B.R. Berends

Microbial risks associated with exposure to pathogens in contaminated urban flood water.

Urban flood incidents induced by heavy rainfall in many cases entail flooding of combined sewer systems. These flood waters are likely to be contaminated and may pose potential health risks to citizens exposed to pathogens in these waters. The purpose of this study was to evaluate the microbial risk associated with sewer flooding incidents. Concentrations of Escherichia coli, intestinal enterococci and Campylobacter were measured in samples from 3 sewer flooding incidents. The results indicate faecal contamination: faecal indicator organism concentrations were similar to those found in crude sewage under high-flow conditions and Campylobacter was detected in all samples. Due to infrequent occurrence of such incidents only a small number of samples could be collected; additional data were collected from controlled flooding experiments and analyses of samples from combined sewers. The results were used for a screening-level quantitative microbial risk assessment (QMRA). Calculated annual risks values vary from 5 x 10(-6) for Cryptosporidium assuming a low exposure scenario to 0.03 for Giardia assuming a high exposure scenario. The results of this screening-level risk assessment justify further research and data collection to allow more reliable quantitative assessment of health risks related to contaminated urban flood waters.

Suggestions for the construction, analysis and use of descriptive epidemiological models for the modernization of meat inspection

There is consensus that scientifically validated, quantitative assessments of actual public health risks are a prerequisite for any sound modernization of current meat inspection procedures. This article outlines how such analyses could be conducted. Approaches that rely heavily upon extrapolations from theoretical dose-effect relationships are inadequate for the assessment of microbiological health risks associated with the production and consumption of meat. The use of highly structured and very elaborate descriptive epidemiological models covering the entire period from stable to table can be considered a promising solution. Health risks can be quantified by means of incidence rates and the influence of risk factors by means of odds ratios and (population) attributable fractions. A great advantage is that when it is not possible to quantify risks exactly, the descriptive models are detailed enough to be used in a hazard analysis critical control point (HACCP)-like approach and for writing validated codes of good manufacturing practice (GMP). There are, however, several conditions which have to be met before risk assessment can become the foundation of safety assurances for meat, such as active legislative support and the setting up of monitoring systems for zoonoses and other health hazards in animals and humans.

Risk factors of Coxiella burnetii (Q fever) seropositivity in veterinary medicine students.

Background Q fever is an occupational risk for veterinarians, however little is known about the risk for veterinary medicine students. This study aimed to assess the seroprevalence of Coxiella burnetii among veterinary medicine students and to identify associated risk factors. Methods A cross-sectional study with questionnaire and blood sample collection was performed among all veterinary medicine students studying in the Netherlands in 2006. Serum samples (n = 674), representative of all study years and study directions, were analyzed for C. burnetii IgG and IgM phase I and II antibodies with an immunofluorescence assay (IFA). Seropositivity was defined as IgG phase I and/or II titer of 1∶32 and above. Results Of the veterinary medicine students 126 (18.7%) had IgG antibodies against C. burnetii. Seropositivity associated risk factors identified were the study direction ‘farm animals’ (Odds Ratio (OR) 3.27 [95% CI 2.14–5.02]), advanced year of study (OR year 6: 2.31 [1.22–4.39] OR year 3–5 1.83 [1.07–3.10]) having had a zoonosis during the study (OR 1.74 [1.07–2.82]) and ever lived on a ruminant farm (OR 2.73 [1.59–4.67]). Stratified analysis revealed study direction ‘farm animals’ to be a study-related risk factor apart from ever living on a farm. In addition we identified a clear dose-response relation for the number of years lived on a farm with C. burnetii seropositivity. Conclusions C. burnetii seroprevalence is considerable among veterinary medicine students and study related risk factors were identified. This indicates Q fever as an occupational risk for veterinary medicine students.

Veterinary public health: Human health hazards associated with the administration of antimicrobials to slaughter animals

Summary This article describes the assessment of consumer risks of residues of tetracyclines in slaughter pigs in the Netherlands. The assessed risks were toxic and allergic reactions, and the disturbance of the consumers’ intestinal flora. Toxic and allergic reactions in humans and animals have only been observed at therapeutic doses, affecting between an estimated 1 in 5000 and one 1 in 140,000 individuals exposed. Residues of tetracyclines in pigs are closely associated with treatment with injectable formulations. Established Maximum Residue Levels (MRLs) do not reflect actual consumer risks in case a limit is violated incidentally. For example, when the established MRLs for tetracyclines in meat are exceeded with a factor 400, 40,000, and 200,000, respectively, the actual risk of an adverse drug reaction for the consumer following a single consumption of this meat is maximally 1 in 3 million, 1 in 300,000, and 1 in 8000, respectively. At the current estimated low levels of incidental exposure via pork, the annual risk of negative health effects for a random consumer is estimated at maximally 1 in 33 million. The annual risk that a temporary disturbance of the intestinal flora may also result in a facilitated infection with certain enteropathogens, such as Salmonella spp., is estimated at 1 in 45 million. It is concluded that the current microbiological risks of pork are greater than the risks of residues of tetracyclines as such, and that the control of the microbiological risks of pork should therefore be given first priority.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork.

Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.Summary Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2–5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0–150,000) become a carrier of resistant E. coli and/or resistance genes that originate from pigs, while an estimated 345,000 persons (175,000–600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food‐borne salmonellosis. Sometimes there are outbreaks of a specific multi‐resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vanco‐mycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self‐transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part I. An assessment of the risks of residues of tetracyclines in pork.

Summary This article describes the assessment of consumer risks of residues of tetracyclines in slaughter pigs in the Netherlands. The assessed risks were toxic and allergic reactions, and the disturbance of the consumers’ intestinal flora. Toxic and allergic reactions in humans and animals have only been observed at therapeutic doses, affecting between an estimated 1 in 5000 and one 1 in 140,000 individuals exposed. Residues of tetracyclines in pigs are closely associated with treatment with injectable formulations. Established Maximum Residue Levels (MRLs) do not reflect actual consumer risks in case a limit is violated incidentally. For example, when the established MRLs for tetracyclines in meat are exceeded with a factor 400, 40,000, and 200,000, respectively, the actual risk of an adverse drug reaction for the consumer following a single consumption of this meat is maximally 1 in 3 million, 1 in 300,000, and 1 in 8000, respectively. At the current estimated low levels of incidental exposure via pork, the annual risk of negative health effects for a random consumer is estimated at maximally 1 in 33 million. The annual risk that a temporary disturbance of the intestinal flora may also result in a facilitated infection with certain enteropathogens, such as Salmonella spp., is estimated at 1 in 45 million. It is concluded that the current microbiological risks of pork are greater than the risks of residues of tetracyclines as such, and that the control of the microbiological risks of pork should therefore be given first priority.

The price of the precautionary principle: Cost-effectiveness of BSE intervention strategies in the Netherlands

Since 1996, bovine spongiform encephalopathy (BSE) in cattle has been linked to a new variant of Creutzfeldt-Jakob disease (vCJD), a fatal brain disease in man. This paper assessed the cost-effectiveness of BSE control strategies instituted by the European Commission. In a Monte Carlo simulation model, a non-intervention baseline scenario was compared to three intervention strategies: removal of specified risk materials from slaughter animals, post-mortem testing for BSE and the culling of feed and age cohorts of BSE cases. The food risk in the baseline scenario ranged from 16.98 lost life years in 2002 to 2.69 lost life years in 2005. Removing specified risk materials removal practices, post-mortem testing and post-mortem testing plus cohort culling reduced this risk with 93%, 82.7% and 83.1%. The estimated cost-effectiveness of all BSE measures in The Netherlands ranged from 4.3 million euros per life year saved in 2002 to 17.7 million euros in 2005. It was discussed that the cost-effectiveness of BSE control strategies will further deviate from regular health economics thresholds as BSE prevalence and incidence declines.

Quantitative histological analysis of bovine small intestines before and after processing into natural sausage casings

A histological study was undertaken to determine the efficiency in the removal of the mucosa and Peyers patches by standard processing of bovine intestines into natural sausage casings. The second objective was to calculate the quantity of lymphoid and nervous tissue per consumable sausage. For the histological analysis, intestinal samples were collected from 80 beef cattle during the slaughter process. Fresh and cleaned intestines were compared in analyzing the thickness of the intestinal wall, weight reduction during cleaning, removal of the mucosal layer, and the presence of lymphoid and neural tissue after cleaning. The obtained data indicate a weight reduction of about 50% during standard cleaning procedures, as 90% of the mucosa and 48% of the lymphoid tissue are removed. Based on the quantitative histological image analysis, it was calculated that 1 m of cleaned casings, weighing on average 64 g, contains about 2.8 g of mucosa, 0.3 g of lymphoid tissue, and 0.1 g of neural tissue. Assuming, in a worst-case scenario, that the sausage casing is ingested when consuming 200 g of sausage at one meal, this consumption includes 0.09 g of lymphoid tissue and 0.02 g of neural tissue as part of the sausage casing. These data can be included in a risk assessment on the potentialexposure of consumers to bovine spongiform encephalopathy infectivity after eating sausages in beef casings.

Allergy among veterinary medicine students in The Netherlands

Background Veterinary medicine students who practice with animals are potentially exposed to many occupational agents, yet sensitisation and allergic symptoms among this group have not been studied extensively. Objective The objective of this study was to estimate the prevalence of sensitisation and allergic symptoms in veterinary medicine students in association with study specialisation over time. Methods A questionnaire-based cross-sectional study was conducted. Blood was collected and tested for total and specific serum IgE for 16 different common and study-specific allergens using enzyme immunoassay. Results New development of self-reported allergic symptoms to various allergens occurred in 8.7%, of which 44% was deducted against animals. Handling farm animals was strongly associated with self-reported allergies to various allergens (OR=6.9, 95% CI 1.9 to 25) and animal allergens (OR=12, 95% CI 1.4 to 103). Sensitisation to at least one allergen occurred in 33.1%. Sensitisation prevalence tended to be elevated in later years of the equine study program. In contrast to self-reported allergies, the prevalence of sensitisation to any allergen decreased with prolonged study duration for those specialising in farm animal health (years 3–5: OR=0.5, 95% CI 0.3 to 1.1; year 6: OR=0.2, 95% CI 0.1 to 0.5). This was independent of whether people were raised on a farm, which is in itself a protective factor for allergy and sensitisation. Conclusion This study provides evidence of an elevated prevalence of allergic symptoms with increasing years of veterinary study, suggesting that contact with animals, more specifically contact to farm animals, is a risk factor for the development of symptoms.