poultry coop surfaces was obtained by using UV + SAEW with an ACC of 90 mg/L for more than 70 s. The established model had a good fit that was quantified by the determination coefficient R² (0.93) and a lack of fit test (P > 0.05). The bactericidal efficiency of UV + SAEW increased with greater ACC and increasing time. The findings of this study indicate that the combination treatment of UV and SAEW may be a promising disinfection method and could be used instead of SAEW alone, especially on rough materials in the presence of organic matter on poultry farms.

A within-flock model of Salmonella Heidelberg transmission in broiler chickens

As part of the development of a quantitative microbial risk assessment (QMRA) model of third-generation cephalosporins (3GC)-resistant Salmonella Heidelberg, a compartmental (SEIR) model for S. Heidelberg transmission within a typical Canadian commercial broiler chicken flock was developed. The model was constructed to estimate the within-flock prevalence and the bacterial concentration in the barn environment at pre-harvest, and to assess the effect of selected control measures. The baseline scenario predicted an average within-flock prevalence of 23.5 % (95 % tolerance interval: 15.7-31.4) and an average bacterial concentration of 3.579 (0-4.294) log CFU/g of feces in the barn environment at pre-harvest (on the day the flock is sent to slaughter). Because vertical introduction of S. Heidelberg into the barn was already uncommon in the baseline scenario, vaccination of broiler parent flocks appeared to have a negligible effect, while vaccination of broiler chicken flocks substantially reduced the bacterial concentration at pre-harvest. Cleaning and disinfection between batches markedly reduced the within-flock prevalence at pre-harvest, but the effect on bacterial concentration was limited outside of the beginning of the production period. Extending downtime between batches by 7 days had little effect on within-flock prevalence or bacterial concentration of S. Heidelberg when compared to the baseline scenario. This study provides a basis to describe S. Heidelberg dynamics within a broiler chicken flock and to predict the within-flock prevalence and bacterial concentration at pre-harvest, and includes a description of the limitations and data gaps. The results of these analyses and associated uncertainties are critical information for populating QMRA models of the downstream impacts on public health from on-farm and other food-chain practices. Specifically, the study findings will be integrated into a broader farm-to-fork QMRA model to support the risk-based control of S. Heidelberg resistant to 3GC in broiler chicken in Canada.

Potential for Meta-Analysis in the Realm of Preharvest Food Safety

Meta-analysis, the statistical combination of results from multiple studies, can be used to summarize all of the available research on an intervention, etiology, descriptive, or diagnostic test accuracy question. Meta-analysis should be conducted as a component of a systematic review, to increase transparency in the selection of studies and to incorporate an evaluation of the risk of bias in the individual studies included in the meta-analysis. The process of meta-analysis may include a forest plot to graphically display the study results and the calculation of a weighted average summary effect size. Heterogeneity (differences in the effect size between studies) can be evaluated using formal statistics and the reasons for heterogeneity can be explored using sub-group analysis or meta-regression. Thus, meta-analysis may be a useful methodology for preharvest food safety research to aid in policy or clinical decision-making or to provide input to quantitative risk assessment or other models.

Modeling disinfection of plastic poultry transport cages inoculated with Salmonella enteritids by slightly acidic electrolyzed water using response surface methodology

In order to reduce the risk of enteric pathogens transmission in animal farms, the disinfection effectiveness of slightly acidic electrolyzed water (SAEW, pH 5.85 to 6.53) for inactivating Salmonella Enteritidis on the surface of plastic poultry transport cages was evaluated. The coupled effects of the tap water cleaning time (5 to 15 s), SAEW treatment time (20 to 40 s), and available chlorine concentrations (ACCs) of 30 to 70 mg/l on the reductions of S. Enteritidis on chick cages were investigated using a central composite design of the response surface methodology (RSM). The established RS model had a goodness of fit quantified by the parameter R2 (0.971), as well as a lack of fit test (P>0.05). The maximum reduction of 3.12 log10 CFU/cm2 for S. Enteritidis was obtained for the cage treated with tap water cleaning for 15 s followed by SAEW treatment for 40 s at an ACC of 50 mg/l. Results indicate that the established RS model has shown the potential of SAEW in disinfection of bacteria on cages.

A guide for developing plain-language and contextual summaries of systematic reviews in agri-food public health

The application of systematic reviews is increasing in the agri-food public health sector to investigate the efficacy of policy-relevant interventions. In order to enhance the uptake and utility of these reviews for decision-making, there is a need to develop summary formats that are written in plain language and incorporate supporting contextual information. The objectives of this study were (1) to develop a guideline for summarizing systematic reviews in one- and three-page formats, and (2) to apply the guideline on two published systematic reviews that investigated the efficacy of vaccination and targeted feed and water additives to reduce Salmonella colonization in broiler chickens. Both summary formats highlight the key systematic review results and implications in plain language. Three-page summaries also incorporated four categories of contextual information (cost, availability, practicality, and other stakeholder considerations) to complement the systematic review findings. We collected contextual information through structured rapid reviews of the peer-reviewed and gray literature and by conducting interviews with 12 topic specialists. The overall utility of the literature searches and interviews depended on the specific intervention topic and contextual category. In general, interviews with topic specialists were the most useful and efficient method of gathering contextual information. Preliminary evaluation with five end-users indicated positive feedback on the summary formats. We estimate that one-page summaries could be developed by trained science-to-policy professionals in 3-5 days, while three-page summaries would require additional resources and time (e.g., 2-4 weeks). Therefore, one-page summaries are more suited for routine development, while three-page summaries could be developed for a more limited number of high-priority reviews. The summary guideline offers a structured and transparent approach to support the utilization of systematic reviews in decision-making in this sector. Future research is necessary to evaluate the utility of these summary formats for a variety of end-users in different contexts.