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 10(9) 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.

The evidentiary value of challenge trials for three pre-harvest food safety topics: a systematic assessment.

Reducing zoonotic pathogens in food animals prior to harvest will reduce the pathogen burden that enters the food chain and the environment. Consequently, the burden of enteric illness in humans may be reduced. Evaluating interventions to reduce a pathogen in animals often begins with challenge trials, in which animals are deliberately exposed to the pathogen under controlled conditions. Challenge trials are subsequently followed by field trials, also known as randomized controlled trials, in which the animals are naturally exposed to the pathogen. Challenge trials can most effectively inform field trials only if they precede field trials, are robust, internally valid and transparently reported. Using systematic review and meta-analysis methodology, we examined the pre-harvest food safety literature for three intervention-pathogen-species combinations: probiotics/competitive exclusion products in ruminants to reduce Escherichia coli O157 shedding, vaccines in ruminants to reduce E. coli O157 shedding and vaccines in swine to reduce Salmonella shedding. We examined two outcomes, prevalence of faecal shedding at the end of the trial and prevalence of faecal shedding throughout the trial period, to compare challenge trials and field trials. We found that challenge trials occurred concurrently with field trials, challenge trials suffered from reporting deficiencies of methodological features, challenge trials tended to report a more favourable outcome than field trials, and there was some evidence of publication bias among all three intervention-pathogen-species combinations. Challenge trials would better serve to inform field trials if they precede field trials, are methodologically sound, include transparent reporting and are published regardless of their results. In addition, due to our findings of greater efficacy reported among challenge trials compared with field trials, risk models predicting the public health benefits of pre-harvest interventions to reduce zoonotic pathogens in livestock might be best served by field trial results alone.

Spatial and temporal clustering of calcium oxalate and magnesium ammonium phosphate uroliths in dogs living in Ontario, Canada between 1998 and 2006.

Using the spatial scan statistic with a Bernoulli model, in a comparison of the two most common canine uroliths, calcium oxalate (CaOx) and magnesium ammonium phosphate (struvite) we determined whether there was evidence of spatial and/or temporal clustering of each urolith type based on canine submissions from Ontario to the Canadian Veterinary Urolith Centre (CVUC) between 1998 and 2006. During this period, there were 10,478 canine submissions, excluding cases that were identified as recurrent. We were able to georeference approximately 93% of these incident cases. After adjusting for spatial and temporal distributions of dogs based on the demographic risk factors of age, sex, and breed-type, statistically significant spatial and temporal clusters were present for both CaOx and struvite urolith types. A purely temporal struvite cluster occurred between February 10, 1998 and December 20, 2001, whereas, a purely temporal CaOx cluster occurred between September 2, 2005 and December 21, 2006. Hypotheses to explain the spatial clustering of uroliths include variation in the spatial distribution of water hardness, diet-type, access to veterinary care, and the use of surgical versus medical therapies to treat these uroliths. Based on the cluster locations, water hardness was unlikely to explain the spatial difference between the two cluster types whereas variables related to human population density were more consistent with our findings; the CaOx cluster occurred in the highest population density area of Ontario, and the struvite cluster occurred in the lowest population density area of southern Ontario. The temporal struvite cluster at the beginning and CaOx cluster at the end of the study period reflect a similar trend away from struvite towards CaOx urolithiasis among both canines and humans in the developed countries of North America and Europe.