Food-borne diseases - the challenges of 20 years ago still persist while new ones continue to emerge.

The burden of diseases caused by food-borne pathogens remains largely unknown. Importantly data indicating trends in food-borne infectious intestinal disease is limited to a few industrialised countries, and even fewer pathogens. It has been predicted that the importance of diarrhoeal disease, mainly due to contaminated food and water, as a cause of death will decline worldwide. Evidence for such a downward trend is limited. This prediction presumes that improvements in the production and retail of microbiologically safe food will be sustained in the developed world and, moreover, will be rolled out to those countries of the developing world increasingly producing food for a global market. In this review evidence is presented to indicate that the microbiological safety of food remains a dynamic situation heavily influenced by multiple factors along the food chain from farm to fork. Sustaining food safety standards will depend on constant vigilance maintained by monitoring and surveillance but, with the rising importance of other food-related issues, such as food security, obesity and climate change, competition for resources in the future to enable this may be fierce. In addition the pathogen populations relevant to food safety are not static. Food is an excellent vehicle by which many pathogens (bacteria, viruses/prions and parasites) can reach an appropriate colonisation site in a new host. Although food production practices change, the well-recognised food-borne pathogens, such as Salmonella spp. and Escherichia coli, seem able to evolve to exploit novel opportunities, for example fresh produce, and even generate new public health challenges, for example antimicrobial resistance. In addition, previously unknown food-borne pathogens, many of which are zoonotic, are constantly emerging. Current understanding of the trends in food-borne diseases for bacterial, viral and parasitic pathogens has been reviewed. The bacterial pathogens are exemplified by those well-recognized by policy makers; i.e. Salmonella, Campylobacter, E. coli and Listeria monocytogenes. Antimicrobial resistance in several bacterial food-borne pathogens (Salmonella, Campylobacter, Shigella and Vibrio spp., methicillin resistant Staphylcoccus aureas, E. coli and Enterococci) has been discussed as a separate topic because of its relative importance to policy issues. Awareness and surveillance of viral food-borne pathogens is generally poor but emphasis is placed on Norovirus, Hepatitis A, rotaviruses and newly emerging viruses such as SARS. Many food-borne parasitic pathogens are known (for example Ascaris, Cryptosporidia and Trichinella) but few of these are effectively monitored in foods, livestock and wildlife and their epidemiology through the food-chain is poorly understood. The lessons learned and future challenges in each topic are debated. It is clear that one overall challenge is the generation and maintenance of constructive dialogue and collaboration between public health, veterinary and food safety experts, bringing together multidisciplinary skills and multi-pathogen expertise. Such collaboration is essential to monitor changing trends in the well-recognised diseases and detect emerging pathogens. It will also be necessary understand the multiple interactions these pathogens have with their environments during transmission along the food chain in order to develop effective prevention and control strategies.

Human health consequences of use of antimicrobial agents in aquaculture.

Intensive use of antimicrobial agents in aquaculture provides a selective pressure creating reservoirs of drug-resistant bacteria and transferable resistance genes in fish pathogens and other bacteria in the aquatic environment. From these reservoirs, resistance genes may disseminate by horizontal gene transfer and reach human pathogens, or drug-resistant pathogens from the aquatic environment may reach humans directly. Horizontal gene transfer may occur in the aquaculture environment, in the food chain, or in the human intestinal tract. Among the antimicrobial agents commonly used in aquaculture, several are classified by the World Health Organisation as critically important for use in humans. Occurrence of resistance to these antimicrobial agents in human pathogens severely limits the therapeutic options in human infections. Considering the rapid growth and importance of aquaculture industry in many regions of the world and the widespread, intensive, and often unregulated use of antimicrobial agents in this area of animal production, efforts are needed to prevent development and spread of antimicrobial resistance in aquaculture to reduce the risk to human health.

Antimicrobial resistance in Staphylococcus pseudintermedius in the Norwegian dog population.

The occurrence of antimicrobial resistance in Staphylococcus pseudintermedius from skin and ear infections in a representative sample of dogs unexposed to antimicrobial treatment before sampling was examined. The obtained isolates were further examined for genetic polymorphism and genetic background of resistance. A total of 59 isolates of S. pseudintermedius originating from 96 samples of 91 dogs in five different regions in Norway were included in this study. Susceptibility testing was performed using a broth dilution method. Resistant isolates were subjected to polymerase chain reaction for detection of resistance genes. All isolates were subjected to pulsed-field gel electrophoresis to examine the genetic polymorphism. In total, 19% of the isolates were susceptible to all antimicrobial agents included. Resistance to penicillin was most prevalent (70%), followed by resistance to fusidic acid (49%) and oxytetracycline (42%). Resistance to quinolones or cephalosporins was not observed. Resistance to penicillin, tetracycline, and erythromycin was mediated by the blaZ beta-lactamase gene, the tetM gene, and the ermB gene, respectively. One of the fusidic acid-resistant isolates harbored a fusC gene, whereas the mechanisms involved in resistance in the other fusidic acid-resistant isolates remained unknown. Pulsed-field gel electrophoresis showed a high genetic polymorphism of S. pseudintermedius. This study indicates that the occurrence of antimicrobial resistance is common among S. pseudintermedius from dogs unexposed to antimicrobial treatment before sampling, and that there is a high genetic polymorphism among S. pseudintermedius.

Prescription of antimicrobial drugs in Norwegian aquaculture with an emphasis on "new" fish species.

The usage of antimicrobial (AM) drugs in farmed fish in Norwegian aquaculture for the period 2000-2005 was investigated by using prescription data. These data were validated against national sales data of AM drugs sold for use in farmed fish and were found to be highly valid. The defined course dose (DCD) was applied as the unit of measurement to correct for the variations in the dosages between different AM drugs. The DCD(kg) was the amount of an AM drug recommended for the treatment of a 1-kg fish. The calculated number of prescribed DCD(kg)s is an estimate of the biomass of farmed fish that can be treated with a certain amount AM drug. In the present study, the number of prescriptions issued (i.e., numbers of initiated treatments), weight of active substance prescribed and biomass treated were applied to describe the usage. An increase, although modest, in the AM drug usage in Norwegian aquaculture was observed from 2002 to 2005. This increase was accounted for by new-farmed fish species (other than Atlantic salmon and rainbow trout), especially Atlantic cod. The increased usage of AM drugs in cod in the study period was significantly positively correlated to the biomass produced; even so from 2001 to 2005 the number of prescriptions for cod relative to the produced biomass declined. The AM drug usage in Atlantic halibut as well as the production varied during the study period. For other species such as turbot, coalfish and wolffish the usage of AM drugs was found to be negligible. "Mono-therapy" with quinolones may present a selective pressure in regard to development of quinolone resistance.

Triclosan and antimicrobial resistance in bacteria: an overview.

Triclosan is a widely used biocide that is considered as an effective antimicrobial agent against different microorganisms. It is included in many contemporary consumer and personal health-care products, like oral and dermal products, but also in household items, including plastics and textiles. At bactericidal concentrations, triclosan appears to act upon multiple nonspecific targets, causing disruption of bacterial cell wall functions, while at sublethal concentrations, triclosan affects specific targets. During the 1990s, bacterial isolates with reduced susceptibility to triclosan were produced in laboratory experiments by repeated exposure to sublethal concentrations of the agent. Since 2000, a number of studies have verified the occurrence of triclosan resistance amongst dermal, intestinal, and environmental microorganisms, including some of clinical relevance. Of major concern is the possibility that triclosan resistance may contribute to reduced susceptibility to clinically important antimicrobials, due to either cross-resistance or co-resistance mechanisms. Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials.

Incidence trend and risk factors for campylobacter infections in humans in Norway.

BACKGROUND: The objectives of the study were to evaluate whether the increase in incidence of campylobacteriosis observed in humans in Norway from 1995 to 2001 was statistically significant and whether different biologically plausible risk factors were associated with the incidence of campylobacteriosis in the different counties in Norway. METHODS: To model the incidence of domestically acquired campylobacteriosis from 1995 to 2001, a population average random effect poisson model was applied (the trend model). To case data and assumed risk-factor/protective data such as sale of chicken, receiving treated drinking water, density of dogs and grazing animals, occupation of people in the municipalities and climatic factors from 2000 and 2001, an equivalent model accounting for geographical clustering was applied (the ecological model). RESULTS: The increase in incidence of campylobacteriosis in humans in Norway from 1995 to 2001 was statistically significant from 1998. Treated water was a protective factor against Campylobacter infections in humans with an IRR of 0.78 per percentage increase in people supplied. The two-level modelling technique showed no evidence of clustering of campylobacteriosis in any particular county. Aggregation of data on municipality level makes interpretation of the results at the individual level difficult. CONCLUSION: The increase in incidence of Campylobacter infections in humans from 1995 to 2001 was statistically significant from 1998. Treated water was a protective factor against Campylobacter infections in humans with an IRR of 0.78 per percentage increase in people supplied. Campylobacter infections did not appear to be clustered in any particular county in Norway.

Zoonoses in the Emergence of Human Viral Diseases.

Viral zoonoses have represented a significant public health problem throughout history, affecting all continents. Furthermore, many viral zoonoses have emerged or reemerged in recent years, highlighting the importance of such diseases. Emerging viral zoonoses encompass a vast number of different viruses and many different transmission modes. There are many factors influencing the epidemiology of the various zoonoses, such as ecological changes, changes in agriculture and food production, the movement of pathogens, including via travel and trade, human behavior and demographical factors, and microbial changes and adaptation. Cost-effective prevention and control of emerging viral zoonoses necessitates an interdisciplinary and holistic approach and international cooperation. Surveillance, laboratory capability, research, training and education, and last but not least, information and communication are key elements.

Reduction in flock prevalence of Campylobacter spp. in broilers in Norway after implementation of an action plan.

An action plan against thermophilic Campylobacter spp. in Norwegian broilers was implemented in May 2001. The action plan consists of three parts: a surveillance program including all Norwegian broiler flocks slaughtered before 50 days of age, a follow-up advisory service on farms delivering flocks positive for Campylobacter spp., and surveys of broiler meat products at the retail level. This article presents results covering the inclusive 3-year period between 2002 and 2004. During this period, a total of 10,803 flocks from 562 broiler farms were tested; altogether, 521 (4.8%) of the flocks were identified as positive for Campylobacter spp., primarily Campylobacter jejuni. The positive flocks originated from 257 (45.7%) of the farms. During the period 2002 to 2004, there was a large and steady reduction in flock prevalence, from 6.3% in 2002 to 3.3% in 2004. Also, the proportion of farms producing flocks positive for Campylobacter spp. each year reduced substantially, from 28.4% in 2002 to 17.8% in 2004. The proportion of flocks positive for Campylobacter spp. varied considerably with season and region. The action plan is a successful collaboration between academia, regulatory agencies, and the poultry industry that has resulted in a significant reduction in the number of broiler carcasses positive for Campylobacter spp. on the market. The temporal associations between implementation of the control program and the drop in the number of infected chickens and contaminated carcasses indicate that this collaborative action plan has been instrumental in achieving the goals of enhancing food safety.

What has happened in norway after the ban of avoparcin? Consumption of antimicrobials by poultry.

When avoparcin was prohibited for use as feed additive in poultry in Norway on 31 May 1995, an increased incidence of Clostridium perfringens-associated necrotic enteritis (NE) and an increase in the use of antibacterial (AB) drug therapy in meat-type poultry was expected. The consumption of AB drugs for use against NE in poultry in the period 1990-2001 was investigated by use of sales statistics at the drug-wholesaler level. Defined daily dose (DDD) per kg live weight poultry was the unit of measurement for drug use (to correct for differences in the dosages). Sales figures of the AB drugs were converted to number of DDDpoultry sold for the numbers of broilers at risk (broilers were 97% of the slaughter poultry). Estimated annual percentages of the broilers treated against NE increased abruptly after the avoparcin ban--but in 1996, this figure declined to the same level as before the ban and has remained at that low level since then. In November 1995, narasin was approved temporarily as an ionophore feed additive (IFA) in broilers. The usage patterns of IFAs in broilers were measured as the weight of feed to which an IFA was added per broiler chicken produced. In 1996-2001, the IFAs used in broilers were predominantly narasin. We note that the temporary increase in NE after the avoparcin ban coincide with the period before narasin became available. The increase in the consumption of AB drugs for the treatment of NE in poultry following the avoparcin ban has been negligible.

Prevalence of vancomycin resistant enterococci on poultry farms established after the ban of avoparcin.

Fecal samples from poultry on farms established after the ban of avoparcin (study farms) and from poultry on farms previously exposed to avoparcin (control farms) were examined for the presence of vancomycin-resistant enterococci (VRE). The samples were collected during the autumn and winter of 2001-2002. One isolate from each positive sample was selected, identified to species level, and examined for the presence of the vanA gene. The concentration of VRE and generic enterococci in the samples were also determined. In addition, the susceptibility to the ionophoric coccidiostat narasin was examined in a number of enterococcal isolates from poultry and in some enterococci of porcine origin that had not been exposed to narasin. VanA-type VRE was detected in samples from 64% of the study farms and 96% of the control farms. However, the concentration of VRE in the control samples was about six times larger than in the samples from the study farms. The minimum inhibitory concentration values for narasin differed between the poultry (1-4 mg/liter) and the porcine (0.25-0.5 mg/liter) isolates, indicating a decreased susceptibility towards narasin among enterococci from poultry.

Wildlife as source of zoonotic infections.

Zoonoses with a wildlife reservoir represent a major public health problem, affecting all continents. Hundreds of pathogens and many different transmission modes are involved, and many factors influence the epidemiology of the various zoonoses. The importance and recognition of wildlife as a reservoir of zoonoses are increasing. Cost-effective prevention and control of these zoonoses necessitate an interdisciplinary and holistic approach and international cooperation. Surveillance, laboratory capability, research, training and education, and communication are key elements.

Bacteriological analysis of fresh produce in Norway.

A total of 890 samples of fresh produce obtained from Norwegian markets were examined in order to assess the bacteriological quality of the products and their potential public health risk. The samples comprised lettuce, pre-cut salads, growing herbs, parsley and dill, mushrooms and strawberries. The samples were analysed for the presence of thermotolerant coliform bacteria (TCB), Escherichia coli O157, Salmonella spp., Listeria monocytogenes, Staphylococcus spp., and Yersinia enterocolitica. Neither Salmonella spp. nor E. coli O157 were isolated. For all product groups included, TCB were isolated from a small proportion of samples. Three samples harboured L. monocytogenes; one of the isolates belonging to serogroup 1 (champignons) and two of the isolates belonging to serogroup 4 (Chinese leaves and strawberries). Staphylococci were isolated from a relatively large proportion of the samples of strawberries and mushrooms. However, only four isolates were identified as S. aureus (non-toxinogenic). By the use of PCR, the presence of Y. enterocolitica was indicated in a few of the samples of lettuce, whilst no positive samples were found using a culturing method. The study shows that the occurrence of pathogenic bacteria and TCB in the products analysed was quite low. Nevertheless, the results indicate that the type of products analysed may contain pathogenic bacteria and thereby represent a risk to the consumers in regard to food-borne diseases.

Vancomycin-resistant Enterococcus faecium (VREF) from Norwegian poultry cluster with VREF from poultry from the United Kingdom and The Netherlands in an amplified fragment length polymorphism genogroup.

The genetic relationship between 197 vancomycin-resistant Enterococcus faecium (VREF) isolates and 21 vancomycin-susceptible E. faecium isolates from Norwegian poultry was analyzed by amplified fragment length polymorphism (AFLP). The isolates were compared to 255 VREF isolates from various sources and countries. The Norwegian isolates constituted a relatively homogeneous population of E. faecium and clustered in a previously defined poultry AFLP genogroup.

Genetic linkage between erm(B) and vanA in Enterococcus hirae of poultry origin.

Vancomycin-resistant enterococci (VRE) have frequently been isolated from Norwegian poultry production following the prohibition of the glycopeptide growth promoter avoparcin since 1995. In the present study, a close genetic linkage between the vanA and erm(B) determinants in an Enterococcus hirae isolate of poultry origin is demonstrated, a result that indicates a mechanism for co-selection and maintenance of vancomycin resistance in absence of selective pressure from avoparcin. A total of 36 vanA-positive enterococci of poultry origin, also phenotypically resistant to erythromycin and/or tetracycline, were analyzed by PCR for identification of erm and tet resistance determinants. An E. hirae isolate harbored erm(B) and tet(K), and in this isolate vanA and erm(B) were located on a BamHI fragment of an approximately 50-kb plasmid. Approximately 3 kb of this fragment was amplified by PCR with vanA and erm(B) primers. Sequence analysis of the region between erm(B) and vanZ of Tn1546 showed a truncated IS1216V inserted downstream of the erm(B) stop codon, aligned with a conserved copy of the 3'-inverted terminal repeat of Tn1546. Mating experiments with the E. hirae isolate as donor and E. faecalis JH2-2 as recipient did not result in any transconjugants, indicating that the vanA/erm(B)-carrying plasmid was nonconjugative under the given experimental conditions.

Within-sample and between-sample variation of antimicrobial resistance in fecal Escherichia coli isolates from pigs.

The present study was initiated to evaluate the effect of sampling time and within-sample variability on the diversity in antimicrobial resistance patterns in fecal Escherichia coli from healthy pigs. Isolates were tested against 11 antimicrobials. A total of 25 different profiles were observed, involving resistance to ampicillin, streptomycin, tetracycline, sulfonamides, trimethoprim, and/or a trimethoprim/sulfonamide combination. No isolates were resistant to enrofloxacin, gentamicin, or chloramfenicol, whereas resistance against neomycin and nalidixic acid was sporadically detected in isolates from grower pigs. A model that clusters pigs within-sampling time as a repeated factor and clusters isolates within individual pigs as a random factor was used. For sows, the variance component ratio of sampling time to residuals was 0.28-0.56 for the different antimicrobials (except ampicillin) and 0.85-1.79 for grower pigs. The variance components for within-sample variation were zero or close to zero, except in isolates from sows where resistance to ampicillin explained 14.8 times more of the variation compared to residuals. Thus, the effect of an animal's status at a given sampling time was more influential on the variability in antimicrobial resistance than within-animal diversity. We conclude that repeated sampling and analysis of one isolate per animal each time may be preferable for screening general tendencies, whereas several isolates have to be tested when individual animals are focused.