The Use of Direct‐Fed Microbials to Reduce Shedding of Escherichia coli O157 in Beef Cattle: A Systematic Review and Meta‐analysis

Human illness due to infections with Escherichia coli O157 is a serious health concern. Infection occurs through direct contact with infected animals or their faeces, through contaminated food or water and/or through person‐to‐person transmission. A reduction in faecal E. coli O157 shedding in cattle might reduce the burden of human infections. We used systematic review and meta‐analysis to assess the efficacy of direct‐fed microbials (DFM), compared with placebo or no treatment, fed during the pre‐harvest stage of production in reducing faecal E. coli O157 shedding in beef cattle during field trials. Four electronic databases, Nebraska Beef Reports and review article reference lists were searched. A total of 16 publications assessing faecal shedding at the end of the trial and/or throughout the trial period were included. The majority of publicly disseminated trials evaluated the prevalence of E. coli O157 faecal shedding; only two evaluated the concentration of organisms in faeces. The prevalence of faecal E. coli O157 shedding in cattle is significantly reduced by DFM treatments (summary effect size for all DFM – OR = 0.46; CI = 0.36–0.60). The DFM combination Lactobacillus acidophilus (NP51) and Propionibacterium freudenreichii (NP24) was more efficacious in reducing the prevalence of faecal E. coli O157 shedding at the time of harvest and throughout the trial period compared with the group of other DFM, although this difference was not statistically significant. Furthermore, we found that the combination [NP51 and NP24] treatment was more efficacious in reducing the prevalence of faecal E. coli O157 shedding at the time of harvest and throughout the trial period when fed at the dose of 10⁹ CFU/animal/day than any lesser amount, although this difference was not statistically significant. Feeding beef cattle DFM during the pre‐harvest stage of production reduces the prevalence of E. coli O157 faecal shedding and might effectively reduce human infections.     

A Multi‐Level Approach for Investigating Socio‐Economic and Agricultural Risk Factors Associated with Rates of Reported Cases of Escherichia coli O157 in Humans in Alberta,Canada

Using negative binomial and multi‐level Poisson models, the authors determined the statistical significance of agricultural and socio‐economic risk factors for rates of reported disease associated with Escherichia coli O157 in census subdivisions (CSDs) in Alberta, Canada, 2000–2002. Variables relating to population stability, aboriginal composition of the CSDs, and the economic relationship between CSDs and urban centres were significant risk factors. The percentage of individuals living in low‐income households was not a statistically significant risk factor for rates of disease. The statistical significance of cattle density, recorded at a higher geographical level, depended on the method used to correct for overdispersion, the number of levels included in the multi‐level models, and the choice of using all reported cases or only sporadic cases. Our results highlight the importance of local socio‐economic risk factors in determining rates of disease associated with E. coli O157, but their relationship with individual risk factors requires further evaluation.     

Severe Outbreak of Sorbitol‐Fermenting Escherichia coli O157 via Unpasteurized Milk and Farm Visits,Finland 2012

Shiga toxin‐producing, sorbitol‐fermenting Escherichia coli O157 (SF O157) has emerged as a cause of severe human illness. Despite frequent human findings, its transmission routes and reservoirs remain largely unknown. Foodborne transmission and reservoir in cattle have been suspected, but with limited supporting evidence. This study describes the outbreak of SF O157 that occurred in Finland in 2012. The outbreak originated from a recreational farm selling unpasteurized milk, as revealed by epidemiologic and microbiological investigations, and involved six hospitalized children and two asymptomatic adults with culture‐confirmed infection. An identical strain of SF O157 was isolated from patients, cattle and the farm environment, and epidemiologic analysis suggested unpasteurized milk as the vehicle of transmission. This study reports the first milkborne outbreak of SF O157, provides supporting evidence of cattle as a reservoir and highlights the health risks related to the consumption of unpasteurized milk.     

Assessing the Existing Information on the Efficacy of Bovine Vaccination against Escherichia coli O157:H7 – A Systematic Review and Meta‐analysis

The objective of this study was to conduct a systematic review and meta‐analysis to evaluate the existing information on the efficacy of commercial vaccination to reduce the prevalence of Escherichia coli O157:H7 in weaned cattle in beef feedlot finishing systems under commercial conditions. Currently, only two commercial vaccines exist, and thus, only publications reporting the use of vaccines targeting type III secreted proteins and/or siderophore receptor and porin proteins (SRP) were considered relevant. A total of 18 studies reporting 45 comparisons were included in this review. Meta‐analyses were conducted variously on (i) pre‐harvest outcomes, (ii) at‐harvest outcomes and (iii) both pre‐harvest and at‐harvest outcomes combined. Overall, efficacy of vaccination was consistently observed. Efficacy and homogeneity of the results was demonstrated for the two‐dose regimen, allowing us to conclude with confidence that the two‐dose approach is efficacious. For pre‐harvest outcomes and two‐dose regimens, the odds ratios (OR) were 0.53 (95% CI = 0.45–0.62) for the two vaccines combined and 0.49 (95% CI = 0.40–0.60) for vaccine targeting type III secreted proteins. The test for heterogeneity among studies yielded a Q test P = 0.354 for the two vaccines combined and Q test P = 0.269 for the vaccine targeting type III secreted proteins, indicating homogeneity in both cases. For pre‐ and at‐harvest outcomes combined and two‐dose regimens, the odds ratios (OR) were 0.52 (95% CI = 0.44–0.61) for the two vaccines combined and 0.45 (95% CI = 0.34–0.60) for vaccine targeting type III secreted proteins. The test for heterogeneity among studies yielded a Q test P = 0.134 for the two vaccines combined indicating homogeneity and Q test P = 0.089 for the vaccine targeting type III secreted proteins indicating heterogeneity. Based on this meta‐analysis, bovine vaccination appears to be an effective approach to the pre‐harvest control of E. coli O157:H7.