Quantitative risk assessment of human infection from Escherichia coli O157 associated with recreational use of animal pasture

Animal and environmental risk factors for sporadic Shiga toxin-producing Escherichia coli (STEC) infection in England: a case control study for O157, O26 and other STEC serotypes

Most Shiga toxin-producing E. coli (STEC) infections are sporadic. Routine enhanced surveillance questionnaires of confirmed STEC cases in England contained promising data to conduct a case-control study to identify non-food exposures linked to the risk of becoming infected with different STEC serotypes, including O157, O26 and all others; this study pulled eligible cases from the recorded enhanced surveillance data. Controls were recruited from the general population and answered a comparable postal questionnaire. Logistic regression was performed to identify risk factors associated with STEC infection for O157, O26 and other serotype cases. In adjusted models, travel outside of the U.K. and childcare occupations raised the risk of infection for all serotypes. Day trips within the UK, exposure to dogs and contact with soil were linked to lower infection risk. Resident region within England was often linked to decreased risk. Summer season was linked to O157 and O26, but not other STEC. Swimming in the sea was linked to increased risk of infection by O157, but not other types of STEC. Correlations between exposures and infection were similar when the analysis was repeated excluding participants with a history of foreign travel. As the first case-control study in England to include sporadic non-O157 STEC, the varying risk factors between O157 and non-O157 cases suggest there are potentially unique reservoirs for different serotypes.

An agent-based model that simulates the spatio-temporal dynamics of sources and transfer mechanisms contributing faecal indicator organisms to streams. Part 2: Application to a small agricultural catchment

The new Model for the Agent-based simulation of Faecal Indicator Organisms (MAFIO) is applied to a small (0.42 km²) Scottish agricultural catchment to simulate the dynamics of E. coli arising from sheep and cattle farming, in order to provide a proof-of-concept. The hydrological environment for MAFIO was simulated by the "best" ensemble run of the tracer-aided ecohydrological model EcH₂O-iso, obtained through multi-criteria calibration to stream discharge (MAE: 1.37 L s^-1) and spatially-distributed stable isotope data (MAE: 1.14-3.02‰) for the period April-December 2017. MAFIO was then applied for the period June-August for which twice-weekly E. coli loads were quantified at up to three sites along the stream. Performance in simulating these data suggested the model has skill in capturing the transfer of faecal indicator organisms (FIOs) from livestock to streams via the processes of direct deposition, transport in overland flow and seepage from areas of degraded soil. Furthermore, its agent-based structure allowed source areas, transfer mechanisms and host animals contributing FIOs to the stream to be quantified. Such information is likely to have substantial value in the context of designing and spatially-targeting mitigation measures against impaired microbial water quality. This study also revealed, however, that avenues exist for improving process conceptualisation in MAFIO (e.g. to include FIO contributions from wildlife) and highlighted the need to quantitatively assess how uncertainty in the spatial extent of surface flow paths in the simulated hydrological environment may affect FIO simulations. Despite the consequent status of MAFIO as a research-level model, its encouraging performance in this proof-of-concept study suggests the model has significant potential for eventual incorporation into decision support frameworks.

Regional differences in presence of Shiga toxin-producing Escherichia coli virulence-associated genes in the environment in the North West and East Anglian regions of England

Shiga toxin-producing Escherichia coli is carried in the intestine of ruminant animals, and outbreaks have occurred after contact with ruminant animals or their environment. The presence of STEC virulence genes in the environment was investigated along recreational walking paths in the North West and East Anglia regions of England. In all, 720 boot sock samples from walkers' shoes were collected between April 2013 and July 2014. Multiplex PCR was used to detect E. coli based on the amplification of the uidA gene and investigate STEC-associated virulence genes eaeA, stx1 and stx2. The eaeA virulence gene was detected in 45·5% of the samples, where stx1 and/or stx2 was detected in 12·4% of samples. There was a difference between the two regions sampled, with the North West exhibiting a higher proportion of positive boot socks for stx compared to East Anglia. In univariate analysis, ground conditions, river flow and temperature were associated with positive boot socks. The detection of stx genes in the soil samples suggests that STEC is present in the English countryside and individuals may be at risk for infection after outdoor activities even if there is no direct contact with animals. SIGNIFICANCE AND IMPACT OF THE STUDY: Several outbreaks within the UK have highlighted the danger of contracting Shiga toxin-producing Escherichia coli from contact with areas recently vacated by livestock. This is more likely to occur for STEC infections compared to other zoonotic bacteria given the low infectious dose required. While studies have determined the prevalence of STEC within farms and petting zoos, determining the risk to individuals enjoying recreational outdoor activities that occur near where livestock may be present is less researched. This study describes the prevalence with which stx genes, indicative of STEC bacteria, were found in the environment in the English countryside.

Outbreaks of Shiga Toxin-Producing Escherichia coli Linked to Sprouted Seeds, Salad, and Leafy Greens: A Systematic Review

Shiga toxin-producing Escherichia coli (STEC) outbreaks involving ready-to-eat salad products have been described in the scientific literature since 1995. These products typically do not undergo a definitive control step such as cooking to eliminate pathogens. To reduce the number of STEC infections from salad products, efforts will need to focus on preventing and reducing contamination throughout the food chain. We performed a systematic review of STEC outbreaks involving sprouted seeds, salad, or leafy green products to determine whether there were recurrent features, such as availability of microbiological evidence or identification of the contamination event, which may inform future investigations and prevention and control strategies. Thirty-five STEC outbreaks linked to contaminated leafy greens were identified for inclusion. The outbreaks occurred from 1995 to 2018 and ranged from 8 to more than 8,500 cases. Detection of STEC in the food product was rare (4 of 35 outbreaks). For the remaining outbreaks, the determination of leafy greens as the source of the outbreak mainly relied on analytical epidemiology (20 of 35) or descriptive evidence (11 of 35). The traceback investigation in 21 of 32 outbreaks was not able to identify possible routes leading to where the STEC bacteria came from or how the leaves were contaminated. Investigations in eight outbreaks found poor practice during processing that may have contributed to the outbreak, such as insufficient postharvest disinfection of the product. Six outbreak investigations were able to identify the outbreak strain in animal feces near the growing fields; two of these were also able to find it in irrigation water on the farms, providing a likely route of contamination. These results highlight the limitations of relying on microbiological confirmation as a basis to initiate investigations of upstream production to understand the source of contamination. This review also demonstrates the importance of, and difficulties associated with, food-chain traceback studies to inform control measures and future prevention.

Toxigenic properties and stx phage characterization of Escherichia coli O157 isolated from animal sources in a developing country setting

Background

In many Asian countries including Bangladesh E. coli O157 are prevalent in animal reservoirs and in the food chain, but the incidence of human infection due to E. coli O157 is rare. One of the reasons could be inability of the organism from animal origin to produce sufficient amount of Shiga toxin (Stx), which is the main virulence factor associated with the severe sequelae of infection. This study aimed to fill out this knowledge gap by investigating the toxigenic properties and characteristics of stx phage of E. coli O157 isolated from animal sources in Bangladesh.

Results

We analysed 47 stx₂ positive E. coli O157 of food/animal origin for stx₂ gene variants, Shiga toxin production, presence of other virulence genes, stx phage insertion sites, presence of genes associated with functionality of stx phages (Q₉₃₃ and Q₂₁) and stx₂ upstream region. Of the 47 isolates, 46 were positive for both stx_2a and stx_2d while the remaining isolate was positive for stx_2d only. Reverse Passive Latex Agglutination assay (RPLA) showed that 42/47 isolates produced little or no toxin, while 5 isolates produced a high titre of toxin (64 to 128). 39/47 isolates were positive for the Toxin Non-Producing (TNP) specific regions in the stx₂ promoter. Additionally, all isolates were negative for antiterminator Q₉₃₃while a majority of isolates were positive for Q₂₁ gene suggesting the presence of defective stx phage. Of the yehV and wrbA phage insertion sites, yehV was found occupied in 11 isolates while wrbA site was intact in all the isolates. None of the isolates was positive for the virulence gene, cdt but all were positive for hlyA, katP, etpD and eae genes. Isolates that produced high titre Stx (n = 5) produced complete phage particles capable of infecting multiple bacterial hosts. One of these phages was shown to produce stable lysogens in host strains rendering the Stx2 producing ability.

Conclusion

Despite low frequency in the tested isolates, E. coli O157 isolates in Bangladesh carry inducible stx phages and have the capacity to produce Stx2, indicating a potential risk of E. coli O157 infection in humans.

Multi-Exposure Pathway Model to Compare Escherichia coli O157 Risks and Interventions

The relative contributions of exposure pathways associated with cattle-manure-borne Escherichia coli O157:H7 on public health have yet to be fully characterized. A stochastic, quantitative microbial risk assessment (QMRA) model was developed to describe a hypothetical cattle farm in order to compare the relative importance of five routes of exposure, including aquatic recreation downstream of the farm, consumption of contaminated ground beef processed with limited interventions, consumption of leafy greens, direct animal contact, and the recreational use of a cattle pasture. To accommodate diverse environmental and hydrological pathways, existing QMRAs were integrated with novel and simplistic climate and field-level submodels. The model indicated that direct animal contact presents the greatest risk of illness per exposure event during the high pathogen shedding period. However, when accounting for the frequency of exposure, using a high-risk exposure-receptor profile, consumption of ground beef was associated with the greatest risk of illness. Additionally, the model was used to evaluate the efficacy of hypothetical interventions affecting one or more exposure routes; concurrent evaluation of multiple routes allowed for the assessment of the combined effect of preharvest interventions across exposure pathways-which may have been previously underestimated-as well as the assessment of the effect of additional downstream interventions. This analysis represents a step towards a full evaluation of the risks associated with multiple exposure pathways; future incorporation of variability associated with environmental parameters and human behaviors would allow for a comprehensive assessment of the relative contribution of exposure pathways at the population level.

Assessing the risk of an emerging zoonosis of worldwide concern: anisakiasis

Anisakiasis is an emerging zoonosis caused by the fish parasitic nematode Anisakis. Spain appears to have the highest reported incidence in Europe and marinated anchovies are recognised as the main food vehicle. Using data on fishery landings, fish infection rates and consumption habits of the Spanish population from questionnaires, we developed a quantitative risk assessment (QRA) model for the anchovy value chain. Spaniards were estimated to consume on average 0.66 Anisakis per untreated (non-frozen) raw or marinated anchovy meal. A dose-response relationship was generated and the probability of anisakiasis was calculated to be 9.56 × 10-5 per meal, and the number of annual anisakiasis cases requiring medical attention was predicted between 7,700 and 8,320. Monte Carlo simulations estimated post-mortem migration of Anisakis from viscera to flesh increases the disease burden by >1000% whilst an education campaign to freeze anchovy before consumption may reduce cases by 80%. However, most of the questionnaire respondents who ate untreated meals knew how to prevent Anisakis infection. The QRA suggests that previously reported figures of 500 anisakiasis per year in Europe is a considerable underestimate. The QRA tool can be used by policy makers and informs industry, health professionals and consumers about this underdiagnosed zoonosis.

A quantitative microbiological risk assessment for Campylobacter in petting zoos

The significance of petting zoos for transmission of Campylobacter to humans and the effect of interventions were estimated. A stochastic QMRA model simulating a child or adult visiting a Dutch petting zoo was built. The model describes the transmission of Campylobacter in animal feces from the various animal species, fences, and the playground to ingestion by visitors through touching these so-called carriers and subsequently touching their lips. Extensive field and laboratory research was done to fulfill data needs. Fecal contamination on all carriers was measured by swabbing in 10 petting zoos, using Escherichia coli as an indicator. Carrier-hand and hand-lip touching frequencies were estimated by, in total, 13 days of observations of visitors by two observers at two petting zoos. The transmission from carrier to hand and from hand to lip by touching was measured using preapplied cow feces to which E. coli WG5 was added as an indicator. Via a Beta-Poisson dose-response function, the number of Campylobacter cases for the whole of the Netherlands (16 million population) in a year was estimated at 187 and 52 for children and adults, respectively, so 239 in total. This is significantly lower than previous QMRA results on chicken fillet and drinking water consumption. Scenarios of 90% reduction of the contamination (meant to mimic cleaning) of all fences and just goat fences reduces the number of cases by 82% and 75%, respectively. The model can easily be adapted for other fecally transmitted pathogens.

E. coli O157 outbreaks in the United Kingdom: past, present, and future

This review describes Escherichia coli O157 outbreaks in the United Kingdom, beginning from the first, in the 1980s, to those recorded in 2013. We point out that the United Kingdom differs from other countries, particularly the United States, in that it has had a considerable number of outbreaks associated with butchers, but very few caused by contaminated burgers. Two of the butcher-associated outbreaks (in central Scotland in 1996 and South Wales in 2005) were very large and are considered here in detail; the reviewer conducted detailed investigations into both outbreaks. Also considered is the very large outbreak that occurred in visitors to an open farm in Surrey in 2009. Detailed descriptions of some milk-borne outbreaks and incidents connected with camping and childrens' nurseries have been published, and these are also considered in this review. Large outbreaks in the United Kingdom have sometimes led to policy developments regarding food safety, and these are considered, together with public reactions to them, their health effect, and their value, as examples to follow or eschew in terms of the procedures to be adopted in response to incidents of this kind. Regulatory and legal consequences are also considered. As a wise man said, making predictions is difficult, particularly about the future. This review follows this position but points out that although human infections caused by E. coli O157 are rare in the United Kingdom, their incidence has not changed significantly in the last 17 years. This review points out that although a response to an outbreak is to say "lessons must be learned", this response has been tempered by forgetfulness. Accordingly, this review restricts its recommendations regarding outbreaks to two: the crucial importance of a rapid response and the importance of experience, and even "gut feeling", when an inspector is evaluating the safety of a food business.

An evaluation of microbial health risks to livestock fed with wastewater-irrigated forage crops

This paper presents the results of five experiments in which animal health risks associated with the consumption of crops irrigated with domestic wastewater were evaluated. Forage maize and Tanner grass were irrigated with treated wastewater and used in goats and calves feeding trials. The irrigated crops presented high levels of surface contamination with E. coli (10(4) -10(7) 25 g(-1) ) and salmonellae (up to 1.6 × 10(4) 25 g(-1)), but none of the animals showed signs of infection or of disease. Further, the microbiological quality of animal products always complied with the Brazilian and European Union standards for food safety. It is suggested that the WHO guideline values for restricted irrigation (≤ 10(4) E. coli 100 ml(-1) and ≤ 1 helminth egg l(-1)), which were developed to protect the health of agricultural field workers, would be equally protective of the health of both animals fed with wastewater-irrigated crops and humans consuming products from such animals.

Prevalence and concentration of Arcobacter spp. on Australian Beef Carcasses

The International Commission on Microbiological Specifications for Foods (ICMSF) classified Arcobacter spp. as emerging pathogens in 2002. Arcobacter spp. have been isolated from numerous food products at retail and from animal carcasses and feces at slaughter. A survey was conducted to determine both the prevalence and concentration of Arcobacter spp. on pre-chill beef carcasses. Surface swab samples were collected from 130 beef carcasses at the end of processing, prior to chilling. The concentration of Arcobacter spp. was determined by a most-probable-number per square centimeter (3 by 3) method with a limit of detection of 0.12 CFU/cm(2). Of the 100 carcasses examined from export abattoirs, 20 (20.0%) were contaminated with Arcobacter spp., and 5 of these had quantifiable levels of contamination ranging from 0.12 to 0.31 CFU/cm(2). Of the 30 carcasses examined at a pet food abattoir, 25 (83.3%) were contaminated with Arcobacter spp., and 10 of these had quantifiable levels of contamination ranging from 0.12 to 0.95 CFU/cm(2). Three species of Arcobacter, A. butzleri, A. cryaerophilus, and A. skirowii, were identified by PCR. Each of the species was present in an approximately equal ratio from export abattoirs. This study demonstrates that slaughter practices at export abattoirs are sufficient to maintain both low prevalence and low levels of contamination of beef carcasses with Arcobacter spp.

Combining risk assessment and epidemiological risk factors to elucidate the sources of humanE. coliO157 infection

E. coliO157 can be transmitted to humans by three primary (foodborne, environmental, waterborne) and one secondary (person-to-person transmission) pathways. A regression model and quantitative microbiological risk assessments (QMRAs) were applied to determine the relative importance of the primary transmission pathways in NE Scotland. Both approaches indicated that waterborne infection was the least important but it was unclear whether food or the environment was the main source of infection. The QMRAs over-predicted the number of cases by a factor of 30 and this could be because allE. coliO157 strains may not be equally infective and/or the level of infectivity in the dose–response model was too high. The efficacy of potential risk mitigation strategies to reduce human exposure toE. coliO157 using QMRAs was simulated. Risk mitigation strategies focusing on food and environment are likely to have the biggest impact on infection figures.

The relationship between lay and technical views of Escherichia coli O157 risk

Here, we bring together and contrast lay (accessible primarily through social science methodologies) and technical (via risk assessment and epidemiological techniques) views of the risk associated with the Escherichia coli O157 pathogen using two case study areas in the Grampian region of Scotland, and North Wales. Epidemiological risk factors of contact with farm animals, visiting farms or farm fields and having a private water supply were associated with postcode districts of higher than average disease incidence in the human population. However, this was not the case for the epidemiological risk factor of consumption of beef burgers, which was independent of disease incidence in the postcode district of residence. The proportion of the population expressing a high knowledge of E. coli O157 was greatest in high-incidence disease districts compared with low-incidence areas (17% cf. 7%). This supports the hypothesis that in high-disease-incidence areas, residents are regularly exposed to information about the disease through local cases, the media, local social networks, etc. or perhaps that individuals are more likely to be motivated to find out about it. However, no statistically significant difference was found between high- and low-incidence postcode districts in terms of the proportion of the population expressing a high likelihood of personal risk of infection (10% cf. 14%), giving a counterintuitive difference between the technical (epidemiological and quantitative microbiological risk assessment (QMRA)) and the lay assessment of E. coli O157 risk. This suggests that lay evaluations of E. coli O157 risk reflect intuitive and experience-based estimates of the risk rather than probabilistic estimates. A generally strong correspondence was found in terms of the rank order given to potential infection pathways, with environment and foodborne infection routes dominating when comparing public understanding with technical modelling results. Two general conclusions follow from the work. First, that integrative research incorporating both lay and technical views of risk is required in order that informed decisions can be made to handle or treat the risk by the groups concerned (e.g. the public, policy makers/risk managers, etc.). Second, when communicating risk, for example, through education programmes, it is important that this process is two-way with risk managers (e.g. including Food Standards Agency officials and communications team, public health infection control and environmental health officers) both sharing information with the public and stakeholder groups, as well as incorporating public knowledge, values and context (e.g. geographical location) into risk-management decisions.

Escherichia coli O157

Escherichia coli O157 is an uncommon but serious cause of gastroenteritis. This bacterium is noteworthy because a few, but significant, number of infected people develop the haemolytic uraemic syndrome, which is the most frequent cause of acute renal failure in children in the Americas and Europe. Many infections of E coli O157 could be prevented by the more effective application of evidence-based methods, which is especially important because once an infection has been established, no therapeutic interventions are available to lessen the risk of the development of the haemolytic uraemic syndrome. This Review takes into account the evolution and geographical distibution of E coli O157 (and its close pathogenic relatives); the many and varied routes of transmission from its major natural hosts, ruminant farm animals; and other aspects of its epidemiology, its virulence factors, the diagnosis and management of infection and their complications, the repercussions of infection including costs, and prevention.

Attribution of human VTEC O157 infection from meat products: a quantitative risk assessment approach

To address the risk posed to human health by the consumption of VTEC O157 within contaminated pork, lamb, and beef products within Great Britain, a quantitative risk assessment model has been developed. This model aims to simulate the prevalence and amount of VTEC O157 in different meat products at consumption within a single model framework by adapting previously developed models. The model is stochastic in nature, enabling both variability (natural variation between animals, carcasses, products) and uncertainty (lack of knowledge) about the input parameters to be modeled. Based on the model assumptions and data, it is concluded that the prevalence of VTEC O157 in meat products (joints and mince) at consumption is low (i.e., <0.04%). Beef products, particularly beef burgers, present the highest estimated risk with an estimated eight out of 100,000 servings on average resulting in human infection with VTEC O157.

Temporal and spatial patterns of bovine Escherichia coli O157 prevalence and comparison of temporal changes in the patterns of phage types associated with bovine shedding and human E. coli O157 cases in Scotland between 1998-2000 and 2002-2004

Background

Escherichia coli O157 is an important cause of acute diarrhoea, haemorrhagic colitis and, especially in children, haemolytic uraemic syndrome (HUS). Incidence rates for human E. coli O157 infection in Scotland are higher than most other United Kingdom, European and North American countries. Cattle are considered the main reservoir for E. coli O157. Significant associations between livestock related exposures and human infection have been identified in a number of studies.

Results

Animal Studies: There were no statistically significant differences (P = 0.831) in the mean farm-level prevalence between the two studies (SEERAD: 0.218 (95%CI: 0.141-0.32); IPRAVE: 0.205 (95%CI: 0.135-0.296)). However, the mean pat-level prevalence decreased from 0.089 (95%CI: 0.075-0.105) to 0.040 (95%CI: 0.028-0.053) between the SEERAD and IPRAVE studies respectively (P < 0.001). Highly significant (P < 0.001) reductions in mean pat-level prevalence were also observed in the spring, in the North East and Central Scotland, and in the shedding of phage type (PT) 21/28. Human Cases: Contrasting the same time periods, there was a decline in the overall comparative annual reported incidence of human cases as well as in all the major PT groups except 'Other' PTs. For both cattle and humans, the predominant phage type between 1998 and 2004 was PT21/28 comprising over 50% of the positive cattle isolates and reported human cases respectively. The proportion of PT32, however, was represented by few (<5%) of reported human cases despite comprising over 10% of cattle isolates. Across the two studies there were differences in the proportion of PTs 21/28, 32 and 'Other' PTs in both cattle isolates and reported human cases; however, only differences in the cattle isolates were statistically significant (P = 0.002).

Conclusion

There was no significant decrease in the mean farm-level prevalence of E. coli O157 between 1998 and 2004 in Scotland, despite significant declines in mean pat-level prevalence. Although there were declines in the number of human cases between the two study periods, there is no statistically significant evidence that the overall rate (per 100,000 population) of human E. coli O157 infections in Scotland over the last 10 years has altered. Comparable patterns in the distribution of PTs 21/28 and 32 between cattle and humans support a hypothesized link between the bovine reservoir and human infections. This emphasizes the need to apply and improve methods to reduce bovine shedding of E. coli O157 in Scotland where rates appear higher in both cattle and human populations, than in other countries.

Heterogeneous shedding of Brucella abortus in milk and its effect on the control of animal brucellosis

AIMS

To ascertain whether in Brucella abortus-infected water buffalo herds, the number of newly infected animals could be reduced by culling superspreaders (the animals secreting > or =10(4) CFU per ml of milk).

METHODS AND RESULTS

The number of B. abortus present in the milk (CFU per ml) from 500 water buffaloes was measured by the culture. Each animal was tested three times, at one month intervals. The presence or the absence of B. abortus in each milk sample was confirmed by PCR. A majority of infected animals shed the pathogen at a low level (< or =10(3) CFU ml(-1)). However, a few infected individuals (superspreaders) shed large numbers of B. abortus (> or =10(4) CFU ml(-1)). Quantitative PCR of B. abortus positive milk samples gave comparable results to culture. Culling of the superspreaders was sufficient to arrest the spread of infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

The approach described here can reduce significantly the cost of controlling brucellosis. Culture and quantitative PCR tests identify superspreaders and, compared with the serological tests in use to detect brucellosis, provide also a more accurate estimate of the disease incidence.

Factors associated with cross-contamination of hides of Scottish cattle by Escherichia coli O157

The putative source of hide contamination for 236 cattle in Scotland followed from the farm through to slaughter was determined using phage and verocytotoxin type data. The majority of cattle (84%) were found to have subtypes of Escherichia coli O157 on their hide that had not been found previously in any animal from the farm of origin, strongly suggesting that contamination occurred once animals had left the farm of origin. Using logistic regression analysis, several variables and factors were found to be strongly associated (P < 0.01) with cross-contamination of cattle hides at the univariate level; commercial transport to slaughter, transport with other animals, use of a crush, line automation, and increasing slaughterhouse throughput were all risk factors, while feeding hay in lairage, processing an animal earlier in a slaughter cohort, and cleaning the landing area poststunning were protective. In the multivariable model, with the slaughterhouse and the farm group included as random effects, factors associated with the cross-contamination of cattle hides were identified. Transport to the slaughterhouse by a commercial hauler had a borderline-significant association with increased odds of an animal having a cross-contaminated hide (odds ratio [OR] [95% confidence interval (CI)] = 5.7 [0.99, 33.0]; P = 0.05). At the slaughterhouse, providing hay to cattle waiting in lairage (OR [95% CI] = 0.04 [<0.01, 1.04]; P = 0.05) and cleaning the landing area (OR [95% CI] = 0.03 [<0.01, 1.15,]; P = 0.06) also had a borderline-significant association with decreased odds of an animal having a cross-contaminated hide. Although the prevalence of carcass contamination remains very low, targeted intervention at the preslaughter stage may have the potential to reduce further the risk to public health.

Extracting additional risk managers information from a risk assessment of Listeria monocytogenes in deli meats

The risk assessment study of Listeria monocytogenes in ready-to-eat foods conducted by the U.S. Food and Drug Administration is an example of an extensive quantitative microbiological risk assessment that could be used by risk analysts and other scientists to obtain information and by managers and stakeholders to make decisions on food safety management. The present study was conducted to investigate how detailed sensitivity analysis can be used by assessors to extract more information on risk factors and how results can be communicated to managers and stakeholders in an understandable way. The extended sensitivity analysis revealed that the extremes at the right side of the dose distribution (at consumption, 9 to 11.5 log CFU per serving) were responsible for most of the cases of listeriosis simulated. For concentration at retail, values below the detection limit of 0.04 CFU/g and the often used limit for L. monocytogenes of 100 CFU/g (also at retail) were associated with a high number of annual cases of listeriosis (about 29 and 82%, respectively). This association can be explained by growth of L. monocytogenes at both average and extreme values of temperature and time, indicating that a wide distribution can lead to high risk levels. Another finding is the importance of the maximal population density (i.e., the maximum concentration of L. monocytogenes assumed at a certain temperature) for accurately estimating the risk of infection by opportunistic pathogens such as L. monocytogenes. According to the obtained results, mainly concentrations corresponding to the highest maximal population densities caused risk in the simulation. However, sensitivity analysis applied to the uncertainty parameters revealed that prevalence at retail was the most important source of uncertainty in the model.

Escherichia coli O157: Burger bug or environmental pathogen?

The three main pathways of Escherichia coli O157 infection are foodborne, environmental (including direct contact with animals and their faeces and contaminated water supplies) or person to person contact. The disease is often nicknamed the 'burger bug' but it appears that environmental risk factors may be more important. In this study we use four techniques (outbreak analysis, case-control studies, disease mapping and quantitative microbial risk assessment (QMRA)) to determine whether burgers or environmental pathways present the greater risk in Scotland. Analysis of E. coli O157 outbreaks in Scotland from 1994 to 2003 associated with either meat or dairy foods, or with environmental transmission shows that approximately 40% [M1] of these outbreaks were foodborne, 54% were environmental and 6% involved both transmission routes. However, the largest outbreaks tend to be foodborne accounting for 83% of outbreak cases. Case-control studies indicate strong risk associations with environmental exposure in Scotland, the UK as a whole and the USA, but burgers appear to be more of a risk in the USA. Canadian, Scottish and Swedish disease mapping studies found positive association with indicators of cattle density. In Grampian (North-East Scotland) we found that there was a positive association with cattle and sheep density (divided by human population density) as well as percentage of population on private water supplies. We found 63% of cases in rural postcodes compared with 37% urban after correcting for population differences suggesting that at least 26% of cases may be classified as environmental. QMRA showed that on average, the risk was 100 times greater when visiting a pasture than eating a burger in Grampian. However, it is difficult to determine which pathway actually causes most illnesses as it is unknown how many burgers are consumed daily and what is the frequency of human visits to pasture. The implementation of hygienic food processing post-1996 Central Scotland outbreak and the preference for 'well done' burgers may account for this food being a relatively low risk thus making the 'burger bug' term less appropriate in the UK.

Vero-cytotoxigenic Escherichia coli O157 in pasteurized milk containers at the point of retail: a qualitative approach to exposure assessment

Dairies within the United Kingdom are classified into two groups, namely, off-farm and on-farm dairies (the latter often being small scale). We propose a model for the probability of milk sold as pasteurized reaching the point of retail contaminated with Vero-cytotoxigenic Escherichia coli (VTEC) O157 from each of these two pathways. We evaluate qualitatively the exposures inherent in each, and compare and contrast the two situations. The model framework is generic, in that it can in principle be used, with the relevant data modifications, to provide a qualitative assessment of the likely exposure from milk sold as pasteurized to any potentially milk-borne pathogenic organism. Furthermore, the methodological approaches presented are widely applicable in the microbial risk assessment field. The specific example presented will be of particular interest to the UK dairy and public health communities: we conclude that the exposure potential per liter consumed from milk processed in off-farm dairies is negligible, whereas the exposure potential per liter consumed from milk processed on-farm is low, but not sufficiently small to be regarded as negligible. We also identify areas of data sparsity, which need to be addressed for quantitative risk assessment to proceed, and highlight the critical points in the pasteurized milk production chain, which, in the event of a breakdown, have the potential to increase the risk to the consumer.

Confirmation of E. coli among other thermotolerant coliform bacteria in paper mill effluents, wood chips screening rejects and paper sludges

Paper sludges are solid wastes material generated from the paper production, which have been characterized for their chemical contents. Some are rich in wood fiber and are a good carbon source, for example the primary and de-inking paper sludges. Others are made rich in nitrogen and phosphorus by pressing the activated sludge, resulting from the biological water treatments, with the primary sludge, yielding the combined paper sludge. Still, in the absence of sanitary effluents very few studies have addressed the characterization of their coliform microflora. Therefore, this study investigated the thermotolerant coliform population of one paper mill effluent and two paper mill sludges and wood chips screening rejects using chromogenic media. For the first series of analyses, the medium used was Colilert broth and positive tubes were selected to isolate bacteria in pure culture on MacConkey agar. In a second series of analyses, double selective media, based on ss-galactosidase and ss-glucuronidase activities, were used to isolate bacteria. First, the presence of thermotolerant coliforms was detected in low numbers in most water effluents, but showed that the entrance of the thermotolerant coliforms was early in the industrial process. Also, large numbers of thermotolerant coliforms, i.e., 7,000,000 MPN/g sludge (dry weight; d.w.), were found in combined sludges. From this first series of isolations, bacteria were purified on MacConkey medium and identified as Citrobacter freundii, Enterobacter sp, E. sakazakii, E. cloacae, Escherichia coli, K. pneumoniae, K. pneumoniae subsp. rhinoscleromatis, K. pneumoniae subsp. ozaenae, K. pneumoniae subsp. pneumoniae, Pantoea sp, Raoultella terrigena, R. planticola. Second, the presence of thermotolerant coliforms was measured at more than 3,700-6,000 MPN/g (d.w) sludge, whereas E. coli was detected from 730 to more than 3,300 MPN/g (d.w.) sludge. The presence of thermotolerant coliform bacteria and E. coli was sometimes detected from wood chips screening rejects in large quantities. Also, indigenous E. coli were able to multiply into the combined sludge, and inoculated E. coli isolates were often able to multiply in wood chips and combined sludge media. In this second series of isolations, API20E and Biolog identified most isolates as E. coli, but others remained unidentified. The sequences of the 16S rDNA confirmed that most isolates were likely E. coli, few Burkholderia spp, but 10% of the isolates remained unidentified. This study points out that the coliform bacteria are introduced by the wood chips in the water effluents, where they can survive throught the primary clarifier and regrow in combined sludges.

Persistence of Escherichia coli O157 on farm surfaces under different environmental conditions

AIMS

To compare the persistence of Escherichia coli O157 on a variety of common faecally contaminated farmyard material surfaces (wood and steel) under different moisture and temperature regimes.

METHODS AND RESULTS

Samples of field-conditioned farmyard materials (galvanized steel and wood) were cut into pieces and contaminated with fresh cattle faeces inoculated with nontoxigenic E. coli O157 (strain 3704). Thereafter, they were stored at four different environmental conditions; with temperature (5 and 20 degrees C) and moisture (moist or dry) as variables. Transfer of the pathogen to hands from the surfaces was also evaluated. Escherichia coli O157 numbers declined over time on all surfaces albeit at different rates according to the sample material and environmental conditions. Persistence was greatest on moist wood samples under cooler temperatures with large population numbers remaining after 28 days. Desiccation of surfaces resulted in a more rapid decline in E. coli O157 populations under both temperature regimes. Substantial numbers of colonies may also potentially be transferred to human hands from the surfaces during brief contact.

CONCLUSIONS

When environmental conditions are favourable, E. coli O157 may persist for considerable times on a range of surfaces. However, when exposed to higher temperatures and dehydration, survival is notably decreased. Overall, bacterial persistence was significantly greater on wood samples relative to steel.

SIGNIFICANCE AND IMPACT OF THE STUDY

Escherichia coli O157 is a prevalent pathogen, common in ruminant faeces. Contact with contaminated faeces may lead to human infection, resulting in possible severe illness. Although our study used only one strain of bacteria, our findings indicates that E. coli O157 has the potential to persist for long periods of time on gates, stiles and other farmyard surfaces under a range of environmental conditions. These farmyard surfaces therefore pose a potential infection pathway particularly where there is a high risk of direct human contact (e.g. child petting zoos, open farms).

Spatial distribution of Escherichia coli O157-positive farms in Scotland

Using a sample of 949 Scottish farms with finishing cattle, the spatial distribution of Escherichia coli O157-positive farms was investigated using disease mapping models. The overall prevalence of E. coli O157-positive farms was estimated as 22%. The regions used in this study were the 16 postcode areas of Scotland. For each region, the posterior relative risk (RR) was estimated as a model-based alternative to the saturated standardized morbidity ratio (SMR), i.e., the ratio between observed and expected cases in a region. Three Bayesian hierarchical models with generalized linear modeling of the area-specific risks were used to estimate the posterior relative risk of E. coli O157-positive farms in the postcode areas: a random-effects model incorporating only spatially uncorrelated heterogeneity; a model incorporating both spatially correlated and uncorrelated heterogeneity; and a pseudo-mixture model with unstructured correlation and a weighted mix of two variance components representing the spatial correlation and a jump structure. None of the models identified any areas with a significant increase or decrease in risk. The deviance information criteria slightly favored the simplest model (RR range: 0.92--1.09). However, this model appeared to smooth out more of the variation in the RR compared to the pseudo-mixture model, which gave a more informative pattern of the posterior relative risks (range: 0.81--1.22).

Concentration and prevalence of Escherichia coli O157 in sheep faeces at pasture in Scotland

AIMS

To study the presence, numbers and virulence profiles of Escherichia coli O157 in sheep faeces and validate the microbiological methods used to attain these data.

METHODS AND RESULTS

Flock level prevalence was found to be 40% (six from 15) and 6.5% of faecal samples tested were found to be positive. Two farms gave samples defined as high shedding (>10(4) CFU g(-1)), one of which comprised 91% positive samples with 13/33 at the high shedding level.

CONCLUSIONS

These data confirmed that sheep are an important reservoir of E. coli O157.

SIGNIFICANCE AND IMPACT OF THE STUDY

Sheep play a significant role in the maintenance and dispersal of E. coli O157 in the farming environment and are an important source of human infection.

Transfer of Escherichia coli to water from drained and undrained grassland after grazing

The aim of this study was to determine the load of Escherichia coli transferred via drainage waters from drained and undrained pasture following a grazing period. Higher concentrations (ranging between 10(4) and 10(3) colony forming units [CFU] g(-1)) of E. coli persisted in soil for up to 60 d beyond the point where cattle were removed from the plots, but these eventually declined in the early months of spring to concentrations less than 10(2) CFU g(-1). The decline reflects the combined effect of cell depletion from the soil store through both wash-out and die-off of E. coli. No difference (P > 0.05) was observed in E. coli loads exported from drained and undrained plots. Similarly, no difference (P > 0.05) was observed in E. coli concentrations in drainage waters of mole drain flow and overland plus subsurface interflow. Intermittent periods of elevated discharge associated with storm events mobilized E. coli at higher concentrations (e.g., in excess of 400 CFU mL(-1)) than observed during low flow conditions (often <25 CFU mL(-1)). The combination of high discharge and cell concentrations resulted in the export of E. coli loads from drained and undrained plots exceeding 10(6) CFU L(-1) s(-1). The results highlight the potential for drained land to export E. coli loads comparable with those transferred from undrained pasture.

Concentration and prevalence of Escherichia coli O157 in cattle feces at slaughter

The concentration and prevalence of Escherichia coli O157 in cattle feces at the time of slaughter was studied over a 9-week period from May to July 2002. Fecal samples (n = 589) were collected from the rectums of slaughtered cattle, and the animal-level prevalence rate was estimated to be 7.5% (95% confidence interval [CI], 5.4 to 9.6%) while the group prevalence was 40.4% (95% CI, 27.7 to 53.2%). Of the 44 infected animals detected, 9% were high shedders that contained E. coli O157 at concentrations of >10(4) CFU g(-1). These 9% represented >96% of the total E. coli O157 produced by all animals tested. All isolates possessed the vt(2) gene, 39 had the eaeA gene, and a further five had the vt(1) gene also. The presence of high-shedding animals at the abattoir increases the potential risk of meat contamination during the slaughtering process and stresses the need for correctly implemented hazard analysis and critical control point procedures.